Wednesday, January 30, 2013

Fasted Cardio & Beyond - Optimal 24h Fatty Oxidation: How It Works, Why It Works & Why It Still May Not Be Worth It

Photo of a typical disciple of the cult of the "fat burning zone".
Day 3 of the SuppVersity Exercise Science Week and for some of you maybe about time to have breakfast... hold on, breakfast? But shouldn't you work out before breakfast? I mean this whole cardio in the morning business you have taken up lately is all about doing it before, not after breakfast isn't it? You grab your WIFI-connected iPhone tune in to the Super Human Radio morning cardio mash-up and hop onto your cycle ergometer, treadmill, rowing machine, elliptical, spinning bike, stepper, or whatever else you may be using  - no breakfast no intra-workout supplement - at least no carbs, right? Ah, and of course you are going to work out at the highest intensity possible, to burn more fat later on, after all, you are no disciple of the cult of the "fat burning zone", right? Right! And still you have your doubts, hah?

Now, I can't tell you whether the above has anything to do with your morning routine. What I can tell you, however, are the long and short on 24h energy expenditure by summarizing and expanding on some of the main findings of a recent paper by Kaito Iwayama and Kumpei Tokuyama, two young scientists from the Graduate School of Comprehensive Human Science at the University of Tsukuba (Iwayama. 2012). 

Let's start with the "short", then

I guess you will be familiar with the term "metabolic chamber". That's a small room, where you, as a scientists, lock your subjects up in order to monitor their energy metabolism with your fancy electronic equipment and analytical methods for a prolonged period of time (usually 24h). As Iwayama and Tokuyama point out in their latest paper this technique has long been and in fact still is considered the gold standard as far as 24h energy expenditure measurements are concerned.
"During the last 10 years, experiments with this method have raised interesting observations such as: 1) exercise intensity has no effect on 24 h fat oxidation, 2) exercise has little, if any, effect on 24 h fat oxidation, and 3) exercise before breakfast increases 24 h fat oxidation."
Just in case you are one of those guys / gals who don't read quotations, we are going to spend the major part of today's contribution to the SuppVersity Exercise Science Week recapping what "the short" is telling us about your morning, afternoon and/or evening efforts to lose body fat and extend it into "the long" by adding references an examples, so don't worry.

I. Exercise intensity has no effect on 24 h fat oxidation

If you really want to maximize fatty acid oxidation while do a HIIT session before  a lengthy steady state aerobics.You should be aware though, that we are talking about relative increases, here (read more)
We all know that the amount of energy your body consumes during physical activity will depend on the "workload", which is defined as the mathematical product of force x way. In that, the force during a lift would be gravity g x mass of your weight. For a 10kg weight, this would yield a force of 100N[ewton], let's say you lift that weight from the ground into a hight of 1m. In that case, the workload you applied would equal 100N x 1m = 100Nm. If you move a larger weight, say 20kg, for example you would have done twice as much work... it's as easy as that, but unfortunately pretty useless when it is applied to the human human body. While it may still make sense to compare "work-matched" workouts with each other, the outcome in terms of the energetic demands a "10,000Nm bodybuilding workout" will produce, is very different from that of a "10,000Nm O-lifting workout", let alone a "10,000Nm marathon run". The relation between work and energy physicists often try to explain by stating that "(mechanical) energy is a measure of the ability to do work" is too simplistic to work (all puns intended) out in exercise physiology.

If we had a phyiscal model that described what happens in your body down to the level of the individual cell, things would be different. Currently, however, we are missing 99% of that model, so that we have to find other ways to measure the exercise induced and basal energy expenditure - and this is where the metabolic chamber comes in. It allows scientists to measure the energy expenditure independent of any workload calculations and does even allow for a quantitative estimation of where that energy is coming from, namely from fats or carbohydrates (and glyconeogensis). From previous studies, which availed themselves of this amazing piece of equipment, we know already that
  • for low-intensity exercise, below 40-50% of the VO2Max the energy supplied is primarily from oxidation of plasma free fatty acids
  • for intensities ranging from 50% to 95% of the VO2Max, the ratio of glucose to fatty acid oxidation, the so called respiratory rate is constantly increasing; in that, a RER of 0.8 tells us that we are fuelling 80% of our energy demands from glucose, already 
  • for intensities in the 100% of VO2max range, the RER approaches 1.0 meaning that our bodies satisfy almost 100% of their energetic demands by the oxidation of carbohydrates (glycogen => glucose)
This has, as we have already seen in yesterday's 2nd post in the SuppVersity Exercise Science Week, led to the commonly held belief that low-intensity exercise would be better than high-intensity exercise for increasing fat oxidation and, thus, fat loss (Hill. 1992).

