Intermittent Fasting in Trained Women Adds Same Amount of Muscle, Strips Extra Body Fat (4-6%) | No Effect of HMB

HMB did matter, but not significantly; and fasted training was not involved in the extra-fat loss and improvement in body composition.

While it has long been discussed if serious gainz are even possible on time-restricted feeding regimen, such as classic 'intermittent fasting', SuppVersity readers have known for years that "New 'Lean Gains' Study Confirms: IF Gets Athletes Lean & Improves Insulin Sensitivity W/Out Impairing Their Gains" (➡article discussing Moro 2016) - that's in men, though, and that, in turn, is one of several factors that make the latest study by Tinsley et al. (2019) worth looking at.

In their latest study, the Texas Tech University researchers combined two research questions into one study: (a) Does time-restricted feeding affect the adaptive response to resistance training women? (b) Can this effect be augmented and/or modulated by supplementing the leucine-metabolite HMB during the fasting phases (and once in the PM)?

Learn more about fasting at the SuppVersity

Monthly 5-Day Fast Works

"Lean Gains" Fast Works

Habits Determine Effects of Fasting

Protein Modified Fast 4 Health

IF + Resistance Training = WIN

ADF Beats Ca-lorie Restriction

You're wondering why on earth someone would still do research on HMB? Well, the study was supported by MTI Biotech Inc. who sell HMB and there's nothing reprehensible about financial support from the supplement industry... as long as it does not lead to irreproducible (and, for many, hardly credible) results as it may have been the case of the notorious free-form HMB study by Wilson et al. The reason we should still keep the role of the sponsor of which the scientists write that neither this nor the other supporter, Dyamatize, "play[ed] a role in the overall design or execution of the study, the analysis, and interpretation of the data, or the presentation of the results found in this article" is that sponsorship can lead to an often unconscious reporting bias and/or a certain emphasis on pro-supplement conclusions in the discussion of the results.

But we will get to potential issues with the presentation and interpretation of the results later. Let's first take a look at the study design as it is described in the abstract:

"This study employed a randomized, placebo-controlled, reduced factorial design and was double-blind with respect to supplementation in TRF groups. Resistance-trained females were randomly assigned to a control diet (CD), TRF, or TRF plus 3 g/d HMB (TRFHMB).

Figure 1: Study timeline and assessments. RT, resistance training (Tinsley 2019).

TRF groups consumed all calories between 1200 h and 2000 h, whereas the CD group ate regularly from breakfast until the end of the day. All groups completed 8 wk of supervised RT and consumed supplemental whey protein. Body composition, muscular performance, dietary intake, physical activity, and physiological variables were assessed. Data were analyzed prior to unblinding using mixed models and both intention-to-treat (ITT) and per protocol (PP) frameworks" (Tinsley 2019).

A closer look at what exactly the 18 and 30 y-old women with significant training experience (≥1 y of RT at a frequency of 2 to 4 sessions per week w/ weekly training of major upper- and lower-body muscle groups), who were recruited via posters, e-mail announcements, and word of mouth, did in this prospectively registered (clinicaltrials.gov) experiment.

Starting to Have Breakfast is Worst New Year's Resolution ... Unless You Want to Gain Weight more

Habituation effects were addressed: From my article about the habituation effect of breakfast eating on the metabolic effects of breakfast skipping and the ill effects of changing this habit, you will remember that it can be an issue if you put subjects who are used/not used to eating first thing in the morning on a time-restricted feeding regimen. Against that background it's of particular importance that Tinsley et al. (2019) stratified participant based on not just on BF% at screening (15–21% or >21%) but also based on their habitual breakfast consumption (≥5 d/wk compared with <5 d/wk), before they then randomly assigned the women to one of the three study groups using sequences produced from a random sequence generator.

Also noteworthy: The way fasting and training were timed precludes interference effects of fasted training... I mean, not that we could assume that this would explain the extra fat loss, anyway.

Here's the gist as far as diet, supplementation, and, obviously, the ladies' training regimen are concerned:

• ⏲ the feeding window of the TRF and TRFHMB participants was set to 1200 h - 2000 h each day, while and CD participants were instructed to consume breakfast as soon as possible after waking and to continue to eat at self-selected intervals throughout the remainder of the day;
• 🍕 the only dietary advice the subjects received was to hit their protein intake goals of by consuming whey protein supplement (regular concentrate, nothing fancy 💲 "Elite 100% Whey", Dymatize Enterprises, LLC) on both training and non-training days in order to achieve a protein intake ≥1.4 g/kg/d; 
• 🍣 the target energy intake was prescribed by multiplying resting energy expenditure (REE), assessed via indirect calorimetry, by an activity factor of 1.5 and then subtracting 250 kcal; in that, "[t]he goal of the small caloric reduction was to promote fat loss while still providing adequate nutritional support for muscular hypertrophy"; effectively, the women thus ate more, though that pre-intervention 250, 162, and 90kcal/day for CD, TRF, and TRFHMB, respectively;
• 🍱 the macronutrients averaged out at 28/40/32 for proteins, carbs, and fats - with no inter-group differences and a de-facto protein intake of 1.6g/kg per day in all three groups
• 💊 on top of the whey all subjects consumed, they received either placebo (calcium lactate) or calcium 3x1g HMB supplements; both were identical in appearance and taste, and were matched for calcium (102 mg), phosphorus (26 mg), and potassium (49 mg) content;

• 

  Table 1: Overview of the ladies' workout regimen. Workouts were supervised and took place in the PM (12-18h, with fasting subjects consuming their first meal early if they came in between 12-13h); 25g whey were consumed right after every workout (Tinsley 2019).

  💊x⏲ participants were instructed to ingest 2 capsules on 3 occasions each day: upon waking, midmorning while still fasting, and prior to bed, for a total dose of 3 g/d;
• 💊 the women "were discouraged from consuming any additional sports supplements beyond those provided by study investigators, with the exception of common multivitamin/mineral supplements" (Tinsley 2019).
• 💪 the ladies trained for 8-weeks under supervision and on three non-consecutive days each week (i.e., Mondays, Wednesdays, and Fridays), and 2 different upper- and lower-body sessions were alternated (Table 1); the women trained to momentary failure
• 🍽 the training times were not set in stone, but nobody was allowed to train fasted; hence participants who came in early in the training window from 12-18h, had to break their fast early

In short: The researchers mimicked what a dedicated but not necessarily crazy gymrat could, in fact, be doing for 8 weeks or even longer to improve her physique. Speaking of which, as the scientists report as early as in the abstract, all subjects saw...

Figure 2: Body composition data (per protocol analysis | in the intention to treat analysis, which includes all subjects regardless of adherence, the fat loss advantage was visible but not sign.)

• comparable fat-free mass (FFM) accretion 💪 (+2% to 3% relative to baseline) and skeletal muscle hypertrophy 🤹‍♀️ occurred in all groups, but ...
• statistically different effects on fat mass 🤟 (CD: +2%; TRF: −2% to −4%; TRFHMB: −4% to −7%) were observed in the per-protocol analysis (meaning, when only those who actually adhered to their protocol were included - for all subjects, including those who didn't fast appropriately the effect was no longer significant).

