Written by Michael J. Rudolph, Ph.D.
29 November 2018


Fast for Muscle Gains & Fat Loss

How Not Eating Can Help You Grow


Let me first explain how the evolutionary analysis of muscle growth supports the use of this nutritional strategy for gaining muscle size. Early humans, living around 100,000 years ago, expended a lot of energy hunting for food. The complexities associated with capturing their food normally led to periods of low food supply. The limited amount of food combined with the high-energy costs from hunting put evolutionary pressure on the genomes of early humans that placed a premium on energy. Because hunting was an effective way to obtain food as an energy source, the muscular system was preferentially supplied energy over many other energy-consuming processes within the body. This continual energy supply to muscle would maintain function of the muscular system and therefore the ability to hunt. The muscular system also responded to this evolutionary pressure from short-term food scarcity by increasing the anabolic response within muscle tissue especially when food was consumed immediately after the hunt. This enhanced anabolic response would provide the evolutionary benefit of increasing muscle size for improved function of the muscular system and a greater capacity for future hunting. Of course, this would increase the likelihood of capturing food for energy, which improved the chance of survival and the ability to pass these muscle-enhancing genes on to the next generation. Seeing that evolution occurs at a very slow rate, modern humans have not changed very much genetically relative to early humans. Consequently, just like early humans, modern human genomes also preferentially supply energy to muscle tissue during periodic food shortages while also improving the anabolic response to feeding.

      Altogether, this unique evolutionary viewpoint claims that the periodic reduction in caloric intake followed by feeding triggers an evolutionarily conserved mechanism that drives greater muscle function and hypertrophy. As a result, modern humans should be able to exploit this nutritional approach, known as intermittent fasting, to heighten muscle size and strength. Interestingly, the consumption of roughly 600 calories per day for two or three days per week followed by normal caloric intake during intermittent fasting has gained in popularity likely because it mimics the aforementioned cycling of caloric consumption. Furthermore, several lines of evidence have recently indicated that intermittent fasting triggers weight loss while also improving muscle size and performance2,3 reinforcing the use of this novel weight-loss approach as a way to also gain muscle mass and power.

 Intermittent Fasting Triggers AMPK-driven Energy Production Within Muscle

      The primary energy-regulating molecule in the body, AMPK, is also the prototypical example of a gene that has been heavily influenced by evolutionary pressure to increase the energy supply within muscle for enhanced function when whole-body energy levels are cyclically low. Again, while it may seem counterproductive to supply energy to muscle tissue when overall energy is low, from an evolutionary perspective it makes perfect sense as muscle tissue enabled early humans the ability to acquire food.

      Studies have shown that intermittent fasting activates AMPK,4 which then manages to directly increase muscle cell energy by activating energy producing processes such as glycolysis and fatty acid oxidation, which supply the muscle with energy. In addition, in response to low energy, AMPK stimulates the translocation of glucose transporters to the muscle-cell membrane, which increases the influx of glucose into the muscle cell where it is converted into energy to sustain muscular function.

 Accentuate the Muscle-building Response to Insulin

      As previously mentioned, intermittent fasting is an effective way to burn body fat. However, another advantage of intermittent fasting, not usually associated with caloric restriction, is improved muscle growth. This is because intermittent fasting reduces caloric consumption for a brief time, which triggers the evolutionarily-conserved response of muscle anabolism. This muscle-enhancing response occurs, in part, because intermittent fasting, especially when combined with exercise, potently decreases intramuscular fat stores.5 The decrease of fat within muscle tissue has been shown to enhance the muscle cell’s response to the potently anabolic hormone insulin,6 which drastically increases muscle protein synthesis supporting greater muscle growth.7

 Boost Testosterone

      In addition to intermittent fasting promoting the anabolic response to insulin, intermittent fasting also indirectly regulates testosterone levels by modulating the hormone leptin.8 Leptin is a hormone secreted by fat cells that normally functions as a signal to the brain to decrease appetite especially after eating. In addition, recent studies have shown that leptin also has the ability to reduce testosterone production.9,10 In one of these studies1 it was demonstrated that rats treated with leptin had a diminished testosterone production in response to human chorionic gonadotropin (hCG). Because hCG mimics the function of the natural testosterone-stimulating substance known as luteinizing hormone (LH), this result implies that leptin inhibits the ability of LH to stimulate testosterone production.

      Individuals with greater body fat typically have greater levels of circulating leptin.11 An extremely effective way to reduce leptin, and boost testosterone, is to reduce body fat by way of intermittent fasting. This effect was clearly demonstrated in a study12 where intermittent fasting caused a rapid decrease in body fat and circulating leptin levels, which should conceivably boost the production of testosterone for a more anabolic environment that supports superior muscle growth.

 To commence intermittent fasting restrict yourself to 600 calories a day for two or three days a week (on non-consecutive days) followed by normal caloric intake.

                 For most of Michael Rudolph’s career he has been engrossed in the exercise world as either an athlete (he played college football at Hofstra University), personal trainer or as a Research Scientist (he earned a B.Sc. in Exercise Science at Hofstra University and a Ph.D. in Biochemistry and Molecular Biology from Stony Brook University). After earning his Ph.D., Michael investigated the molecular biology of exercise as a fellow at Harvard Medical School and Columbia University for over eight years. That research contributed seminally to understanding the function of the incredibly important cellular energy sensor AMPK— leading to numerous publications in peer-reviewed journals including the journal Nature. Michael is currently a scientist working at the New York Structural Biology Center doing contract work for the Department of Defense on a project involving national security.