The notion that what happens after your workout is about as, if not more important than the energy, let alone fatty acid expenditure during a workout has unfortunately not reached public awareness, as of yet.

That's a pitty, right? Well at least as far as the rate of fatty oxidation is concerned, I would not be too sure about that, as previous studies suggested that the amount of fat that's oxidized in the post-exercise recovery period following isocaloric exercise performed at high (65% VO2max for 1 h) or moderate intensity (45% VO2 max for 86-89 min) is identical!
"First, consistent with the literature, fat oxidation during exercise was less for high-intensity exercise than for low-intensity exercise. Second, the increase in fat oxidation during the post-exercise period seemed to be greater after high-intensity exercise, although the difference did not reach statistical significance. Third, the sum of fat oxidation during the exercise and post-exercise periods was not significantly different between the two exercise conditions of different intensity." (Iwayama. 2012)
Aside from these fundamental insights, the studies on which this rationale is based on did also provide another intriguing, yet somewhat discriminating insight:
  • While women have the edge as far as intra-workout fatty acid oxidation is concerned, their ability to burn fat during rest is low compared to their male counterparts (Hanerson. 2007). According to Iwayama and Tokuyama, this biological fact may also explain why women are typically less successful in achieving their fat loss goals in response to exercise only interventions than men (Ballor. 1991; Donnelly. 2005).
Now think about this for just a second, take a look at the data in figure 1 and now tell me: "What's the best way for women to maximize fatty acid oxidation?"
Figure 1: Fatty acid oxidation in male and female subjects in the 24h period after low /40%VO2Max) and high (70% VO2Max) intensity workouts with a matched energy expenditure of 400kcal; the data was measured in a metabolic chamber by Melanson et al. ten years ago (Melanson. 2002)
Right! That's low intensity long duration workouts. Those will allow them to burn more fat (on a relative basis) during the workout without experiencing the bump in post-exercise fatty oxidation rates Melanson et al. observed in their 2002 study. And yet, neither I nor the researchers who wrote...
“Given that time is a limiting factor for most individuals, if the goal of exercise is to maximize fat oxidation to better regulate body fat mass, then exercise should be performed at the highest intensity that can be comfortably maintained.” (Melanson: 2002)
...would recommend that our female or male readers stick to "training in the zone", only. You will learn why this is the case later in the article. For the moment, I do yet want to address the second and third assertion from the initially cited three-item list, first.

II. Whether you exercise or not has no influence on 24h fatty acid expenditure

At first sight this sounds, bullocks. I mean, it should be out of question that you burn more fat, when you work out, than when you lie around on the couch, right? And in this case you are right - at least, if you include the additional fatty acid oxidation during the workout in your calculation and discard things like standard deviations and statistical non-significance.

Table 1: Independent effects of exercise intensity (low vs high intensity) and exercise itself (control vs exercise) on 24h fat oxidation have been assessed under energy-balanced study design (except for the Lausanne
study, in which subjects were in a state of negative energy balance); "no" denotes not significantly different (Iwayama. 2012)
And still, under "macronutrient-balanced condition[s"], which are a necessary prerequisite to measure the independent effect exercise has on 24-h fat oxidation without having a negative energy balance or the ingestion of some sugary intra-workout drinks skew the results towards higher, respectively lower rates of fatty acid oxidation (cf. Bielinski. 1985; Dionne. 1999).  Exactly this is what has been done in a series of metabolic chamber experiments, Iwayama and Tokuyama reference in their paper (see table 1) to support their assertion that
"fat oxidation on days with exercise doesn’t differ from sedentary control days when the energy balance is maintained." (Iwayama. 2012)
While the results are anonymous it's clear that they do not support the notion that working out would exert an independent effect on the amount of fatty acids that are "burnt" within the same 24h period the exercise bout was conducted in.