Finally, it's worth mentioning that "[m]uscular performance improved without differences between groups"; and that "[n]o changes in physiological variables occurred in any group, and minimal side effects were reported" (Tinsley 2019).

This study and the latest meta-analysis show: athletes & experienced gymrats don't benefit from HMB supplements.

Did you notice something? Yes, HMB is even mentioned... at least not until the scientists conclude the abstract to their study by somewhat cumbersomely referring to the fact that

"[s]upplemental HMB during fasting periods of TRF did not definitively improve outcomes" (that's my emphasis in a quote from Tinsley 2019).

To me, this seems to be even a tad bit too unbiased; because, as non-significant as the difference may be, the increased fat loss with HMB the scientists observed (cf. Fig.1 FM dark vs. light grey bars) is a recurring theme in HMB research... one of which the previously discussed HMB ↔ body comp. meta-analysis shows that it is yet by no means observed in every study (see Figure 2 | here).

Hence, the take-home is: breakfast skipping works for both sexes and the combination of a small caloric deficit with plenty of high-quality protein will improve your body composition.

So simply stating that "non-significant benefits" have been observed, in the conclusion to the abstract would be perfectly ok, IMHO. The strange "not definitively", on the other hand, could also imply that there some women would indeed benefit and will rather confuse than enlighten the reader without full-text access, whose take away message should be: in the short run and at moderate deficits of only -250kcal/d, time-restricted feeding in the form of breakfast skipping helps women lose extra body fat without measurable effects on lean mass acquisition (let alone loss) when protein intakes are high and high EAA proteins (whey) are provided | Comment!

References:

• Moro, Tatiana, et al. "Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males." Journal of Translational Medicine 14.1 (2016): 290.
• Tinsley, Grant M., et al. "Time-restricted feeding plus resistance training in active females: a randomized trial." The American Journal of Clinical Nutrition (2019).

Stevia: What's New in 2019? Appetite, Food Intake, Fertility, Metabolism, Microbiome | Plus: Is Your Stevia 'Natural'?

Stevia is available in all forms and combinations... often you don't realize before you take a look at the label that it was literally diluted with fillers and other sweeteners such as erythritol etc. Moreover, no one can reliably tell you if the exclusion of the "bitter stuff" and reliance on Rebaudioside A, exclusively, doesn't nullify some of the previously described health benefits of the whole plant.

I was just about to simply add the results of a recent study to your daily dose of research news on "FB/SuppVersity", when it occurred to me that it has been suspiciously quiet on the sweetener front, lately - specifically when it comes to stevia, a sweetener of which many people claim that it was "natural"... But is that true, is what you can buy at the supermarket or online really still "natural"?

While the former is certainly a question of your definition of natural" (do you think a highly processed, isolated white powder is "natural"?).

You can learn more about sweeteners at the SuppVersity

Aspartame & Your Microbiome - Not a Problem?

Sucralose 2018 Update #1 - Does it Make Us Fat?

Diet Soda Beats Water as Dieting Aid in RCT

Experiments Don't Support AS<>Obesity link

The Case Against Saccharin: Why it may be different.

Other Diet Soda Additives May be the Real Problem

There's one issue with the (often) Rebaudioside A based products from the shelves, no one can seriously question: Whether the results of studies that are done with the real thing, i.e. stevia leaves of which you could rightfully claim that they are "natural" sweetening agents, will almost certainly not translate 1:1 to the effects of consuming 'stevia' from commercial foods and beverages.

• So why is your "stevia" not the real deal? In view of the results of a recent study in the "Journal of Pharmaceutical and Biomedical Analysis" whose authors (Pacifico 2019) report fifty bioactive constituents in stevia leaves (UHPLC-ESI-QqTOF-MS/MS analysis), you cannot seriously expect that the white powder you call "stevia", which usually is water-extracted and chemical processed Rebaudioside A, the steviol with the least bitterness of all, plus all sorts of fillers and anti-caking agents, will have the same physiological effects on your body as this complex mix of phytochemicals.
  
  

  

  If you want to put that #chlorogenic acid that was lost when your "stevia" was produced back in, study my Coffee 101 it has all the details on how to maximize the CGA content of your home-brewed coffee.

  Speaking of compounds, among the fifty the study identified, non-phenol metabolites, such as benzyl primeveroside and roseoside, as well as a lignan polyphenol (5′), were reported for the first time as constituents of the Stevia leaf. Others, such as chlorogenic acid (the good stuff from coffee) have been detected before but few people are aware of their presence in the true natural sweetener, i.e. the stevia leaves.
  Practically speaking, this means: Your "stevia powder" must not boast any of the health-benefits studies ascribe to either stevia leaves or what scientists would call a 'crude extract'.
  
  This "real deal" forms of stevia have been found to blunt the digestion of carbohydrates, have potent anti-oxidant qualities, and can thus even help alleviate diabetes. With other recent studies showing that the whole leaves (including the bitter compounds) seem to prevent liver disease by modulating hepatic inflammation and fibrosis (Ramos‐Tovar 2018 & 2019), fibrosis and )

Ok, now that you've learned the news that you should have known all along: To call the white stuff from the supermarket a 'natural' sweetener is certainly questionable and unquestionably irrelevant...

Latest review confirms what you've read about sweeteners per se at the SuppVersity - Experimental evidence of ill effects = not convincing: If we widen the scope from Stevia to all non-nutritive sweeteners, it's worth  mentioning Ahmad et al. published in the July issue of "Current Opinion in Clinical Nutrition and Metabolic Care" (Ahmad 2019). The scientists pretty much agree with my previous assessment of the literature when they write that "[o]n the basis of the current evidence, we are still incapable of establishing a definite judgment on whether NNS use truly affects glycaemic control". The authors do however highlight the research on sucralose I analyzed in 2018.

...unless you're stupid enough to believe that everything that marketing people label "natural" is healthy. With that being said, you got to be careful not to (over)generalize the results of a recent review in Current Nutrition Reports which concludes:

"A growing body of evidence indicates that Stevia rebaudiana Bertoni is protective against malignant conversion by inhibition of DNA replication in human cancer cell growth in vitro. Consumption of Stevia has demonstrated to be generally safe in most reports. Further clinical studies are warranted to determine if regular consumption brings sustained benefits for human health" (Rojas 2018)

The same goes for another rave review from last year, in which Samuel et al. praise the promising research on stevia's effects on metabolism, its safety, impact on blood glucose and insulin concentrations, energy intake and weight management, blood pressure, dental caries, naturality and processing, taste and sensory properties (Samuel 2018), and obviously the research results from the last 12 months I've promised in the intro of this article:

• Artificial and sweeteners, obesity, and (in-)fertility revisited - Stevia sticks out: negatively - even compared to aspartame! You may remember from the good old days of short daily SuppVersity articles that there is evidence (from rodent studies) that stevia may impair female fertility... well, a new study (Cho 2018) that investigated the interaction between obesity, low-calorie sweeteners, and prebiotic oligofructose on reproductive parameters - once again in rats, obviously - reports that...
  
  ... stevia, when delivered at 2-3 mg/kg/d in the drinking water, reduces the rate of successful pregnancies by another -7% over the effects of obesity, alone!
  
