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Rethinking Glycogen & Fat Loss

Jade Teta ND, CSCS

It is common thinking in bodybuilding and athletic training circles that glycogen (stored sugar in the liver and muscle) should be maximized at all times. The theory goes something like this: intense exercise is required to progress in performance and to stimulate muscles to grow, and glycogen is required to sustain intense exercise. Therefore, you should maximize glycogen at all times especially after exercise where there is a unique window of opportunity where most extra carbohydrates will be stored as glycogen instead of fat. I agree with this theory 100% as I have used it both in myself as an athlete and bodybuilder and in my clients. However, this theory has been over applied in my opinion.

Performance, bodybuilding, or fat loss?

There is a difference between maximizing performance or building muscle and maximizing fat loss. Sure, there are strong arguments that can be made such as: “maximizing glycogen storage allows you to train harder and therefore both burn more calories and build more muscle which in the end maximizes fat loss”. I get these arguments and dont disagree entirely, I just feel it is an “over-prescribed” tool. The vast majority of people engaging in exercise are doing it specifically for fat loss and not to be bodybuilders or become bigger, faster, or stronger to compete in an athletic event. So, the question is why do fitness professionals use a “glycogen loading” centered philosophy with their fat loss clients? In my clinical experience both as a physician and personal trainer the “glycogen loading” belief system is keeping many people from burning fat.

Should we make the same recommendations for performance and fat loss?

Much of the belief and research about glycogen comes from performance studies on distance runners which clearly show those who are glycogen loaded perform better (graph D below). However, these same studies show the amount of glycogen a person has stored in their muscle and liver is inversely proportional to how much fat they burn. In other words, the more glycogen you have stored in your body the less fat you burn at rest and during a workout. The graphs below were taken from a study in 1991 by Wagenmakers, et. al. (Am J Physiology.260:E883). The red line represents subjects who were glycogen depleted (low sugar storage) and the yellow line represents subjects glycogen loaded (maximum carbohydrate in the muscle and liver). In graphs “B” & “C” you can see very clearly the difference in fat metabolism in the two groups. If you compare those graphs to graph “A” you will notice a very simple law that is all to often forgotten…..the easiest and most abundant fuel to burn is the one your body uses in exercise. In the case of glycogen loading, carbohydrate is easy to burn and excessively available, therefore it is used preferentially. While it is clear you are more likely to win a race if you are carb loaded, you will not maximize fat loss.

In addition to the ability to burn more fat during exercise, the ability to burn more fat after exercise is enhanced in a glycogen depleted state as well. Exercising in a carbohydrate depleted state has been shown to have several hormonal advantages resulting in an elevated “afterburn” (an enhanced state of calorie burning that takes place after a workout). This includes increased catecholamine production (adrenaline and noradrenaline; these are your body’s fat burning gas peddles), human growth hormone release (HGH), glucagon levels, and testosterone production. At the same time it lowers insulin a major fat storing hormone.

Studies show glycogen depleting exercise great for fat loss?

A October 2009 study by Bahadori & McCarty published in the journal Medical Hypothesis shows how effective glycogen depletion can be. In this study, participants were instructed to fast for 12 to 14 hours daily. In addition, they were instructed to engage in a “prolonged, moderate-intensity exercise session” within this fasting time period. The researchers reported the average participant did brisk walking for 60 minutes or less as their chosen exercise. The study subjects were followed for 12 weeks. At the end of the study participants lost on average 4.2kg (~ 9 lbs). Interestingly, most of the weight lost was fat. The average fat loss in the subjects was 7.4 kg (16.28 pounds). If you are confused how they lost more fat than pounds, it is likely because the participants added muscle during the study period as well. In my opinion, the results of this study are striking. Walking, while healthy, has never been shown to be an effective exercise for fat loss (fat loss= weight loss without muscle loss). The combination of fasting and the exercise together seemed to have a synergistic effect. Based on the discussion above regarding glycogen, these results seem to make good sense.

More research needs to be conducted with a much bigger sample size to further evaluate this method, but I personally have seen this technique work both in myself and my patients. The idea that glycogen should be maximized is a great idea for high performance athletes and muscle building weight lifters, but may not be ideal for fat loss seekers.

How we use it?

At Metabolic Effect and at my clinic we use this technique with certain weight loss resistant clients. To make the process easier we usually recommend the client eat their last meal between 6 and 8pm. We then have them exercise when they wake in the morning before eating any food (between 6 and 8am). We then have them eat breakfast within 2 hours of their workout. I realize many personal trainers, bodybuilders, and conditioning specialist will likely frown on this technique because of the “glycogen dogma”. However, I have found this technique to be reasonably adhered to and highly effective. It is true however that 95% of my clients are interested in fat loss. I rarely have more than 2 to 5 athletes and/or bodybuilding clients I am training at one time. This is NOT a technique I recommend for these types. One caveat is that long duration workouts (lasting over 40 minutes) especially if they are intense in nature are not tolerated well by most in this state. However, long duration light activity like walking or high intensity short duration workouts (less than 30 minutes) work very well with this technique and rarely cause difficulty.

See more on exercise and glycogen levels at my post on exercising on an empty stomach.