Still, as Iwayama and Tokuyama point out, "statistically not significant" does not equate non-existent. You just have to take another look at the data from the Melanson study in figure 1 to see that there is a definitive trend towards increased fatty acid oxidation in the exercise compared to the control condition.

The difference between significant findings and "unreliable" trends reminds me of a previously not mentioned, yet potentially significant disadvantage of an otherwise highly reliable method to measure the total energy expenditure of human beings: The restricted number of participants in studies using indirect calorimetry with a room-sized respiratory chamber. The "trend" in the Melanson study, for example could well have reached statistical significance with a greater number of study participants; and the same obviously goes for the rest of the studies in table 1, as well. Still, as we are going to see in the conclusion, an over-reliance on statistics is not the only reason why "not working out" is not an option. Before we tackle that, I do yet want to address the last point on our check-list.

Exercise before breakfast increases 24h fat oxidation
 
This third and last of the initially cited assertions does not only take us back to the "breakfast problem" from the introduction, it's also the only assertion that's in accordance with the mainstream understanding of the role of exercise in the process of fatty acid oxidation. "Working out on empty", "cardio in the morning" and so on and so forth - you know the whole spiel and actually you do also know the scientific explanation of why working out like this does actually work out. No idea? Well, I did provide part of the explanation in the previous paragraph, already, when I mentioned the potential impact of fasting and feasting on the experimental results.
Gluconeogenic as most of them may be, EAAs still increase GLUT-4 and thus glucose uptake by the muscle - a true yet overlooked nutrient partitioner, so to say (read more)
Did you know that the two essential L's, i.e. leucine and lysine are the only amino acids that cannot be used for glyconeogenesis by the liver? Contrary to the rest of the pack, they are exclusively ketogenic and can only be transformed into ketone bodies.

In view of the built-in glucose repartitioning effect of essential amino acids (EAA), this is yet no reason to be worried about... well, unless you are on a ketogenic diet and make the standard mistake of each and every fitness fanatic to turn a high fat diet into a high protein diet without carbohydrates, so that you end up living on the little glucose your liver is able to produce without ever getting even close to real ketosis.
I see it dawns on you: It's the sheer necessity of burning fat for fuel, in the absence of other, more readily available nutrients like carbs, or glucose the liver would generate from proteins or aminos, for example. So, in the course of your workout you are actually burning more fat than you would if you had breakfast before hopping onto the treadmill, bike or elliptical, but what about the time thereafter?
Figure 2: 24h energy expenditure and fatty acid oxidation (both in kcal/min) on days on which cardio (60min 50% VO2max light steady state) was done before (filled circles) or after (open circles); data based on an unpublished from the same group (Shimada. unpublished)
As the data in figure 2 tells you, there is no difference in the following hours and - what's even more important - the total energy expenditure was identical - 2594kcal/day vs. 2589kcal/day in the before and after breakfast trial, respectively. In addition to that, a detailed analysis of the unpublished study by Shimada et al. the above data was taken from, does also show that
  • working out before breakfast reduces the energy expenditure in the time before lunch --  over the whole period the subjects burned about 500 kcal less, when exercise was performed before breakfast
  • working out before breakfast burns more glycogen and increases non-oxidative carbohydrate storage during / after breakfast -- with the carbohydrate content of the breakfast being used for glycogen repletion, this does in fact lead to another increase in fatty acid oxidation, simply because the alternative fuel, namely the carbs are not oxidized, but stored
So, 2x thumbs up for cardio before breakfast - at least in the short run and when your goal is to maximize fatty acid oxidation, but ...

Is maximal fatty acid oxidation even what you should be aiming for during a workout?