  In this context, it will come as a relief to overweight human mothers to be who are already pregnant that those 53 percent of the rats who became pregnant had 100% pregnancy and delivery indexes - in other words: the effect must occur before the fertilized egg nests and starts to divide. With only a handful of studies on potential fertility effects of stevia, we are yet far from being able to say with certainty that a high/regular consumption of the "natural" (and, hence, in way too many people's minds "healthy") sweetener poses absolutely no threat to female fertility ... especially if the latter is already endangered by obesity!
• Do sweeteners just make you hungry? No... and for stevia the opposite may be the case! The former is at least what a recent study from the University of Manchester seems to suggest (Stamataki 2019).
  
  For said study, the authors tested in a randomised controlled double-blind crossover trial, how the energy intake of healthy participants (n = 20, 9 males, mean body mass index 21.8 kg/m²) was affected by having different beverages 30 minutes before an ad-libitum (have as much as you want) lunch condition. The test beverages included (C) 330 mL of water (control-no calories and no taste) and either 330 mL of water containing (1) 40 g glucose or (2) sucrose (sweet taste and calories), (3) maltodextrin (calories and no sweet taste), or (4) 240 ppm all-natural sweetener, stevia (Truvia RA-95-sweet taste and no calories).
  
  The additional questionnaires revealed that the stevia and glucose preloads were rated to have equal sweetness levels, while water and maltodextrin the lowest levels of sweetness. As you would expect, though, "only glucose, sucrose and maltodextrin elevated blood glucose" (Stamatki 2019) - interestingly, both the almost non-sweet maltodextrin and the similarly sweet calorie-containing glucose and sucrose, and the stevia treatment significantly suppressed the participants' (all compared to water). What's more important, though is that these observations also translated to the objective (and actually relevant) study outcome: food intake on the ad-libitum meal:

  "Compared to water preload, food intake was significantly lower after the consumption of each of the sweet or caloric preloads" (Stamatki 2019).

  What about stevia? Well, the conclusion of the study says that the study "found a beneficial effect of a stevia beverage consumed prior to a meal on appetite and subsequent energy intake" (Stamatki 2019) - so where's this benefit?
  
  

  

  Figure 1: The figure depicts the cumulative energy intake for all five intervention groups (Stamatki 2019)

  It appears only in the analysis of the subjects cumulative energy intake (preload and lunch), which showed that total energy intake was lower after the stevia preload compared to the water preload.
  
  The latter, i.e. a significant effect compared to water must yet not make us forget that this advantage did not persist when compared to the caloric preloads, which made up for the extra-calories they delivered by suppressing food intake more significantly.
  
  Needless to say, that 24h follow-ups, habituation effects, and - most importantly - studies in people whose natural ability to self-regulate their body weight seems to be impaired - are warranted before advising people to consume a stevia-sweetened beverage before a meal to reduce their overall energy intake... 'cause, after all, we all know that that is what really counts.
• Like everything you eat, stevia will affect your microbiome - the question is: For good or for bad? Further insights into stevia's effects on the microbiome come from University of Calgary (Nettleton 2019), where researchers conducted a rodent study the results of which are worth reporting despite the somewhat uncertain transferability to human beings.
  
  You've read about a putatively negative effect of stevia and "un-"natural sweeteners on the SuppVersity before. You are also well-informed about the under-researched and overhyped role of the gut microbiota as an "important environmental factor that can mediate metabolism and subsequent obesity and disease risk" (Nettleton 2019). To further our insights into what is a much more complex relationship than the NY Times article you may have read (and trusted) suggests, Nettleton et al. didn't just want to confirm and further analyze the stevia-mediated changes in gut microbiota, they also wanted to know if they could be prevented or reserved by the provision of pre-biotics, i.e. food for the allegedly good bacteria. To this ends, they conducted the following experiment:

  "Three-week old male Sprague-Dawley rats were randomized to consume: (1) Water (CTR); (2) Rebaudioside A (STV); (3) prebiotic (PRE); (4) Rebaudioside A + prebiotic (SP) (n = 8/group) for 9 weeks. Rebaudioside was added to drinking water and prebiotic oligofructose-enriched inulin added to control diet (10%). Body weight and feces were collected weekly and food and fluid intake biweekly. Oral glucose and insulin tolerance tests, gut permeability tests, dual X-ray absorptiometry, and tissue harvest were performed at age 12 weeks" (Nettleton 2019).

  With 2-3mg/kg Rebaudioside A, the rodents were fed the human equivalent of approximately 14-15mg which is way below the ADI set by the Health Canada (which is  4 mg/kg bw/day for adults). It is thus not 100% surprising that the study did not reproduce the weight loss effects some previous studies using 30-50-fold higher dosages observed. In a similar vein, the rodents glucose tolerance seemed to be pretty stable - and that's despite the fact that ...

  "[...] the administration of Rebaudioside A did, however, alter gut microbiota composition and reduce nucleus accumbens tyrosine hydroxylase and dopamine transporter mRNA levels compared to CTR" (Nettleton 2019).

  Now, while this may sound pretty bad, it's where the actual news comes in, as the scientists found that the ill effects on the microbiome was attenuated by the provision of prebiotics in the rodents' diet. Moreover, both the prebiotic, alone, as well as the prebiotic + Rebaudioside A group, had reduced fat mass, food intake, gut permeability and cecal SCFA concentration - all four well-known 'side effects' of probiotics.

While the changes in dopamine availability may suggest that the provision of stevia increases the risk of overeating, the rodents intake of the (albeit blatant) diet was unaffected (top); much in contrast to the composition of the microbiome (bottom).

Whut? Stevia reduces dopamine? This is exactly what the Nettleton study shows. If you scrutinize what the scientists analyzed, though, you will realize that their data relates exclusively to the dopamine production and uptake in the mesolimbic reward circuit, where RebA reduced tyrosine hydroxylase (TH | p = 0.044) and dopamine transporter (DAT | p = 0.044) mRNA levels in the nucleus accumbens. In previous studies, similar changes have been linked to food overconsumption - an effect that was, as the figure on the left goes to show you, yet not observed in the study at hand. In view of the fact that the rodents were fed a rather blatant diet the lack of dopamine (~reward) has been linked specifically to the overconsumption of highly palatable food, in particular, any form of definite all-clear signal seems to be unwarranted - especially in view of the fact that these (anti-)dopaminergic effects may well be a downstream effect of the "natural" sweetener on the microbiome (that would also explain its attenuation by prebiotics in the ventral tegmental area,  a group of neurons located close to the midline on the floor of the midbrain).

• What the study adds, though, is that these benefits were not abolished by the coadministration of Rebaudioside A ... well, ok, if you like to poop, you may complain that 'stevia' triggered a significant reduction in cecal weight.
  
  

  

  SIBO-sufferers beware of pre- and probiotics. While they may counter some of the potentially 'bad' effects of stevia, they may mess you up big time | more.

  If you're a stevia junkie it would thus seem prudent to make sure that you get your daily dose of probiotic fiber in your diet ... but wait: if you're already suffering from dysbiosis and or SIBO the 10% FODMAP diet (oligofructose-enriched inulin), the rodents in the study at hand received may actually do more harm than good - as an avid SuppVersity reader you knew that all along, though, right (learn more about SIBO and pro/prebiotics)? If you experience abdominal pain, bloating or the previously discussed brain fog in response to adding inulin rich foods to your diet, you're thus better off with stevia alone.

