Many people believe that weight loss is only possible through a combination of physical activity and a reduction in the amount of calories consumed. This is based on the belief that causing an apparent energy deficit will cause the body to relinquish its stores of fat. However, evidence in the nutritional literature dating back decades shows that the obese state is akin to starvation, and calorie restriction under such conditions simply results in skeletal muscle loss, a reduction in the metabolic rate and deterioration of health over the long term. This series of detrimental changes occurs because the hypothalamus has a number of ways of increasing energy efficiency and thus preventing weight loss in the face of a perceived starvation state that results in turn from leptin resistance in the hypothalamus. One way that the hypothalamus causes an increase in energy efficiency is through the curtailment of physical activity. By controlling motivation and the provision of energy substrates, the hypothalamus can induce lethargy in the individual which is often assumed to be laziness.
That an energy reduction in the presence of the starvation state causes a reduction in physical output is well evidenced in the scientific literature in animal studies. Observation also shows us that humans in a states of starvation also lose the ability of perform intense physical activity. As obesity is akin to a starvation state it is not surprising that evidence also exists in the nutritional literature for this phenomenon. For example, in one study1<\sup>, researchers investigated the effects of energy restriction on physical activity levels during a low calorie diet and then during a period of weight maintenance where the energy intake was increased. The body weight of the subjects decreased during the period of low energy intake, but this was accompanied by a reduction in the resting metabolic rate (RMR) and sleeping metabolic rate (SMR), suggesting that counterregulatory mechanisms had been initiated by the hypothalamus. In particular the decrease in RMR may have resulted from a reduction in skeletal muscle and a reduction in the synthesis and availability of thyroid hormones.
The levels of physical activity performed by the subjects were monitored and it was reported that physical activity declined with calorie restriction. This is inline with the theory that counterregulatory mechanisms are initiated by the central nervous system during periods of energy restrictive stress. The authors inferred from both the title and abstract of the paper that physical activity levels recovered following the weight maintenance phase of the study, but this was a disingenuous use of language because while they did recover to the levels seen at the end of the diet period, the levels of physical activity were still below baseline levels following refeeding. Therefore we can conclude from this data that energy restriction causes a reduction in physical activity, and this reduction in physical activity remains following refeeding. In addition it is amazing that in the 21st century the authors did not measure the body fat levels of the subjects but instead relied on body weight. The cynical amongst us will conclude this was because the loss of lean tissue during the low calorie phase would likely be permanent and not fit with the beliefs of the authors.
Dr Robert Barrington’s Nutritional Advice: Low calorie diets do not work folks. If you are overweight and want to lose weight, the surest way to fail over the long term is to restrict your energy intake and perform physical activity. If this route is taken, initially weight loss will occur. However, this weight loss will be comprised of a significant amount of lean body tissue, including skeletal muscle. At the same time counter regulatory mechanisms will be initiated that will detrimentally and semi-permanently damage metabolic regulation, energy utilisation and hormonal balance. Eating a high quality diet devoid of the metabolic poisons that cause weight gain, and ensuring adequate intakes of fibre and essential nutrients, in combination with resistance training is the way to ensure improvements in body composition.
RdB