I guess you will already have read between the previous lines that my answer to this question is a definitive "no". Moreover, most of you are so clever and have been following the SuppVersity posts for so long that they could come up with their own arguments against an overemphasis of intra-, post and total 24h fatty acid oxidation, when getting lean and healthy is your goal. And probably, some of them are even identical to mine:
  • Firstly, and most importantly, burning fatty acids for fuel does not equate fat loss. If you follow a real ketogenic diet (not one with tons of protein in it), you'll burn (almost) exclusively fat, but even under these "extreme" conditions most of the fat will come from the fat you eat, while the small amount that's actually taken from your hips, buttocks and whatever, will be restored unless you are in a caloric deficit, when your fatty acid oxidation will increase anyways.
  • The "Fat Loss Support Routine" from the Step By Step to Your own Workout Routine guide would be one example of how you can structure your weekly workout regimen to cut body fat.
    Secondly, many of the metabolic benefits of exercise are closely related to the act of glycogen depletion. This is particularly true for the increase in GLUT-4 expression and consequent improvements in muscular glucose uptake, burning only fat for fuel during a workout is thus a questionable ideal.
  • Thirdly, working out "in the zone" may burn the most fat but won't have the conditioning effects high(er) intensity workouts have. While obese individuals and people who have been sitting around their whole lives will see improvements in their VO2max (and in the long run their heart-health), anyone who is not totally unconditioned misses out on the structural changes in the musculature, and as you've learned on day one of the SuppVersity Exercise Science Week adipose tissue, as well.
In short, the importance of burning fat for fuel is so overrated that exercise prescriptions that are based on the paradigm of maximal fatty acid oxidation are at least suboptimal for health, fitness and physique purposes. Some people, I guess, would probably even go so far to say that they do more harm than good. I for my part leave it up do you to decide whether you join sides with my carefully worded or the more extreme version of this conclusion, or - and this would be your good right - to wholeheartedly disagree with both of them.

References:
  • Ballor DL, RE Keesey. A meta-analysis of the factors affecting exercise-induced changes in body mass, fat mass and fat-free mass in males and females. Int J Obes. 191; 15: 717-726.
  • Bielinski R, Schutz Y, J√©quier E. Energy metabolism during the postexercise recovery in man. Am J Clin Nutr. 1985;42: 69-82.
  • Dionne I, Van Vugt S, Tremblay A. Postexercise macro-nutrient oxidation : a factor dependent on postexercise mac-ronutrient intake. Am J Clin Nutr69: 927-930.
  • Donnelly JE, Smith BK. Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences. Exerc Sport Sci Rev. 2005; 33: 169-174.
  • Henderson GC, Fattor JA, Horninig MA, Faghihnia N, Johnson ML, Mau TL, Luke-Zeitoun M, Brooks GA. Lipolysis and fatty acid metabolism in men and women during the postexercise recovery period. J Physiol. 2007; 584: 963-981
  • Hill JO. 1992. Physical activity and energy expenditure pro-ceedings: national task force on prevention and treatment of obesity. Physical activity and obesity conference – NIDDK, pp.60-65.
  • Iwayama K, Tokuyama K. Exercise in a metabolic chamber - Effects of exercise on 24 h fat oxidation. J Phys Fitness Sports Med. 2012; 1(2): 307-316.
  • Melanson EL, Sharp TE, Seagle HM, Horton TJ, Do-nahoo WT, Grunwald GK, Hamilton JT, Hill JP. Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation. J Appl Physiol. 2002; 92: 1045-1052 
  • Shimada K, Yamamoto Y, Iwayama K, Nakamura K, Ya-maguchi S, Hibi M, Nabekura Y, Tokuyama T (unpublished observation).

26 comments:

  1. I believe morning fasted cardio has its place, especially when trying to burn through the stubborn lower ab fat. But of course, this does not apply to 99% of people and a calorie deficit will be the ultimate determiner of fat loss.

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    1. well you could actually make a point saying that only when you are in a caloric deficit, making use of techniques to increase fatty oxidation makes sense. Under these circumstances specifically during fasting periods, by the way

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  2. And surely, for most people the best time to exercise is when you can! I find it easy to do cardio in the morning before breakfast - cool in summer and less distractions. If my body let me I'd do early morning weights as well but alas my decrepitude these days precludes that.