Suggested read from the SuppVersity Archives: "Can Stevia Help You Ward Off Type II Diabetes? A Review" | Read the full article and/or all posts tagged with stevia from the archives

Stevia, the microbiome and... your teeth! While I suppose that the previous elaborations already gave you more than enough input to think about, there's still one study from early 2019 I would like to mention as it (re-)emphasizes something we tend to overlook over all the hype about the intestinal microbiome: our digestive tract starts in our mouths. In fact, the mouth was the first place where we realized the (in-)direct effects of certain bacteria on our health - the effects of bacteria in the plaque on our teeth on our oral hygiene, the structure of our teeth and, as more recent studies suggest (Noble 2013; Tonsekar 2017; Maldonado 2018), downstream effects of ill oral hygiene and rotten teeth on our dementia (including Alzheimer's) risk.

Said study by Siraj et al. (2019) reports that rinsing for 1 minute with 0.2% aqueous solution of Stevia leaf extract at night reduces the number of acid-producing bacteria on the subjects' teeth to an extent that abolishes the pH decrease in response to the consumption of their favorite food: sugar. What is interesting here is that similar effects were observed for the full-spectrum stevia extract and a commercially available stevioside-based sweetener the scientists used as a comparison in their study ... Why's that interesting? Because it suggests that major microbial effects of stevia remain intact when the sweet compounds are isolated, packaged with fillers and sold as a sugar-alternative, exactly those products of which I initially warned you that they are not identical to the actually "natural" sweetener stevia rebaudiana | Comment!

References

• Ahmad, Samar Y., et al. "Recent evidence for the effects of nonnutritive sweeteners on glycaemic control." Current Opinion in Clinical Nutrition & Metabolic Care 22.4 (2019): 278-283.
• Cho, Nicole A., et al. "Impact of Food Ingredients (Aspartame, Stevia, Prebiotic Oligofructose) on Fertility and Reproductive Outcomes in Obese Rats." Obesity 26.11 (2018): 1692-1695.
• Nettleton, Jodi E., et al. "Low-Dose Stevia (Rebaudioside A) Consumption Perturbs Gut Microbiota and the Mesolimbic Dopamine Reward System." Nutrients 11.6 (2019): 1248.
• Noble, James M., Nikolaos Scarmeas, and Panos N. Papapanou. "Poor oral health as a chronic, potentially modifiable dementia risk factor: review of the literature." Current neurology and neuroscience reports 13.10 (2013): 384.
• Pacifico, Severina, et al. "New insights into phenol and polyphenol composition of Stevia rebaudiana leaves." Journal of pharmaceutical and biomedical analysis 163 (2019): 45-57.
• Ramos‐Tovar, Erika, et al. "Stevia rebaudiana tea prevents experimental cirrhosis via regulation of NF‐κB, Nrf2, transforming growth factor beta, Smad7, and hepatic stellate cell activation." Phytotherapy Research 32.12 (2018): 2568-2576.
• Ramos‐Tovar, Erika, et al. "Stevia prevents experimental cirrhosis by reducing hepatic myofibroblasts and modulating molecular profibrotic pathways." Hepatology Research 49.2 (2019): 212-223.
• Rojas, Edward, et al. "Stevia rebaudiana Bertoni and its effects in human disease: emphasizing its role in inflammation, atherosclerosis and metabolic syndrome." Current nutrition reports 7.3 (2018): 161-170. 
• Samuel, Priscilla, et al. "Stevia leaf to Stevia sweetener: Exploring its science, benefits, and future potential." The Journal of nutrition 148.7 (2018): 1186S-1205S.
• Siraj, E. Saira, K. Pushpanjali, and B. S. Manoranjitha. "Efficacy of Stevioside sweetener on pH of plaque among young adults." Dental research journal 16.2 (2019): 104.
• Stamataki, Nikoleta, et al. "Beneficial Effects of Consuming a Natural Zero Calorie Sweetener Preload Prior to Lunch on Energy Intake: A Double-blind Randomised Crossover Study (FS18-01-19)." (2019): nzz041-FS18.
• Tonsekar, Pallavi P., Shuying S. Jiang, and Gang Yue. "Periodontal disease, tooth loss and dementia: is there a link? A systematic review." Gerodontology 34.2 (2017): 151-163.

10%(+) Reduction in Testosterone After Glucose and Whey Protein Shakes - Is the Classic #BB Shake Anti-Anabolic?

We're talking about a cross-over study in adolescent subjects and acute changes but that's neither the only nor the most relevant reason you don't have to be afraid of the bodybuilding staple, now. In fact, a closer look at the data seems to suggest that we're talking about a 'protein-anabolic decrease in testosterone'... sounds odd? Well, here's how it may relate to your #androgenReceptors (AR) and eventually your gainz, irrespective of your age, by the way.

I have previously addressed the possible ill effects of very high protein intakes on your testosterone levels - in particular, when those intakes are combined with a caloric deficit and, accordingly, reduced intakes of glucose and fat (re-read "True or False - High or Low Protein Intakes Have Profound Influence on Testosterone, SHBG, Estrogen, Cortisol & Co?" | here)... Now, a new study in Clinical Endocrinology (Schwartz 2019) shows that testosterone ⇆ protein/carbohydrate interactions trigger significant acute decreases in serum testosterone levels in those whose testosterone levels should be soaring: adolescent males.

Read more about studies involving TRT/HRT & co on suppversity.com:

What to expect from normalizing Testosterone

Testosterone Gel Augments 'ur Gainz

PWO T-Increases Don't Determine Your Gainz

The Hormonal + Other Underpin-nings of Gainz

Impressive 12% T-Boost (+20% IGF1) W/ Tribulus

T +/- Exercise to Rejuvenate Old Muscle?!

Needless to say that this raises the question: Does that mean that a classic #bodybuilding staple, the high carb, high protein post-workout shake, will ruin your 'muscle building hormone' (learn more)?

The study Schwartz et al. conducted in twenty‐three adolescent males (12‐18 years old; only those with testosterone levels indicating mid-late puberty were included in the analysis) measured the levels testosterone, as well as luteinizing hormone (LH), GLP‐1 (active), ghrelin (acylated), glucose, insulin and subjective appetite prior (0) and at 20, 35 and 65 minutes after the consumption of a test-beverage; a test beverage that contained...

"...either 1 g of glucose monohydrate (BioShop Canada Inc, Burlington, Ontario, Canada) or 1 g of protein (plain whey protein isolate; BiPro USA) per kg of body weight [...] A noncalorie drink was used as control" (Schwartz 2019).

With a protein content of 90.4% (5.7% moisture, 2.2% ash, 1.18% fat and 0.6% carbohydrates), these test beverages were eventually only 'almost' isocaloric, though: 3.74 kcal/kg body weight for the protein and 4 kcal/kg body weight for the sugar shake is yet not far enough apart to invalidate the study results and the flavor was standardized:

"All beverages were flavoured with 1.5 mL of chocolate extract (Vanilla Food Company) to account for the flavour differences and mixed with 500 mL of water, similar to previous protocols.The whey protein and control beverages were sweetened with 0.2 g sucralose (Tate & Lyle) in order to match sweetness with the glucose beverage. Sucralose was chosen as it has been shown to have no effect on postprandial plasma glucose or insulin. Test beverages were prepared the evening before the study and refrigerated in order to be served chilled the following morning. Participants were served the drink in a large covered opaque cup through a straw" (Schwartz 2019).

