It is that time of year again when people make new years resolutions to lose weight. Large numbers of new gym memberships are purchased and people begin calorie restrictive diets with the best of intentions. However, the road to hell is paved with good intentions, and this strategy of combining a restricted energy intake with aerobic exercise is doomed to failure because scientifically it has been shown time and again to result in no net weight loss in the long term. In fact more recent studies into the metabolic effects of low and very low calorie diets in combination with aerobic exercise have shown that such regimens are damaging to the long term health of the individual because they cause a decrease in the amount of skeletal muscle mass and this in turn is reflected in a low resting metabolic rate. As resting metabolic rate falls due to skeletal muscle catabolism, the risk of weight regain rises dramatically. This is evidenced by the large numbers of yo yo dieters who go from one diet to another while getting fatter.
Studies have investigated the effects of energy restriction on the structure of skeletal muscle, and these studies are interesting from a weight loss perspective, because analysis of the results can give useful insights into the sorts of detrimental effects that can be expected from such diets. One such study used cadavers from autopsies to assess the effects of energy restriction on the structure of skeletal muscle1. Cadavers were split into groups based on the degree of energy restriction, ranging from no energy restriction (controls) through acute starvation to chronic starvation. Acute starvation produced no detectable changes to skeletal muscle structure in terms of protein content, muscle mass or energy contained within the muscle. Therefore very short periods of calorie restriction may not cause detrimental effects on the structure of skeletal muscle. However, as might be expected there was a considerable reduction in the amount of glycogen within the muscle tissue which was between 50 and 70 % of control values.
However, more serious structural changes were associated with chronically starved individuals. In such cases the skeletal muscle had atrophied to around 50 % of the control values, although there was a large variation between subjects. Mean values included a 53 % reduction in water, a 46 % reduction in collagen, a 65 % reduction in non-collagen proteins, a 40 % reduction in lipids, a 54 % reduction in DNA, an 82 % reduction in RNA, a 90 % reduction in glycogen and a 60 % reduction in total energy. The authors noted that 85 to 95 % of these changes could be noted by simply examining the muscles of the individuals. As muscle tissue comprises around 40 % of the total body mass, a significant weight loss can occur if skeletal muscle is sacrificed. Studies measuring the weight lost by individuals on low and very low calorie diets show that up to 50 % of all weight loss is in the form of skeletal muscle. Once this muscle has been catabolised, evidence suggests that resting metabolic rate becomes semi-permanently reduced.
Dr Robert Barrington’s Nutritional Advice: Low and very low calorie diets are detrimental to the health. While weight loss typically occurs on such diets much of that weight is in the form of skeletal muscle. High quality diets without forced calorie restriction in combination with high intensity training such as resistance training have been shown to be the best way to lose body fat while maintaining skeletal muscle mass. Weight loss may not occur in such diets as skeletal muscle mass often increases, but the loss of significant amounts of body fat produce significant body composition improvements. Leaving behind the tired mantra of weight loss and replacing it with a new paradigm based on body composition improvements is therefore a necessary first step in the pursuit of a healthier lifestyle.
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