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    1. 100% agree - practicability alone would have me do it, even if it did not apparently have a minimal edge

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  3. "for low-intensity exercise, below 40-50% of the VO2Max the energy supplied is primarily from oxidation of plasma free fatty acids
    for intensities ranging from 50% to 95% of the VO2Max, the ratio of glucose to fatty acid oxidation, the so called respiratory rate is constantly increasing;"

    The percentage is less important, if the actual values for fat burn, are bigger for intense workout.

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  4. Dr. A I've been reading all your articles for about 5-6 months and have never seen you make mention of this "well, unless you are on a ketogenic diet and make the standard mistake of each and every fitness fanatic to turn a high fat diet into a high protein diet without carbohydrates, so that you end up living on the little glucose your liver is able to produce without ever getting even close to real ketosis." Could you please expound on this or perhaps suggest some article titles to search for.

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    1. He is referring to ketogenic diets (when your body relies on ketone bodies produced by ingested fats to primarily fuel the brain). The fat spares protein for being used for gluconeogenesis because the other source of glucose your brain, carbohydrates, are also low.

      However, too many people make ketogenic diets into high protein diets instead. Rather than relying on fat for ketone bodies, the high protein serves as a precursor for gluconeogenesis and thus glucose. So much so, that they don't reach a true ketogenic state and adapt to fat, but instead protein becomes a fuel for glucose.

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    2. To expand on what JP said, there are at least 4 distinct fuel sources that your body can use: glucose, protein, free fatty acids (FFA), and ketones. In general, tissues of the body will use a given fuel in proportion to its concentration in the bloodstream.

      Glucose is the preferred fuel for most tissues of the body. However, when glucose is restricted (as in the initial days of a ketogenic diet or fasting), the body will break down protein to produce glucose. However, after the initial couple of days to *adjust* the body will begin to derive its fuel from FFA and ketones. This is where the problem arises.

      If glucose requirements go down because of an increase in alternative fuels such as FFA and ketones, the need for gluconeogenesis from protein will also decrease.

      Back to the problem, about 58% of dietary protein will appear in the bloodstream as glucose (most notably alanine and glutamine), thus raising insulin (this is why protein has an insulin response btw) and inhibiting ketosis. Thus, protein must be restricted to some degree on a ketogenic diet as excessive protein intake will produce too much glucose, impairing or preventing ketosis.

      So essentially, in the initial about 3 days of going low-carb you should moderate protein intake as well. It is during this transition stage that your body revs up ketone production and reliance on FFA for fuel. However, it will still *crave* glucose during this transition period, and will break down excess dietary protein into glucose to satisfy this want. However, this inhibits ketone production, and you still eat low-carb, so your body becomes stuck in the transition phase.

      Hope this makes sense!

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    3. Thanks guys yeah makes total sense. I guess I should have made my question more specific. Have you all seen any insight as to what would be considered "high" or too much protein. I essentially stick to the 1g per pound lean body mass methodology because that amount is commonly consider muscle sparing but I've been recently reading where that number can be significantly scaled back especially with the goal of fat loss and appropriate training volume.

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    4. During the first weeks of ketosis, approximately 75g of glucose must be produced to satisfy the brain's requirements of about 100g (the other 25g is glucose coming from the conversion of glycerol). After about 3 weeks of ketosis, the brain's requirement for glucose drops to about 40g/day (because of increased reliance on ketones). Of this, 18g comes from glycerol, leaving 25g that must come from gluconeogenesis of protein.

      Assuming 58% of protein will appear in the bloodstream as glucose, and also assuming zero carbohydrate intake, you should consume a minimum of 150g of protein regardless of bodyweight during the initial 3 weeks of ketosis, after which 50g/day should be sufficient. Note that this is only to achieve nitrogen balance and exercise will increase protein requirements. Furthermore, any carbohydrates you consume (including those from veggies) will lower the protein requirement.

      1g/lb LBM is the best starting point, regardless of diet or goals. Without knowing anything else about you or your exercise/lifestyle habits, you could lower the amount of protein and see if fat-loss accelerates, but I definitely see no reason to eat more than that amount.

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    5. I am not sure about the exact amount in grams, but I can guarantee that 1g/lbs is borderline.