In the 3xAM sessions that took place, each after a 12h fast, all participants of this cross over trial had to consume the randomly selected beverages (protein, glucose, control) within 5 minutes. In order to wash away any potential aftertaste, they topped that off with 50 mL of plain water.

Testosterone level changes from baseline to 60 min after ingesting the glucose/protein beverage in pre-early puberty (n = 8) and mid-late puberty (n = 13) | results of a previous study by Schwartz (2015).

Where does the idea of reduced T in adolescents even come from, anyway? Schwartz et al. actually did the study under review as a follow-up to their 2015 study in which they observed an acute decrease in serum testosterone after the consumption of a mixed glucose and protein beverage in order to identify whether glucose and protein, each on its own would have similar or the same ill effects on male adolescents postprandial testosterone levels as the researchers observed them in 2015. Reductions as high as -20% in male adolescents in the mid-late phase of puberty (see Figure on the left).

Since the scientists also speculated that these liquid snacks would have different effects on the subjects appetite and, more importantly, ad-libitum food intake, the boys/young men were fed an ad libitum pizza meal after the final blood draw. In that, the "[p]articipants were instructed to eat [pizza] during the next 20 minutes until comfortably full. Based on prescreening participant preferences" (Schwartz 2019 | Pepperoni pizza (87 g) contained 9 g protein, 6 g fat and 23 g carbohydrates for a total energy content of 180 kcal); three‐cheese pizza (81 g) contained 10 g protein, 6 g fat and 23 g carbohydrate for a total energy content of 180 kcal).

Significant differences in terms of the number of slices of pepperoni and/or three-cheese pizza were not observed. Neither in form of treatment nor baseline body weight. 

In other words, with ~1,300 kcal the pizza love (or rather food intake) of the boys was not influenced by either the beverage or the boys' weight status (F = 2.23, P = 0.14). That's in contrast to the testosterone levels which differed significantly when the scientists compared the testosterone response of overweight and normal-weight adolescents (Figure 1.B).

Figure 1: Differential effects of treatments by weight status (A), overall effect of weight status on plasma testosterone (B).

In that, Figure 1.B seems to suggest that lean individuals (mean BMI = 21.1 ± 0.9 kg/m²) are more susceptible to the detrimental effects of protein/carbohydrate shakes than overweight/obese ones (mean BMI = 29.8 ± 1.2 kg/m²). In fact, though, the differential effects of treatments by weight status that are plotted in Figure 1.A, as well as the lack of an asterisk below the open "normal weight" bar in Figure 1.B tell you that the ostensibly large changes in testosterone the scientists observed in the 12 normal-weight subjects were overall non-significant.

So, being overweight or obese seems in fact to modulate the effects of glucose and protein beverages on adolescents' ... as it is common for every extra pound you carry, negatively.

Table 1:  Baseline levels of appetite‐ and sex‐related hormones (Schwartz 2019); interestingly enough, the level of these metabolically relevant measures didn't change differently for normal- vs. overweight subjects in response to either PRO or GLU.

Does that mean that being fat sucks? Well, let's check if any of the metabolic parameters can explain the difference: At least based on the changes that were reported in the FT, that was not the case - while insulin, GLP1, and ghrelin increased, increased and decreased in response to the beverages, they did so to a similar extent in all adolescents. More importantly, though, ...

...there were no differences in the insulin, GLP1 and/or ghrelin response when comparing the protein vs. glucose beverages.

In the absence of treatment effects on the satiety and hunger hormones, it is no longer that surprising that the scientists didn't observe measurable (and significant) effects on the subjects' pizza intake (reported further towards the beginning of this article) - and that despite the fact that all participants' subjective appetite was decreased after the glucose (no, not the protein) beverage (p = 0.0198 for control and p = 0.0247 for protein).

So what's the main takeaway message, then? Is it "Boys love pizza, no matter what?" 

Well, that could be one takeaway, but I think that Schwartz et al. are right to point towards three other results when it comes to the takeaway messages:

• both, glucose and protein shakes acutely lower the testosterone levels of adolescent males, 
• but the effect is not mediated by the macronutrient composition of the liquid meals, 

Moreover, the levels of testosterone the scientists measured in their young subjects' blood or, rather, the changes that were induced by the protein and glucose beverages did not correlate with the regulation of appetite or food intake. The latter was, however, what the scientists had expected when they planned this follow-up to their previously mentioned 2015 study.

This is not an outlier study and similar effects can be expected in older men: The study at hand has by no means produced revolutionary new evidence. In fact, it rather adds to the results of previous research and the testosterone decline(s) that were observed in Caronia et al. 2013 in men who consumed 75g of glucose and Schwartz' previously referenced study in overweight/obese adolescents from 2015, for example (see previous infobox).

The underlying mechanisms of these effects, however, are still not clear. As the scientists from the University of Toronto point out, the changes may be initiated ....

Table 2: Relationships between testosterone and luteinizing hormone with dependent measures (Δ from baseline means).

"by the intake of glucose or amino acids, particularly leucine, which stimulates rapamycin (mTOR) signalling and subsequent protein synthesis" and/or their "inhibitory effect on adenosine monophosphate‐activated protein kinase (AMPK)," (Schwartz 2019)... 

which should - theoretically - have increased the androgen receptor (AR) mRNA expression (Shen et al. 2014 observed the opposite effect, i.e. AMPK up = AR down in prostate cancer cells and it's likely similar effects will occur in skeletal muscle).

Your androgen receptor status may not just determine how much muscle you gain - the data from Morton et al. seems to suggest that it even determines if you make visible muscle gains, at all (learn more in my August 2018 article with the title "If the Androgen Receptor Response to Training Determines Your Gainz, the Question is: How Can You Optimize 'ur AR Density? Training-, Diet-, and Supplement-Effects Reviewed".

So, does it all come back to androgen receptors? Unlike acute changes in testosterone, the androgen receptor density on your muscles has recently been shown to significantly affect the gains of resistance trained men. I discussed the corresponding study at length in a SuppVersity article from August 2018. What I may or may not have highlighted enough in that context is that...

...any increase in androgen receptor (AR) expression leads to greater testosterone uptake by the muscle tissue which lowers plasma testosterone levels... and that probably to an extent similar to what was observed in the study at hand!

This may also explain why neither glucose nor protein has ever been shown to have anti-anabolic effects. In fact, if their isolated and combined consumption in form of a beverage does indeed increase the AR receptor expression and lower the levels of circulating testosterone only by increasing the amount of T that's bound to receptors, that's even more evidence that, on the endocrine level, both nutrients exert pro- not anti-anabolic effects. Accordingly, the notion that the study at hand would support low-carb keto- vs. classic high protein + low-fat-diets for bodybuilders and anyone else striving for a muscular physique would be fundamentally flawed... but let's not jump to conclusions, here! It will be up to other, long(er)-term studies that include resistance training regimen and more relevant outcomes (=changes in body composition) to say which dietary pattern is best for your gainz - as of now, it seems to make less of a difference than people on either side of the nutritional divide want to make you believe - that is, assuming that the dietary protein and energy intake are equal in a low vs. high carb diet | Comment!

