Artificial Sweetener Saccharin Increases Weight Gain in Rodent Study Without Increasing Food Intake | Plus: Meta-Analysis of Human Studies Says: "No Reason to Worry!"

Should you freak out about a small increase in body weight in a small-scale rodent study that is attributed to the consumption of saccharin in yogurt?

While epidemiological studies show that the consumption of products containing non-nutritive sweeteners (NNS) is associated with increased adiposity (Colditz. 1990; Fowler. 2008), type 2 diabetes mellitus (T2DM), metabolic syndrome and cardiovascular disease (Dhingra. 2007; Lutsey, Steffen. 2008). A mechanistic link between aspartame, sucralose, stevia & co and weight gain as well as its ill metabolic and cardiovascular consequences in humans is non-existent (learn more).

Rather than weight increases controlled human studies show that the consumption of artificially sweetened foods promote, not hinder the loss of body fat (Sørensen. 2014).

You can learn more about sweeteners at the SuppVersity

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Sweeteners & the Gut Microbiome Each is Diff.

Chronic Sweeten-er Intake Won't Effect Microbiome

Stevia, the Healthy Sweetener?

Sweeteners In- crease Sweet- ness Threshold

In animal models, though, the results have been more conflicting. While many studies show no effect of artificial sweetener consumption, the latest stud by Kelly Carraro Foletto and colleagues is not the first rodent study to suggest that non-nutritive sweeteners may also interfere in the regulation of compensatory appetite promoting weight gain (Davidson. 2011; Polyák. 2010; Rogers. 1988). This does yet not refute the findings of one of the latest meta-analysis of the effects of low-energy sweetener consumption on energy intake and body weight in man - a meta-analysis published in Nature's prestigious International Journal of Obesity that says...

Figure 1: The forest plots of the practically most relevant data of individual and combined effect sizes for sustained intervention studies comparing the effects on body weight of sweeteners versus sugar (upper panel) and versus water (lower panel) shows that not a single long(er) term study found negative effects - the exact opposite is the case. Even compared to water the use of low-energy sweeteners (artificial or not) lead to measurable, yet not always significant decreases in body weight in human trials (Rogers. 2015).

"that the balance of evidence indicates that use of LES [low or no energy sweeteners] in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water" (Rogers. 2015 | my emphasis).

And with respect to the often-cited "evidence" from animal and observational studies, the autors of the meta-analysis submit that...

"[...] the present review of a large and systematically identified body of evidence from human intervention studies, with varying designs, settings and populations (including children and adults, males and females, and lean, overweight and obese groups), provide no support for that view. The question then is whether those hypotheses should be rejected or whether, as seems unlikely, the relevant human intervention studies are consistently flawed in a way that leads, in most cases, to exactly the opposite outcome" (Rogers. 2015)

I do thus want to warn you: Do not overrate the already relatively small amount of extra-weight the rodents in saccharin group of Foletto's recent study gained (see Figure 2, left).

Figure 2: Cumulative weight gain and total cumulative energy intake of (only) 16 male Wistar reds fed diets that were supplemented with either saccharin-sweetened or non-sweetened yogurt added (Foletto. 2015)

In a previous study, Folleto et al. had already observed that saccharin can induce weight gain when compared with sucrose in Wistar rats despite similar total caloric intake. In their latest study they did not try to prove that this effect is independent of the rodents' energy intake and mediated by insulin-resistance and / or modified levels of leptin and PYY in the fasting state.

Was it fat they gained or lean tissue mass? Well, I would like to answer these important questions, but Foletto did not disclose (or not even measure?) this important parameter. The practical relevance and reliability of their results is further reduced due to the small cages (44x34x16 cm individual cages) into which the rodents were confined to reduce their voluntary physical activity during the 14 weeks of the experiment, as well as the exclusion of rats who didn't consume the aspired 70% of the planned 75 kcal in form of yogurt per week (the number of rats who fell into this category is also not disclosed).