      Let's assume you are 80kg that would be 160g, i.e. 640kcal. If you consume ~2,500kcal on a daily basis that would be >25% and thus be beyond the already generous limit Phinney prescribes in this paper => http://www.ncbi.nlm.nih.gov/pmc/articles/PMC524027/

      in general, you will probably still produce some ketones, but "ketosis" means running on keton bodies only - your approach may still have you run majorly on ketones, but what I am seeing out there on the web with protein intakes of 200-300g and more on "protein only + some essential fat" diets has nothing to do with a "ketogenic diet". That's rather an "ammoniagenic" diet, which will flood your system with ammonia, till your liver aches and your brain stops working (I guess for some who still believe you can live on protein only that already happened ;-)

      also, did you see any benefits of your ketogenic diet as of now, John?

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    6. I completely agree that it is not a ketogenic diet. I believe the term for a protein only + some EFAs is a PSMF (protein-sparring modified fast)

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    7. Yes, basically I've been at a sticking point for several months of a somewhat ketogenic diet. My daily diet I shoot for <30 g carbs and that is entirely vegetable sourced. Typically eat grass fed red meats (beef / lamb) shooting to equate the protein content of my meat to be g per lbm and making no real effort to avoid fat. typically this is all ingested in two meals starting at lunch (don't have any hunger for breakfast time meal). Whey isolate supplementation if I don't get enough protein from meat. Typically I'll perform a weekly low fat carb refeed afternoon.

      Primalkid the most popular write up (if you will) of PSMF comes from Lyle McDonald in his Rapid Fat Loss Handbook. Pretty aggressive stuff and he suggests an EC stack to help keep BMR high

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    8. Oh, believe me, I know ;)

      I am a huge fan of Lyle, and I have done both the Rapid Fat Loss Diet and Ultimate Diet 2.0. Also the EC stack isn't so much to keep BMR high (ephedrine might boost it by 5% max). Rather, it helps mobilize fatty acids through its beta-2 agonism, and also keeps appetite at bay.

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    9. the protocol per se sounds fine, but taking EC infinitely will diminish it's effect significantly; so in case you use it, use it cyclic. The same, i.e. the importance of cycles also goes for anyone who is already at a low bf level (six pack visible) and wants to improve his physique. With eating at maintenance you will maintain what you have (at best) with mini-bulk + cuts you can make further progress. And when you bulk better skip on the IFing (or at least make it an 8h window) and go for a higher carb intake

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  5. Dr Andro - Brilliant article, delighted that we (women!) are included in your research, thank you!! I am a huge fan of your research work and would love to share this article in my Health Divas blog with links to your name and website. I am sure my UK followers would really enjoy reading you - I started recently and have over 7,500 unique visitors. Look forward to keeping in touch! Best,
    Alejandra

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    1. I am happy, whenever my readers are happy and am not against "sharing", as long as this is posting an excerpt + link. If it means copy and paste the whole piece and refer to the source somewhere in the smallest font you could find, that's a no go.

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    2. Health Divas, you should also include a resources page in your blog that gives links to other blogs/websites your followers may find useful or interesting. Of course SuppVersity would be included ;-)

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  6. Thank you Dr Andro - very kind of you! I'll include an excerpt and link.

    Primalkid - I just read your profile, do you also have a regular blog?

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    1. Lol, no I do not have a blog. Perhaps in the future, but I am content with helping out Adel at the moment.

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  7. so im confused....fasted cardio DOES increase 24 hour fatty acid expenditure? or doesn't? ive read it twice and im just double confused

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    1. it does increase 24h fatty oxidation but not because it would ramp up fatty oxidation in general, but simply because you burn some more fat during the morning fasted cardio session. Don't make the mistake to confuse that with greater fat loss, though.

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  8. If you want to lose weight, you're not alone. Losing weight too quickly can be dangerous, if you are generally healthy and you're determined to drop several pounds quickly, then you should try this weight loss product this product is very effective and you can see the result in few weeks.

    ReplyDelete
  9. So the "before breakfast group" burnt 500kcal less pre-breakfast and then 500kcal more than the "after breakfast group" post-breakfast = same energy expenditure in at the end of the day, right?

    How come there was such a big difference?

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  10. It is better and fast way to reduce fat.

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