References:

• Caronia, Lisa M., et al. "Abrupt decrease in serum testosterone levels after an oral glucose load in men: implications for screening for hypogonadism." Clinical Endocrinology 78.2 (2013): 291-296.
• Schwartz, Alexander, et al. "Acute decrease in serum testosterone after a mixed glucose and protein beverage in obese peripubertal boys." Clinical Endocrinology 83.3 (2015): 332-338.
• Schwartz, Alexander, et al. "Acute decrease in plasma testosterone and appetite after either glucose or protein beverages in adolescent males." Clinical Endocrinology (2019).
• Shen, Min, et al. "The interplay of AMP‐activated protein kinase and androgen receptor in prostate cancer cells." Journal of cellular physiology 229.6 (2014): 688-695.

Will Adding 100mg of GABA to Your Whey Turn You into GH-ulk? RCT Finds 10x Higher Total Lean Mass Gainz, BUT...

Sometimes study results just seem too good to be true... I mean, who cares about total lean (including organ) mass when everything you can show off: strength, arms, and legs didn't grow appropriately? You don't? Well, the study is still interesting. Or did you anticipate that, in young-to-middle-aged training noobs GABA probably has to be cycled to keep its effects on growth hormone (GH)?

I've previously told you about #GABA, I also highlighted that it's questionable whether its use as a growth hormone (#GH) booster is actually going to yield visible improvements in your physique... on the other hand, the GH response to workouts was - next to cortisol - the only hormonal correlate West et al. (see Figure 1, in previous article) observed in the best and IMHO only decently well powered long(er)-term study investigating what Stuart Philips called "a hormonal ghost" (Philips 2012), i.e. the contribution of the transient increase in growth hormone, testosterone, IGF1, etc. in the hour/s after a workout.

Now, GABA has been found to trigger similarly transient increases in GH as resistance training. Unlike the effects of straight exogenous human growth hormone (#HGH), the effects of GABA on muscle protein synthesis have not yet been studied in humans... not yet? Yes, this means it has been done.

Learn more about building muscle and strength while losing fat with www.suppversity.com

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Pre-Exhaustion Exhausts Your Growth Potential

Exercise not Intensity Variation for Max. Gains

Battle the Rope to Get Both, Ripped and Strong

Study Indicates Cut the Volume Make the Gains!

In their latest paper, scientists from the R&D department of Pharma Foods International report on the results of an experiment in which they examined "the effects of oral GABA plus whey protein supplementation on muscular hypertrophy in men after progressive resistance training" (Sakashita 2019). In that, you guessed it, ...

 the not exactly 100% unbiased scientists hypothesized that "GABA administration with post-exercise protein supplementation may enhance training-induced muscle hypertrophy concomitant with elevated resting plasma GH concentrations" (ibid.)

To test the hypothesis, the scientists conducted a randomized double-blind parallel-group design study involving N=21 healthy, non-exercising men (26 - 48 years) who were randomized to receive

• whey protein isolate (Lactocrystal®) at a daily dosage of 10 g) or the same
• whey protein isolate  + 100 mg of GABA (80% pure Pharma GABA® produced by fermentation) 

daily for 12 weeks. With regard to the way the supplement was consumed, the scientists write:

"Subjects were instructed to ingest the supplements within 15 min of training, or before sleep on a non-exercise day. Each supplement was dissolved in 150 mL water immediately before ingestion." 

The whey protein powder was a whey protein isolate (Lactocrystal®; Nippon Shinyaku Co., Ltd, Kyoto, Japan); the GABA powder was produced through natural fermentation using a specific lactic acid bacteria strain (Pharma GABA®; 80% purity; Pharma Foods International Co., Ltd, Kyoto, Japan).

If you want to stack something w/ your whey protein, it should be creatine - especially if you're a vegan (elderly) trainee as you've learned in my 2017 article "Creatine Non-Responder? Age+Meat Intake - Determinants of Creatine's Effect on PCr (±200%) + Probably Performance".

How did they train? Here's the authors' summary: "The resistance training program included five upper-body and lower-body exercises: leg press, leg extension, leg curl, chest press, and pull down (LifeFitness, Schiller Park, IL, USA). Both groups performed the same training program. Training sessions were completed within 60 min and included the following: 5 min, warm-up (ergometer cycling); 45 min, resistance exercise; and 10 min, stretching exercise.

This training program was performed twice per week in a fitness club with training equipment and included one unsupervised and one professional trainer-supervised session per week. All resistance exercises were performed in three sets (12 repetitions; 2 - 3 min rest periods).

[...] Exercise intensity was set at 50% maximal strength for the first week and then raised to 60% after week 1. Weights were progressively increased in 2.5 - 5 kg intervals when the prescribed repetitions could be completed. The trainer ensured that subjects provided maximum effort and intensity for all supervised training sessions. Subjects were instructed to only perform exercises as part of the training program; those who missed three exercise sessions were excluded from the analysis" (ibid.) - whether the non-preregistered study was adequately powered was not reported, by the way ... 🤔

The main outcomes were the 12-week increases in maximal strength which were not tested directly, but calculated by dividing weight by percentage of RM, as well as body composition (fat-free mass, fat mass, and total body mass), which was assessed for all subjects using dual-energy X-ray (#DXA) absorptiometry, and plasma GH concentrations, which were measured using a commercially available enzyme-linked immunosorbent assay for human GH.

As it's common for any training + supplementation study, not all subjects made it to the finish line: Five subjects excluded from the analysis because of personal reasons (WP, n = 1; WP + GABA, n = 1), not completing 90% of supplement intake requirements (WP, n = 1), and not completing 90% of exercise sessions (WP, n = 1; WP + GABA, n = 1). Thus, 21 subjects completed the 12-week program (WP, n = 10, 40.1 ± 7.9 years; WP + GABA, n = 11, 38.8 ± 5.7 years). For all of them, it can be said that:

Neither the training nor the supplements significantly changed either the energy content or the macronutrient composition of the subjects' diets!

What the combination of resistance training + 10g of whey that was consumed on top of rather marginal protein intakes of 1g/kg body weight per day did, though, was to trigger significant changes in body composition - total lean mass to be precise.

Figure 1: Change in body composition after 12 weeks as measured using dual-energy X-ray absorptiometry. (a) Whole body fat-free mass and (b) arm and leg lean mass. Values represent the mean ± standard error for 10 subjects (WP) or 11 subjects (WP + GABA). *P < 0.05 vs. the WP group (Sakashita 2019).

Now, that's per se not surprising. After all, we're talking about training noobs, but what is surprising (at least to me) is both the statistical significance as well as the absolute size of the differences in lean mass gains in the "whey only" vs. "whey plus GABA" group, you can see in Figure 1.

Figure 2: Max. strength increased significantly in both groups, but there was absolutely no effect of GABA - not even on leg presses (p = 0.040), bros - and it happens to be in line with the observations in West 2012: no interaction between GH and strength (Sakashita 2019).

A significant time effect was also observed for the strength parameters which increased

Two additional observations are interesting and potentially worth considering: the difference between total extra lean mass gains and arm and leg lean mass gains (Figure 1), and the decline of the GH boosting effects of GABA over time (Figure 3).

