Intermittent Fasting for Muscle Growth Pros And Cons

ProSource Research Update

If you want to gain muscle mass, you have to eat. And then eat some more.

That's been the golden rule of muscle building since the rulebook was written. Fasting of any sort, whether it's accidental or (god forbid!) intentional, is to be avoided at all costs. Athletes seeking to add muscle follow a tried-and-true regimen of consuming six clean, protein-heavy meals per day to keep the engines of muscle increase firing on all cylinders. Heck, some bodybuilding fanatics set an alarm for the middle of the night so they can eat while they sleep, too. Why? Because slipping into a caloric deficit, no matter how brief in duration,  leads inevitably to decreases in protein synthesis and muscle repair that in turn lead to muscle mass loss.

Or does it?

Fasting has its place in the fitness and physique world, of course. But it has most commonly been associated with weight loss or, perhaps, a cutting phase. In recent years, fasting -- in the form of intermittent fasting -- has accrued a sizable group of devout followers enamored with the method's effects on belly fat, short-term metabolism, insulin secretion, and hormone regulation. It has even been associated with better brain health and (maybe) expanded lifespan.

Muscle builders have been slower to come around, however, partly because of the counterintuitive notion of starving for muscle and partly because, while there have been peer-reviewed studies associating intermittent fasting with weight loss, there has been little documented science to support its effect on muscle support. Until now.

Yes, that's right. The first such study -- performed on actual resistenace-trained athletes and published in the Journal of Translational Medicine -- has appeared and it has yielded some fascinating results. Before we get to that research though, let's consider the current scientific consensus on intermittent fasting -- its benefits and drawbacks.

A Boon to Dieters And a Bane to Muscle Builders?

Dieting, as we all know, burns muscle as well as fat. The weight lost during a typical regimen of extended caloric deprivation will consist of 70% fat and 30% muscle mass.



But intermittent fasting, which shortens the interval of caloric deprivation that can lead to muscle loss, may provide benefits unique to muscle preservation. When we speak of intermittent fasting, by the way, we should say that there are different methods of intermittent fasting. Some people choose the 16/8 Method, which entails skipping breakfast each day and eating during a later 8-hour window, while others favor an Eat-Stop-Eat approach consisting of one or two 24-hour fasts per week. There is also the 5:2 Diet, where people eat 500 to 600 calories two days per week, and eat normally otherwise.

So, what are the benefits? Research suggests that intermittent dieting may actually boost your metabolism over the short term, though longer fasts (anything over 24 hours) will certainly suppress metabolic rate. Intermittent dieting has also been associated with increased insulin sensitivity during fasted exercise and increased production of human growth hormone (HGH). The nervous system may also react to short periods of fasting by sending norepinephrine to fat cells, resulting in the breakdown of body fat into fatty free acids that can be utilized for energy.

All of which is good for dieters, obviously. And any improvement in fat utilization for energy will ramp up performance and make for more productive workouts, which in turn will augment muscle mass over time. But how does this confluence of physiological reactions impact muscle tissue specifically? Well, in one study, published in the journal Obesity Review, subjects experienced either consistent caloric reduction or intermittent caloric reduction for periods of 3 to 12 weeks. The intermittent restriction subjects manifested slightly less weight loss (4-8% as opposed to 5-8% for the consistent subjects) but also experienced much less fat-free muscle mass loss (.55 lb per week compared to 1.65 lb).


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Note that above we mentioned intermittent fasting's effect on hormone production. Athletes engaged in high-intensity exercise or in strenuous competition are always incentivized to keep their growth hormone and free testosterone levels in the normal range or higher by any natural means possible. (Natural means, folks, not artificial means!) Healthy GH and T levels are the foundation for a laundry list of positive outcomes for males athletes, including sexual health, exercise recovery, muscle mass increase, and overall wellness and vitality. This potential benefit of intermittent fasting alone has been sufficient to cause some athletes to question the status quo about fasting and muscle mass maintenance in recent years.

On the other hand, not consuming sufficient protein will result in a negative nitrogen balance, which in turn will result in the breakdown of muscle tissue and the inhibition of muscle growth. Even if you pile on the protein during non-fasting periods, there is also the issue of how much protein you can assimilate at any one meal.


So which is it? Does intermittent fasting help or hinder muscle support? Some people believe that the benefits outweigh the potential negatives. Up until recently, though, there has been little science to refer to, as no one has measured the effects of intermittent fasting on strength and body composition on trained athletes specifically. But now, as we mentioned earlier, someone has.

New Study: The Effects of Intermittent
Fasting on Body Composition and Strength

In the study, male subjects in the late 20s and early 30s (all with at least 5 years of training experience) were randomized into extended caloric-restrictive dieting and intermittent fasting groups. Both groups had adequate protein intake to support intensive training. All of the subjects trained three times per week and the study lasted eight weeks. At the end, the intermittent fasting group subjects lost about 1.6kg (about 3.5lbs) of fat versus a nonsignificant loss in the normal dieting group. On a hormonal level, intermittent fasting subjects experienced slightly decreased testosterone and IGF-1 levels, decreased levels of several pro-inflammatory cytokines, increased cortisol levels, decreased insulin and blood glucose levels, and decreased triglyceride levels. These results would appear to undermine the notion that intermittent fasting provides any hormonal benefit consistent with muscle mass support. Most importantly, all other factors relating to strength and body composition was basically identical between the groups.


Although the fat-loss results of that study are interesting, the remaining results hardly offer rousing support for those pursuing an intermittent fasting route to muscle mass gain. However, we believe that much more conclusive investigation remains to be done before the case is settled. Every physique reacts uniquely to different stimuli. If you were to incorporate intermittent fasting into your regimen, we would suggest that you at least slip some calorie-neutral BCAA supplementation into your fasting window to help support protein synthesis and recovery during your journey into the no-calorie wasteland.

Varady KA. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obes Rev. 2011 Jul;12(7):e593-601. doi: 10.1111/j.1467-789X.2011.00873.x. Epub 2011 Mar 17.

Tatiana Moro, Grant Tinsley, Antonino Bianco, Giuseppe Marcolin, Quirico Francesco Pacelli, Giuseppe Battaglia, Antonio Palma, Paulo Gentil, Marco Neri and Antonio Paoli. 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, 10.1186/s12967-016-1044-0, 13 October 2016.


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