To this ends, the researchers randomly assigned 16 male Wistar rats to receive ~78kcal per week from either saccharin-sweetened (0.3% saccharin) yogurt or non- sweetened yogurt (0.5 kcal/g) in addition to chow (2.93 kcal/g) and water ad lib. For 14 weeks, Foletto, et al. measured the total food intake (from yogurt and chow) daily and the weight gain on a weekly basis (the results are plotted in Figure 2). Fasting leptin, glucose, insulin, PYY and HOMA-IR levels were measured only at the end of the 14-week study period, though.

Table 1: In view of the fact that any existing negative effects of dietary sweeteners may well be compound-specific. It is certainly worth noting that saccharin is no longer used in modern sweetener formulations of sodas (Wikipedia. 2015)

In spite of the already reported ~5% increase in cumulative weight gain over 14 weeks (p=0.027), the researchers found no differences in HOMA-IR (=insulin resistance), fasting leptin or PYY levels between groups that could mechanistically explain why the rodents who received saccharin sweetened yogurt gained more weight than their peers who received non-sweetened yogurts.

Measurable weight increases are a common pattern in rodent studies particularly for the (today rarely used) artificial sweetener saccharin. It is thus well possible that any existing negative effects are compound-specific. For aspartame, for example, similar evidence is rare to non-existent.

Bottom line: In the absence of a proven theory about the mechanism that may trigger the increased weight gain and in view of the lack of health-relevant data (no information about the body composition of the rodents) and health-relevant side-effects you would usually see in response to pathologic weight gain (changes in insulin resistance, leptin or PYY), I can only refer you back to the quote from the latest meta-analysis of the effects of low- to no-energy-sweetener intake on food intake and weight gain in humans, which say that "the balance of evidence indicates that use of LES [low or no energy sweeteners] in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water" (Rogers. 2015).

Furthermore, more relevant evidence from human clinical trials supports the use of artificially sweetened foods as dieting aids (Sørensen. 2014 | learn more).

Whether that's enough to convince you that the unproven negative effects of saccharin on caloric expenditure or increases in the glucose transport mediated by gut sweet-receptors, of which Foletto et al. speculate that they may explain the results of their study, are relevant enough to avoid non-nutritive sweeteners altogether is now up to you. For me it's not enough... | Comment on Facebook!

References:

• Foletto, Kelly Carraro, et al. "Sweet taste of saccharin induces weight gain without increasing caloric intake, not related to insulin-resistance in Wistar rats." Appetite (2015).
• Rogers, P. J., et al. "Does low-energy sweetener consumption affect energy intake and body weight? A systematic review, including meta-analyses, of the evidence from human and animal studies." International Journal of Obesity (2015).
• Sørensen, Lone B., et al. "Sucrose compared with artificial sweeteners: a clinical intervention study of effects on energy intake, appetite, and energy expenditure after 10 wk of supplementation in overweight subjects." The American journal of clinical nutrition (2014): ajcn-081554.

Is »BAIBA« the Next Big Thing in Fat Loss Supplements? 24% Reduction in Fat Gain is an Impressive Number, But...

Could BIBA be the active ingredient in a pill that solves your weight problems once and for all? Or is that too good be true?

Beta-aminoisobutyric acid, aka BAIBA, is a natural catabolite of thymine. As with many other purported "next big things in fat loss supplements", early rodent studies suggest that it can significantly reduce body fatness through a mechanism that appears to involve increases in fatty acid oxidation (FAO) and reductions in de novo lipogenesis - in particular in the liver (Maisonneuve. 2003 & 2004; Begriche. 2008).

As Karima Begrich et al. point out in a more recent review of the literature, "experimental evidence [... also] suggested that BAIBA could reduce body adiposity through increased leptin expression and secretion" (Begriche. 2010).

Some people say that caffeine is the last real "fat burner" left on the market

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Against that background, it is only logical to ask whether we have overlooked a potent natural fat burner with a mechanism of cation that may be beneficial for both losing fat (increase in fat oxidation and decrease in fat storage) and keeping it off (modulation of leptin expression and secretion).