In fact, if you scrutinize the data in Figure 3, you will realize that timing is the only relevant inter-group difference - the direct comparison of the increases didn't yield significant results (even if it may initially look like that).

You may have to cycle GABA to see benefits: Before we draw some final conclusions, though, let me briefly address what I consider to be an important but easily overlooked implication of the study at hand: if it even works, you probably need to cycle GABA, as its effects wear off within 1-2 months and it's not clear if they return after another 2 months of abstinence... since you'll by then be no newby, anymore, it's questionable whether this 2nd 'cycle' will yield significant results, at all - even in the less relevant "total lean mass" category. Ah, ... and with the age of the study's participants ranging from the early-20s to the mid-40s, the corresponding "GABA-cycling"-trial should also investigate whether the need for and/or optimal timing of these cycles depends on biological, not just on training age.

What? Ok, let's rephrase that: (a) both WP + GABA + training and WP only + training lead to statistically significant increases in growth hormone, but (b) it took 8 weeks vs. 4 weeks in the WP only group for these changes to reach statistical significance over the baseline levels in this group - and again (c) an inter-group difference was not observed at any point during the study due to the high variability of the GH levels.

Figure 3: Resting plasma growth hormone concentrations. Values represent the mean ± standard error for 10 subjects (WP) or 11 subjects (WP + GABA). *P < 0.05 vs. baseline of the WP + GABA group; **P < 0.05 vs. baseline of the WP group.

So what do we make of these results, then?  Well, let's first address the usual confounders: (a) the subjects were untrained, results may differ for a trained population (the amount of lean mass gained, for example, is likely to be smaller), (b) protein nutrition is beyond current recommendations for strength trainees (up to 3g/kg | ISSN), hence different overall gains and inter-group differences may be expected from studies in populations with higher protein intakes.

Weight lifting shoes don't make a difference and "elevation masks" (those things that simply impair your ability to breath) work... they increase your cerebral oxygenation - don't rely on the potentially misleading abstracts, alone... read SuppVersity - and this 2019 research update, in particular!

Now for the exciting question: Does this study show that daily GABA supplementation helps to enhance exercise-induced muscle hypertrophy? The answer is more straight forward than you'd expect: No, it doesn't!

The study demonstrates that there are beneficial effects in terms of total lean mass. Since the latter includes organ mass and the subjects' "organ-free" arms and legs didn't grow faster, the scientists are right to limit their conclusion to "daily GABA supplementation may help enhance exercise-induced muscle hypertrophy" (my emphasis in Sakashita 2019).

Disappointed? Well, the mere fact that the Japanese scientists observed a difference in hypertrophy-related outcomes in response to the co-supplementation with GABA, at all, is newsworthy, IMHO. We do yet have to avoid to be carried away by impressive relative increases of only semi-relevant study outcomes. After all, anything that goes beyond the conclusions that there's some interaction with total lean body mass (but not the typical hypertrophy targets of resistance training: arms and legs) going on would be a misinterpretation (see red Box on cycling) for another caveat). To go beyond these two fundamental statements is speculation...

... so let's speculate! 

As the authors highlight GABA could "enhance muscle hypertrophy [due] to its ability to increase basal GH concentrations"; and, at first, the data seems to support that... "at first", i.e. until you realize that significant inter-group differences in the GH levels between the WP and the WP + GABA group were not detected at any time-point of the study.

Accordingly, it makes sense look further to potential "gain mediators" that were not measured in the study at hand... which ones? Well, what about improvements in sleep quality and fatigue reduction as they have been previously reported by Yamatsu et al. (2016) three years ago? As the authors of the study at hand readily themselves admit, we'd have to do a second study to investigate potential effects on sleep, HRV, subjective stress, and training motivation, which could all be affected by GABA supplementation. Moreover, studies in trained individuals and with more appropriate protein intakes (>2g/d vs. ~1g/day) are warranted and the scientists should make sure that the 1kg increase in lean mass is not a consequence of increased glycogen storage (learn why), which could be a side effect of the interactions between GABA and glucose metabolism (Gomez 1999; Wan 2015) and or endocrine functions other than growth hormone (Erdö 1990; Gladkevich 2006; )... so, in essence: little do we know, but we are intrigued, right? Don't worry, I will keep you posted here and in the SuppVersity Facebook News at www.facebook.com/SuppVersity | Comment!

References:

• Erdö, Sándor L., and Joachim R. Wolff. "γ‐Aminobutyric acid outside the mammalian brain." Journal of neurochemistry 54.2 (1990): 363-372.
• Gladkevich, A., et al. "The peripheral GABAergic system as a target in endocrine disorders." Autonomic Neuroscience 124.1-2 (2006): 1-8.
• Gomez, Rosane, et al. "GABA agonists differentially modify blood glucose levels of diabetic rats." The Japanese Journal of Pharmacology 80.4 (1999): 327-331.
• Phillips, Stuart M. "Strength and hypertrophy with resistance training: chasing a hormonal ghost." European journal of applied physiology 112.5 (2012): 1981-1983.
• Sakashita, Maya, et al. "Oral Supplementation Using Gamma-Aminobutyric Acid and Whey Protein Improves Whole Body Fat-Free Mass in Men After Resistance Training." Journal of Clinical Medicine Research 11.6 (2019): 428-434.
• Wan, Yun, Qinghua Wang, and Gerald J. Prud’homme. "GABAergic system in the endocrine pancreas: a new target for diabetes treatment." Diabetes, metabolic syndrome and obesity: targets and therapy 8 (2015): 79.
• West, Daniel WD, and Stuart M. Phillips. "Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training." European journal of applied physiology 112.7 (2012): 2693-2702.
• Yamatsu, Atsushi, et al. "Effect of oral γ-aminobutyric acid (GABA) administration on sleep and its absorption in humans." Food science and biotechnology 25.2 (2016): 547-551.

Beta-Alanine, Widely Used, but Rarely Tested for Safety!? Individual Studies Find Serum / Muscle Taurine is Reduced by >20%, However the Totality of Evidence Suggests...

Reductions in muscle and especially serum taurine have indeed also been observed in humans, but the fact that they do not occur in lower dose studies and cannot be observed consistently in studies using higher dosages (6g) suggests that they shouldn't be a problem for the average BA user.

Regular SuppVersity readers will be familiar with the way(s) in which taurine (#TAU) and beta-alanine seem to both complement and antagonize each other. Beta-alanine, in particular, has been found to deplete muscular (and other tissue) taurine stores - a problem, generations of scientists have used to study the ill health effects of taurine-deficiency.

While studies have never reported clinical taurine depletion in response to beta-alanine supplements, we have to consider the possibility that ...

If it works (no runs + high intensity+volume exercise) bicarbonate is the king of H+buffers:

Caffeine + Bicarb Make Champions

Bicarb + Asp = Muscle Magic!?

NaCHO3 & Leg Days're a Breeze

+100% Anaerobic Endurance

Bicarb Buffers Creatine

Instant 14% HIIT Boost

... the corresponding studies (a) were not long enough in duration, didn't use (b) the same crazy amounts of beta-alanine (#BA) of which I am sure that some bros out there are taking it and (c) - most importantly - won't manifest before literally the last taurine molecules have been bumped by BA.

