By Dan Gwartney, M.D.
There is so much confusion regarding fat loss; the public is far too diverse to encompass the conditions and goals of all with one program.
The Atkins diet started a surge in sustained low-carbohydrate dieting for weight loss in the public. [The ketogenic phase only accounts for the induction period of the Atkins plan.] However, over time, it became clear to many guys who work out that building mass long-term on a low-carbohydrate diet was more difficult; for some, it was impossible.
Year-to-year, many who followed low-carbohydrate diets chronically were experiencing strength loss and reduced muscle mass. The phenomenon has also been noted in some hardcore and heavy lifters, leading many to re-introduce a more balanced macronutrient profile. The basis for the loss of mass and strength relates to the imbalance of anabolic versus catabolic processes.
The most blatant hormonal difference is the reduction of post-prandial (after eating) insulin that normally shuts down muscle proteolysis (breakdown of muscle protein) and promotes the influx of sugar (glucose) and amino acids into sensitive tissue such as skeletal muscle.1,2 This helps maximize fat loss, but at the expense of the anabolic and anti-proteolytic protection normally conferred by insulin. Some chemically-enhanced athletes use injectable insulin as part of their anabolic pharmacopeia, so the loss is moderated or erased in this group.
Another consequence of low-carbohydrate dieting that may dramatically affect muscle mass and body composition in active men is the impact on the balance between testosterone production and response versus the catabolic effects of the steroid hormone cortisol.3, 4 Most guys who work out are aware of testosterone’s role in building muscle, inhibiting fat gain, and instilling a competitive/aggressive mindset. Cortisol’s roles are nearly the opposite, promoting muscle loss, fat gain, and possibly depression.5
Human physiology developed over generations, adapting to drought, famine, war, etc. The prevalence of cultural obesity and sedentary lifestyles are very recent phenomena in mankind’s history. In times of limited food stores (measured physiologically by dietary carbohydrates and stored body fat, possibly muscle protein to a much lesser degree), the body inhibits anabolic processes and ramps up catabolic processes. This is done to reduce the metabolic demand of active, calorie-burning tissue (e.g., muscle) and release-stored nutrients, including amino acids.
The breakdown of stored fat and sugar takes place regularly between meals to provide calories to all the cells of the body. If catabolism becomes too severe or persists overlong, the body suffers structural and functional damage. So effective is the body at cannibalizing its own muscle, organs, and fat that prisoners and activists have survived over two months without eating during passive protests.6