Unfortunately, it does not take long to find the first evidence that blows a hole into the neat "BAIBA could solve the diabesity epidemic"-theory. It comes right from one of the previously cited studies.
In their 2008 study, Begriche et al. were able to confirm that the provision of 100mg/kg per day (for humans that would be ~8mg/kg per day) of Beta-aminoisobutyric acid triggers significant reductions in body fat gain in lean mice (Figure 1, left).

Figure 1: 100mg/kg/day BAIBA may be an anti-weight gain supplement The data from obese rodents (rights) does yet suggest that it is not a weight loss supplement (Maisonneuve. 2004) | Anti-obesity, but not weight loss effects were also observed in obesity prone rodents in a 2008 study by Begrich et al. at the same dosage of BAIBA.

What the same amount of BAIBA did not do, though, was to prevent the weight gain in already obese mice (Figure 1, right). In view of the fact that the same discrepancies were observed for liver fat and total body weight (not shown in Figure 1), the currently available evidence clearly doesn't support the use of BAIBA as a classic "fat burner".

In obesity prone mice, BAIBA (100mg/kg) did not just ameliorate the body fat gain, it also reduced (c,d) the number of fibrotic leasons (a,b) of the liver that occured when the ob +/+ mice got fat (Begrich. 2008).

Is BAIBA even safe? In the absence of human studies that's difficult to say, but in rodents it had no ill effects on mtDNA replication (Mainonneuve. 2004) and displays a generally low toxicity. As Begrich et al. point out, their "further investigations are [still] requested to determine whether BAIBA could induce deleterious effects," even though, "it seems that this endogenous derivative could have a favourable safety profile that might be attractive for pharmacological usage" (Begrich. 2010). Deteriorations of the lipid or glucose metabolism, were not observed in any of the currently published studies and at a dosage of 100mg/kg BAIBA reduced the fibrotic leasons in the livers of obesity prone mice and improved the level of lactate dehydrogenase, a potential marker of liver problems (Begrich. 2008).

Overall, it does thus appear as if Begrich's own conclusion that BAIBA supplements "may be indeed an attractive pharmacological strategy in order to prevent (and/or treat) obesity" (Begrich. 2010) is only partly warranted:

• While BAIBA may be useful to ameliorate the body fat gain in lean individuals and would thus in fact be an "attractive pharmacological strategy in order to prevent [...] obesity" (ibid.) in an obesogenic environment,
• it appears to be more than just 'a little too early' to assume that BAIBA supplements could also be used to "treat" (ibid.) obesity in individuals who are already carrying >50% more body fat on their frame than the average lean person.

It is however more than the fact that many of you are probably (still) lean that keeps BAIBA in the game: If you look at the data in Figure 2, it becomes obvious that BAIBA may do more than to prevent the body fat gain in people who have always been lean: its effect on leptin, in particular, could be of even greater use for people who have lost a significant amount of body fat and are now struggling with the nasty yoyo effect.

Figure 2: The increase in adipocyte (=fat cell) leptin and adiponectin production that was observed in the petri dish is particularly interesting for people who have already lost a significant amount of body fat (Begrich. 2010). If it translates into in vivo human studies, it may help those people to stay lean and reverse "metabolic damage".

As you can see in Figure 2, in vitro data shows that the direct exposure of fat cells (adipocytes) of mice, which are at a particularly high risk of becoming obese, will trigger a significant increase in leptin and adiponectin production. Why's that important? Well, of these...

• 

  Metabolic Damage, Energy Intake & the Human "Energy Thermostat" - An Update Based on Recent Studies | read it!

  the increase in adiponectin that is produced by one's fat cells has been linked to important health markers, like increased insulin sensitivity and improved markers of lipid management.
• the increase in leptin production, however, may be of greater importance, because the diet- or rather fat-loss induced remodelling of the adipose tissue (many small empty fat cells) will reduce the production of the "you're fat enough" signal leptin and thus increase the risk of formerly obese individuals to regain every pound (or even more) of body fat they have painfully lost over months of hard dieting.