Note: A possible lack of histidine to recombine w/ BA is probably not a problem given the high protein intakes of the average beta-alanine supplementing athlete/gymrat.

Now, a recent study from the University of Sao Paulo (Dolan 2019) cannot fully address all of issues a-c, but the systematic risk assessment and meta-analysis can provide us with an overview of what human and animal studies that investigated an isolated, oral, β-alanine supplementation strategy can tell us so far about the following 5 safety primary outcomes

• side effects reported during longitudinal trials, 
• side effects reported during acute trials, 
• effect of supplementation on circulating health-related biomarkers, 
• effect of supplementation on skeletal muscle taurine and histidine concentration, and 
• safety-related outcomes from animal trials. 

For the analysis, the quality of evidence for outcomes was ascertained using the Grading of Recommendations Assessment Development and Evaluation (GRADE) framework, and all quantitative data were meta-analyzed using multilevel models grounded in Bayesian principles.
The first at least somewhat surprising result in Dolan et al.'s recently published paper  (2019) is the mere number of studies they came up with:

101 human and 50 animal studies were included in the study. Tingling was the only persistently reported "side effect".

Much less to anyone's surprise who has ever felt "the tingles", paraesthesia was the most commonly reported side effect of oral BA supplementation. With an 8.9-fold increase in odds of "tingling" and a crazy variability [95% credible interval (CrI): 2.2, 32.6] this odd feeling was - and that's good news - also the only reported side effect.

Taurine deficiency: If you're asking yourself why you should care about taurine deficiency, the following list of possible consequence may come handy: impaired vision, central nervous system and cardiac function; reduced bile flow, hence impaired fat digestion, and high blood lipids, impaired metabolism and elimination of toxins; reduced antioxidant defenses; impaired passage of sodium, potassium and possibly calcium and magnesium ions into and out of cells, immune imbalances; reduced muscular performance, etc.

This observation is in line with the lack of differences in terms of the participants' dropout rates when the scientists compared the active (#BA) to the placebo (#PLA) treatment; the tingles are, after all, not that bad and have been avoided in many trials by supplementation timing BA with foods and/or splitting larger into multiple smaller dosages to avoid that they would be messing with blinding the study participants to the treatment (BA or PLA).

As far as common "safety markers" are concerned, β-Alanine supplementation caused a small increase in circulating alanine aminotransferase concentration (#ALT | effect size, ES: 0.274, CrI: 0.04, 0.527), although mean data remained well within clinical reference ranges. 

The small increase in ALT is not a problem - exercise alone will increase it much more as you've learned here. 

Now, while this sounds problematic, ALT is eventually just an enzyme that metabolizes alanine, and - as I explained in "Three Reasons Why Your Doctor May Falsely Believe Your Kidney, Liver or Heart Were Damaged" (Moussa 2015), in detail - not a valuable tool for diagnosing liver damage, in particular in athletes.

Hence, the more important, unquestionably health-relevant and, at least on my part, long-awaited result of the meta-analysis of human data is this:

The scientists found no evidence of a main effect of β-alanine supplementation on skeletal muscle taurine (ES: 0.156; 95% CrI: −0.38, 0.72) or histidine (ES: −0.15; 95% CrI: −0.64, 0.33) concentration. 

You can see a forest plot displaying the effect of β-alanine supplementation on skeletal muscle taurine concentration in humans in Figure 1. As usual, the study-specific intervals represent individual effect size estimates and sampling error, while the diamond represents the pooled estimate generated with Bayesian inference along with the 95% credible interval (95% CrI). This analysis included 83 observations (63 β-alanine/18 placebo) - in short: There's no measurable effect according to the meta-analysis at hand.

Figure 1: Even if you didn't read the rest of this article an effect size of 0.156 with confidence levels ranging from -0.38 to +0.72 should qualm your worries over the taurine depleting effects of appropriately dosed (max. 3-6g/d) beta-alanine supplements - even if individual studies such as Blancquaert et al. report >25% reductions in plasma taurine.

What about the outliers, i.e. Blancquaert et al. (2017) and Harris et al. (2010)? Well, even though both studies found potentially relevant effect sizes, the confidence intervals tell you that the effects were at least so heterogeneous that it would be stupid to argue that they provide limited but relevant evidence that there could be an issue, after all - and that's despite the fact that the statistically at best borderline significant relative reduction in plasma and muscle taurine (p = 0.063 and p = 0.156, respectively) Blanquaert et al. observed was quite large, i.e. -25% in plasma and -13% in skeletal muscle after 23 days on a rather high dose of beta-alanine of 6g/day (see data in Figure 2).

Figure 2: If the Blancquaert human study, the data of which I've used to calculate the relative change in plasma (blue) and muscle (orange) levels of beta-alanine, histidine, and taurine in response to 6g/d of beta-alanine, was the only study we had, it may provide reason for concern... not just for taurine, but even more so for histidine of which the subjects in the BA group consumed a relatively normal amount of 2.1g/d.

So there is reason to worry - at least for people who can't live without worries? Well, as previously hinted at, rodent studies clearly demonstrate that overdoing it on beta-alanine can deplete your taurine levels. However, to achieve a significant reduction of taurine the minimal "daily dose was ≥3% β-alanine in drinking water" (Dolan 2019). The human equivalent of this dosage may mirror the practice of some bros who still believe in the "more helps more"-principle, but the totality of the evidence seems to suggest that within the recommended dosing scheme of 3-6g/d issues w/ local or systemic taurine deficiency shouldn't be an issue... in the short run: long-term studies (years vs. days and months) are imho still warranted.

Looking for what in theory should be the optimal H+-buffer stack? Look no further! Simply (re)view my 2018 article on #BA + #bicarbonate | more

So, what's the verdict then? Within commonly applied (performance enhancing) dosing schemes of 1.5-6-5g/d beta-alanine (#BA) is likely to cause the tingles (if administered as a bolus). Moreover, BA could trigger small and physiologically irrelevant increases in the alanine-metabolizing (liver-) enzyme ALT (learn more about those and how the enzyme is by no means liver-specific, here). The depletion of your cellular taurine stores, on the other hand, doesn't seem to be an issue if you don't dose your supplements based on bro-logic, i.e. "if some's good more is going to get me even more jacked!".

In other words, potentially serious side effects due to the depletion of taurine (and/or histidine, which is even more unlikely given the overall high protein intakes of the average BA consumer) must be feared only by those morons among you whose daily beta-alanine intake is more than 10 times the regular human dose of ~3-6g/d | Comment on Facebook!

References:

• Blancquaert, Laura, et al. "Effects of histidine and β-alanine supplementation on human muscle carnosine storage." Med Sci Sports Exerc 49.3 (2017): 602-609.
• Dolan, Eimear, et al. "A Systematic Risk Assessment and Meta-Analysis on the Use of Oral β-Alanine Supplementation." Advances in Nutrition (2019).
• Harris, Roger C., et al. "Simultaneous Changes In Muscle Carnosine and Taurine During and Following Supplementation with b-alanine." Medicine & Science in Sports & Exercise 42.5 (2010): 107.
• Saunders, Bryan, et al. "24-Week β-alanine ingestion does not affect muscle taurine or clinical blood parameters in healthy males." European journal of nutrition (2018): 1-9.