Energy restriction does not cause successful long term weight loss.
Energy restriction diets do not cause successful long term weight loss. Despite this energy restriction diets are still considered the only way to cause weight loss by many people, including those in the medical establishment. While weight loss is seen during the initial period of energy restriction, this weight tends to be made up to a great extent by skeletal muscle, water and glycogen. Such reductions in fat free mass are detrimental because they cause decreases in resting metabolic rate. Obesity is perceived by the body as a situation as starvation, largely due to the leptin resistance that develops. Hypothalamic insensitivity to the normal leptin feedback signal regarding adipose mass results in restrictions to energy expenditure by the hypothalamus. Forcing the body to lose weight energy restriction is therefore perceived as a threat to survival and countermeasures to down regulate energy expenditure are put in place. These falls in energy expenditure can be measured following energy restriction diets.
For example, in one study1 researchers investigated the effects of periods of energy restriction on the energy expenditure in nine obese subjects. Subjects were monitored on 2 separate occasions before periods of energy restriction and following 10 to 16 weeks of energy restriction diets. The hypocaloric diets during the period of weight loss were between 836 and 1123 kcal per day. During the energy restriction phases the mean body weight loss was 12.6 kg, and of this 72 % was body fat. The mean loss of skeletal muscle tissue was therefore 3.5 kg during the energy restriction phases. Absolute 24 hour energy expenditure decreased during energy restriction from 2347 to 1967 kcal per day and resting metabolic rate decreased from 1736 to 1576 kcal per day. Relative to fat free mass this means that the 24 hour energy expenditure decreased from 40 to 35 kcal per kg of fat free mass per day but that resting metabolic rate did not decrease (~29 kcal per kg of fat free mass per day).
Of the absolute reductions in 24 hour energy expenditure, approximately half was accounted for by reductions in resting metabolic rate, and the rest by reductions in the thermic effect of food and the thermic effect of exercise. These results support the contention that periods of energy restriction cause countermeasures aimed at reducing energy expenditure. The hypothalamus has three options when attempting to decrease energy expenditure. It can reduce the resting metabolic rate, it can reduce the thermic effect of food and it can reduce the thermic effect of activity. In the case of the obese subjects in this study, energy expenditure from all three were reduced following a period of energy restriction. This counterregulatory decrease in energy expenditure is the main reason that energy restriction diets do not work. Another problem is that the hypothalamus also controls appetite, and it can deal with perceived threat to its energy reserves by stimulating hyperphagia. Short-term this can be resisted, but long-term this is another reason energy restriction diets fail.