With that being said, the possibility that BAIBA may be able to reverse a potential cause of something that is often referred to as "metabolic damage" of which it appears as if it was at least partly triggered by a reduction in relative leptin production (i.e. the amount of leptin that is produced at a certain level of body fat) brings BAIBA back into the game. 

Bottom line: Whether an increase in leptin production is, as Figure 3 from Begrich's previously cited review suggests, the only (or at least the most important) mechanism of the beta-aminoisobutyric acid induced anti-obesity effect will yet have to be confirmed in future studies.

Figure 3: If Begrich et al. (2010) are right, the beneficial effects of BAIBA are mediated mostly, if not exclusively by leptin. Due to a lack of human data, BAIBA must - as of now - still be classified as "promising, but unproven" anti-obesity supplement.

Of even greater importance than investigations into what I would like to call the "leptin hypothesis of BAIBA's anti-obesity effects", though, is the simple confirmation of its effects in independent human studies. I mean, rodents are (often) a good model of human metabolism, but there are instances where slight metabolic differences between man and mouse can have a huge impact on several practically relevant research outcomes. It is thus well possible that unexpected human-specific "side effects" like an extreme increase in appetite and energy intake could reduce or blunt the purported anti-obesity prowess of BAIBA. Before the aforementioned human studies have not been conducted, peer-reviewed and published, I recommend to stay skeptical about BAIBA being the "next big thing in fat loss supplements." | Comment on Facebook!

References:

• Begriche, Karima, et al. "β‐Aminoisobutyric Acid Prevents Diet‐induced Obesity in Mice With Partial Leptin Deficiency." Obesity 16.9 (2008): 2053-2067.
• Begriche, Karima, Julie Massart, and Bernard Fromenty. "Effects of β‐aminoisobutyric acid on leptin production and lipid homeostasis: mechanisms and possible relevance for the prevention of obesity." Fundamental & clinical pharmacology 24.3 (2010): 269-282.
• Maisonneuve, Caroline, et al. "Mitochondrial and metabolic effects of nucleoside reverse transcriptase inhibitors (NRTIs) in mice receiving one of five single-and three dual-NRTI treatments." Antimicrobial agents and chemotherapy 47.11 (2003): 3384-3392.
• Maisonneuve, Caroline, et al. "Effects of zidovudine, stavudine and beta-aminoisobutyric acid on lipid homeostasis in mice: possible role in human fat wasting." Antiviral therapy 9.5 (2004): 801-810.

Cardio After Weights! Doing Resistance Before Endurance Training Has More Beneficial Effects on Leptin, Cortisol, Testosterone and Body Composition in Young Men

I can almost guarantee that the results of this study are not sex-specific. Ladies, pick up the weights fater you hit the treadmill, stairmaster, elliptical or other torture instrument you like to use!

It has been a while since the last study on exercise order (cardio or weights first) has been published. Now, scientists from the University of Kurdistan have conducted another study to investigate the effects of intrasession sequencing of concurrent resistance and endurance training on the serum leptin, testosterone, cortisol responses and body composition in obese men.

And don't worry, we are not talking about useless acute-phase data that shows no correlation with either strength or muscle gains, or fat loss (West. 2012). Sheikholeslami-Vatani and colleagues conducted an eight-week study on thirty obese young male students without continuous exercise history (age: 23.2±1.4 year, BMI: 31.8±1.6 kg/m²).

You can learn more about the optimal exercise order at the SuppVersity

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Exercise Order and Leptin Levels

Cardio First for Anabolism?

Large Muscle Groups First?

Combine Cardio & Strength, Right

Exercise Order Reloaded

The subjects were randomly divided into three groups: concurrent resistance-endurance (CRE, n = 10) group, concurrent endurance-resistance (CER, n = 10) group and control (C, n = 10) group (no training program). The concurrent training groups (CER and CRE) trained three times a week on alternate days for 8 weeks. The training itself consisted of which consisted of ...

