Ketogenic Diets Cause Muscle Loss

Bodybuilders and image-conscious people diet to lose fat, and they exercise to tone and build muscles. Unfortunately, most dieters lose both body fat and muscle mass because of extreme caloric restriction, excessive cardio, and unwise use of stimulant-based weight loss products and thyroid hormones. The physical and emotional stress that accompanies weight loss can also disrupt sleep, which promotes fat gain and interferes with optimal hormonal balance.

Preserving muscle mass is challenging during low calorie dieting and exhaustive physical exercise. Supporting lean mass, tissue repair, and muscle growth requires adequate intake of calories, amino acids, and other macro- and micronutrients. Losing weight while maintaining muscle mass requires a careful balancing act between caloric restriction and exercise.

Every six months or so, a new diet book appears on the New York Times bestseller list. People are often drawn to a diet's novelty rather than its validity. Most diets restrict something. Calorie restriction ranges from the starvation-inducing very low-calorie diets (around 500-800 calories per day) to very slight (200 calories below maintenance) with "cheat days."

The basis for all successful weight loss programs is caloric restriction and long-term compliance, coupled with lifestyle factors such as exercise and sleep. However, calories are not calories, as followers of the Atkins Diet and similar programs have learned. Most studies show that high protein, low carbohydrate diets work best during the first 6-months of weight loss. After a year, however, almost all reduced calories diets are equally effective.

The Atkins diet severely restricts carbohydrate intake, which results in the production of ketones formed through the incomplete breakdown of fat. The Atkins diet is not a true ketogenic diet because it gradually reintroduces carbohydrates. However, the dramatic weight loss that occurs during the ketogenic phase has made the diet a lightning rod for media attention and resulted in score of copycat diets. Unfortunately, many people are unable to comply with the severe carbohydrate restrictions.

Ketogenesis refers to the creation of ketone in the liver that occurs when the body is desperate for energy due to low carbohydrate availability. The body has complex sensing mechanisms that respond to energy availability and body weight. For example, mTOR is a powerful signaling pathway that responds to changes in energy, nutrients, and growth factors. Nutrients and growth factors activate mTOR, which promotes muscle protein synthesis. Energy deprivation and ketosis suppresses the pathway. When the body is well fed and growing, mTOR is "turned on;" conversely, when energy (most strongly affected by glucose availability to the cell) is low, mTOR is "turned off." Bodybuilders are most interested in activating mTOR in muscle, as well as turning it off in fat tissue. Unfortunately, the natural signals are generally not tissue-specific, meaning that what increases muscle-building also tends to promote fat gain; the opposite is also true, to increase fat loss, one risks increasing muscle loss. This may account for some degree of the association of muscle loss during dieting. Ketogenic diets restrict carbohydrate intake to 10 to 20 grams per day.

Will following a ketogenic diet reduce muscle gains or promote muscle loss? Sadly, it appears this may be the case, particularly for drug-free bodybuilders. Ketogenic diets cause much lower blood insulin levels than normal. High levels of insulin activate the mTOR pathway and increases muscle growth. Studies in children on ketogenic diets have shown that they experience growth impairments in height and mass.

Very low-carbohydrate diets increase muscle loss in drug-free bodybuilders. The loss of anabolic/anti-catabolic signaling from reduced insulin concentrations, along with increased thyroid hormone activity (a catabolic hormone), and reduced resting testosterone levels, combine to promote muscle loss and inhibit muscle gains.

In recent professional bodybuilding shows, some athletes failed to reach former levels of competitiveness. No names will be mentioned out of respect for the efforts and frustration these men endured. Some of these athletes followed a ketogenic plan. Even for drug-enhanced bodybuilders, a ketogenic diet may produce a minor but significant deficit that can mean the difference between winning and losing.

When dieting, people seek the fastest and most effective way to lose fat. For athletes and bodybuilders, ketogenic dieting is counterproductive. Muscle loss is too high a price to pay for reduced fat.

References

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McCarthy JJ, Esser KA. Anabolic and catabolic pathways regulating skeletal muscle mass. Curr Opin Clin Nutr Metab Care, 2010 May;13(3):230-5.

McDaniel SS, Rensing NR, et al. The ketogenic diet inhibits the mammalian target of rapamycin (mTOR) pathway. Epilepsia, 2011 Mar;52(3):e7-e11.

Neal EG, Chaffe HM, et al. Growth of children on classical and medium-chain triglyceride ketogenic diets. Pediatrics, 2008 Aug;122(2):e334-40.

Weinheimer EM, Sands LP, et al. A systematic review of the separate and combined effects of energy restriction and exercise on fat-free mass in middle-aged and older adults: implications for sarcopenic obesity. Nutr Rev, 2010 Jul;68(7):375-88.

DISCUSS KETOGENIC DIETS ON THE MUSCULAR DEVELOPMENT FORUM