"running with 70—75% of maximal heart rate (HRmax) for 10 minutes which gradually increased to 80% HRmax for 21.5 minutes [plus] resistance training consisted of 3 sets of 8 repetitions at 80% of 1 repetition maximum (1RM) in 5 resistance exercises (leg extensions, lying leg curl, triceps pushdown, bench press and lateral pull down)" (Sheikholeslami-Vatani. 2015). 

In-between the endurance and resistance (or vice versa) training parts of the workouts, the subjects rested for 5 minutes. Blood sampling and skin-fold measurements to asses the body composition was conducted 48 hours before the start of the course and again 48 hours after the last training session (learn why waiting longer for the body comp test may have been better, but no study does that).

Figure 1: Relative changes in hormone levels (left) and absolute and relative changes in body fat fat free mass and body fat % (right) after 8 weeks of doing nothing (C) or doing cardio (CER) or weights (CRE) first (Sheikholeslami-Vatani. 2015).

I've plotted the most important results in Figure 1a & b. So, let's take a look: The first thing that everyone should see is that both workout regimen had relevant health and physique effects:

• 

  Similar gains w/ weights vs. cardio first in trained men | more.

  normalization of leptin levels (health)
• slight increases in testosterone (health)
• increases in cortisol (which are benign | learn why)
• significant reductions in body fat (health + physique)
• increases in fat free mass (health and physique)

In that, the resistance training first (CER) group came off slightly better in all tested study outcomes. Statistical significant inter-group differences, however, were observed only in comparison to the control group. In view of the fact that the body fat (total and %) improvement reached statistical significance compared to control only in the endurance first, group, yet not in the strength first group, one may still argue that the difference between cardio first (CER) and weights first (CRE) was "almost significant" ;-)

Weights or Cardio? What's the Best Visceral Fat Burner + How Often, Long and Intense Do You Have to Train | Learn more!

So, weights first is the way to go? Well, I assume I should write that doing both on separate days and thus doing having 5-6 workout days per week may have even more pronounced effects on the body composition of obese young men. In the end, though, I have no evidence to prove that doing the same amount of cardio on a separate day would actually have yielded greater improvements in body composition. Against that background and in view of the fact that three workouts per week is everything that fits into the busy schedules of the average trainee, we are left with the confirmation that (a) doing (intense) cardio and weights in one session feasible and effective when the goal are health and physique improvements and that (b) if you or your clients combine both, you better start with the weights, not the cardio part | Comment!

References:

• Sheikholeslami-Vatani, D., et al. "The effect of concurrent training order on hormonal responses and body composition in obese men." Science & Sports (2015).
• 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.

The Overfeeding Overview: High Fat, Carb, Protein, MCTs, Leptin, Testosterone, T3 & Reverse T3 - Get an Overview of the Consequences of Short- & Long-Term Overfeeding

High fat + high carbohydrate foods like mini doughnuts are exactly what you should not eat on a refeed day, let alone during weeks of bulking.

Do you want to know what happens during days and weeks of gluttony? How the effects "bulking" will have on your body weight and composition, depending on where those extra calories come from? Have you wondered what the optimal nutrient composition on refeed days may look like? And are you concerned about the potential the health consequences of bulking?

Yes? In this case, I would suggest you take a closer look at the following overview of the research. An overview that is probably not complete, but it should suffice to provide preliminary answers to the aforementioned questions.

Learn more about the effects of your diet on your health at the SuppVersity

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Carbohydrate Shortage in Paleo Land

• The amount of weight you gain depends on your genes: They are not the only determinant. That's for sure. A 1990 study by Bouchard et al. still leaves no doubt that your genes are one of the most important determinants of the quantity of weight you gain.
  
  In said study the researchers from the Laval University fed 24 sedentary young male twins 1,000kcal extra for six out of seven days of the week. In that, the study is not the first to investigate the effects of overfeeding on weight gain in twins. It is yet the first and only one that did this over a period of 100 days and thus with a total energy excess of 84,000 kcal on a diet that contained 50 percent carbohydrate, 35 percent fat, and 15 percent protein.
  

  

  Figure 1: Comparison of the weight (left) and visceral fat (right) gains in twin pairs; high correlations were observed for both, but the correlation was significantly more pronounced for the unhealthy visceral fat than it was for the mere body weight (Bouchard. 1990).

  The data in Figure 1 does probably not need any extra explanations. In view of the fact that similar results have also been observed in previous studies like Poehlman et al. (1986), it should be obvious that the difference between the weight (left) and visceral fat (right) two identical twins gained was significantly smaller the difference between one twin from pair A and one twin from pair B. The statistical analysis of body fat and waist circumference data revealed similar correlations which were most significant for the visceral fat mass and the waist hip sizes, i.e. those quantities that predict the ill health effects of weight gain best.
  
  According to Ukkola, et al. (2001), the genetic differences may partly be mediated by differences in the genetic make-up of ones beta-2 adrenoreceptors with specific variants being associated with greater increases in insulin resistance, body weight, and subcutaneous fatness. Other candidates are the cholesterol ester transfer protein (CETP) gene which appears to affect adiposity in response to long-term overfeeding (Terán-García. 2008). Other scientists use similar genetic polymorphisms to explain a general resistance to weight gain during overfeeding via genetically determined variations in nonexercise activity thermogenesis (Vanltallie. 2001).
• Overfeeding fat, carbohydrate or protein, does it make a difference? Studies that compare isocaloric overfeeding are quasi-non-existent. What we do have are studies like the one by Horton et al. (1995) that compared high fat vs. high carbohydrate diets (see Figure 2 for macronutrient composition), where the additional energy came from fat or carbohydrates.
  
  In the Horton study, this was a 50% extra that was added in form of fat or carbohydrates on top of the baseline diets of the normal-weight and obese subjects. A 50% extra that leads to significant weight gain.
  

  

  Figure 3: Weight gain (left) and increase in energy expenditure (right) in obese and lean subjects in response to carbohydrate and fat overfeeding (Horton. 1995).

  As you can see in Figure 3, both diets led to a rapid increase in body weight, but the trajectory was different. The main and maybe practically relevant difference, though, was that the rapid increase in water and glycogen in the high carbohydrate group was less resilient weight loss in the post-overfeeding period.

No! Carbs are not necessarily more fattening in the obese. It's a commonly held prejudice that carbohydrates are more readily converted to fat and stored in the obese, but a study by Minehira et al. that investigated just this found that there was not just no difference in de novo lipogenesis with carbohydrate overfeeding between lean and obese individuals, there was also no increase in de novo lipogenesis, at all, when the when the obese subjects were overfed with a high carbohydrate diet for one day (Minehira. 2004).

• 

  Figure 4: Proportion of the energy that was stored as body fat (Horton. 1995).

  If we take a look at the proportion of energy that was stored as body fat in Figure 4, it is obvious why the fat gains lasted longer than the carbohydrate gains. Why? Well, simply because the 14-day overfeeding on fat lead to a significantly higher relative increase in body fat.
  
  Last but not least, it may also be worth mentioning that the fat gain in the obese group was 89% and 57% higher in the carbohydrate and fat overfeeding group, respectively. An intriguing result that appears to stand in line with dieting studies, where high-fat diets are superior to high carbohydrate diets in the obese, but not in lean individuals.
  
  What was not different for obese and lean individuals, though, was the fact that the carbohydrate overfeeding lead to higher gains in lean mass than the fat overfeeding. A result that should remind you of a previously reported study here at the SuppVersity, in which a no fat bulk lead to significantly greater muscle and significantly lower fat gains than a low-fat bulk (see "If You Go "High Carb", You Better Go Really High!" | more). Overall, "bulking", i.e. eating more than you need on any mixed diet, has repeatedly been shown to produce significant increases plasma Somatomedin-C/Insulin-like Growth Factor (SM-C/IGF-l) and testosterone concentrations as well as insulin, of which Forbes et al. speculate that they promote the lean mass increases that are particularly pronounced when overfeeding is combined with resistance training.
  
  In a more nutrient-type specific study b by Dirlewanger that did not focus on the weight gain or anabolism, but on the leptin response and the increase in resting energy expenditure the subjects experienced a significant increase in leptin (+28%) and resting energy only in the high carbohydrate, yet not in the fat overfeeding arm of their study in young, lean individuals (Dirlewanger. 2000). Other studies, without clear distinction between high carb and high fat overfeeding, indicate that fast food like burgers or fries is an effective short-term leptin stimulator, too - at least if it's consumed in a single binge (Kolaczynski,. 1996).
  

  

  Figure 5: Energy partitioning in young men upon overfeeding with ~5,000kcal per day - mostly carbohydrates, i.e. 1% protein, 3% fat, and 86% carbohydrate (Acheson. 1988).

  In the short run, like on refeed days, for example, carbohydrate overfeeding has another advantage over fat overfeeding, because it takes roughly 500g of carbohydrates (that's 2,000kcal) before even a single gram of those carbs is converted to fat and potentially, but not necessarily stored as body fat (Acheson. 1988) - at "only" 400kcal extra from carbs for one day there was no net lipogenesis at all (see Figure 5). This result is corroborated by data from McDevitt et al. (2000) who observed that the fat gain with fat overfeeding starts with day 1, while there is a time gap in the increase in body fat with carbohydrate overfeeding (McDevitt. 2000).

If you consume sugar on a refeed, should you prefer glucose, sucrose or fructose? In view of the fact that I don't suggest you refeed more than 1-2 days and considering the fact that you want to get the majority of your carbs from starches on a true bulks, it does not really matter. In fact, studies show no difference in de novo lipogenesis in 96h overfeeding studies between pure glucose and sucrose, which is a 1:1 combination of fructose or fructose in two studies in lean and obese women by (McDevitt. 2000 & 2001). In the long run, consuming amounts of fructose you could only get by drinking a couple of bottles of coke every day, will yet not be favorable for your health - even if taking fish oil can blunt the increase in hepatic de novo lipogenesis, it won't blunt the insulin resistance (Faeh. 2005).

• 

  Figure 6: Schematic representation of the main lipid metabolic pathways affected in skeletal muscle during 4 weeks of fat overfeeding. Genes indicated in white boxes were down-regulated during the dietary study, whereas genes indicated in gray boxes were up-regulated (Meugnier. 2007).

  Fat overfeeding, on the other hand, has been shown to favor fat storage not just because the dietary fat can be stored without being converted to triglycerides, but also because metabolic and genomic investigations show that the lipid oxidation rate tends to decrease, and 55 genes in the skeletal muscle were modified.
  
  Modifications of which Meugnier et al. show that they stimulate the synthesis of triacylglycerol, inhibit lipolysis and reduce the oxidation of fatty acid oxidation while promoting the development of adipocytes with an excess of only ~550kcal/day from fat per day (see Figure 6).
  
  Another potential explanation is the change in thyroid hormones, of which the data in Figure 7 from an overfeeding study by Danforth Jr., et al. (1979) tells you that the high protein overfeeding despite a 29.8% lower total energy intake triggered the most, the carbohydrate diet the 2nd most favorable (=in favor of greater energy expenditure) effects on the thyroid hormone.
  

  

  Figure 7: Effects of overfeeding with carbohydrates, fats, and protein on thyroid hormones (Danforth, Jr. 1979).

  Accordingly, high protein diets, of which we know for sure that they are the most satiating hypercaloric diets (followed by high carb and high fat | Johnstone. 1996) and have the highest thermogenic effect (see Figure 8) and can help dieters avoid the yoyo effect after a diet (Lejeune. 2005), should have the least negative impact on your physique.
  

  

  Figure 8: Estimated thermic effect of carbohydrates fats, protein, and alcohol in % energy of the energy that's ingested in form of the respective nutrients (Joosen. 2006).

  And in fact, Jose Antonio et al. (2014) have recently been able to show that a diet that contains fivefold more protein than the FDA recommends (4.4g/kg | 307g/day) is not just benign but will, in conjunction with exercise, will have significant beneficial effects on the physique of healthy resistant trained men (learn more). Furthermore, studies indicate that a high protein content may also ameliorate negative effects such as an increase in intrahepatocellular lipid deposition in humans (Bortolotti. 2009).

Beware of bulking the way you did in your twenties! It's almost certainly going to make you fat because studies indicate that age correlates with a decreased increase in energy expenditure in response to overfeeding (Roberts. 1996). Since the difference is particularly pronounced on day 1 of the respective overfeeding period (see Figure on the left), I would also refrain from excessive "refeed days" if I were 60+ years old, like the subjects in the study by Roberts et al. from which I grabbed the graph that displays the energy expenditure on a diet that contained 956kcal extra per day (phase II in this study).

• Classic overfeeding studies with protein as a single nutrient are yet unfortunately rare. Even less, namely nothing, is known about the effects of ketogenic diets, which is why it's at the moment impossible to tell whether a hypercaloric high fat diet that is devoid of carbs and low enough in protein to actually induce ketosis will have the same negative effects as a high-fat diet that still contains 15-30% carbohydrates and some protein.
  Based on the studies we have, it's yet quite certain that the combination of some carbs and a high amount of fat is the most obesogenic variety of "bulking" you could possibly select. Therefore - with the exception of ketogenic diets, where corresponding data is still missing, the rule of thumb is: The more fat in the diet, the more rapid the body fat, but not necessarily the body weight gain.

• MCT overfeeding is less obesogenic - The reason that rodents that are overfed with medium-chain triglycerides (Geliebter. 1983) and assumable human beings store less fat than on long-chain triglycerides as you will find them in your bacon, sausages, dairy & co is an increase in thermogenesis that has been observed in both rodent and human studies.
  

  

  Figure 10: Metabolic rate in healthy men after the ingestion of isocaloric fat meals containing MCTs or long chain triglycerides (Hill. 1989).

  As you can see in Figure 10, this effect does not diminish over time - at least, when only the effect of the infusion of MCTs versus long-chain fatty acids is concerned. In view of the rodent study by Geliebter et al. (1983) and the results of the study by Hill et al. (1989), it appears to be quite obvious that MCTs constitute a valuable addition to hypercaloric diets. The often-heard claim that they cannot be stored as fat is yet misleading - even if they are oxidized in the liver, the increase in available energy will increase the storage of energy from other nutrients. The dream of eating as much as you want without gaining weight does, therefore, remain a dream - at least for all of us who don't harbor a gene defect that blunts the storage of fat.
  
  Still, in theory, it would appear as if using MCTs in a dieting context makes sense. In reality, studies have shown that using MCTs as a major source of your dietary fats does not lead to significant long-term improvements in fat or general weight loss - even if 27% of an 800kcal/day starvation diet were pure MCT oil (Yost. 1989).

Fivefold More Than the FDA Allows: Extreme High Protein Diet (4.4g/kg | 307g/day) Benign & Non-Obesogenic. Plus: Macronutrient Prescription & Changes in Food Quality | more

Alright, so what's the bottom line, then? I guess, in view of the fact that we still have few studies on high protein overfeeding and no studies on overfeeding on ketogenic diet, a conclusive bottom line cannot be reached, yet. What appears to be true, though is that a diet containing some carbohydrates and large amounts of fat is the worst choice you can make when you are bulking.

A protein and a high(er) carbohydrate, as well as a correspondingly low(er) fat content, on the other hand, appear to be the way to go at least in the short run. In the long(er) run, on the other hand, the differences between higher fat and higher carbohydrate overfeeding appears to disappear - albeit with a small, but potentially practically significant difference in terms of the amount of body fat you will gain (see Figure 4) | Comment on Facebook!

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