Calorie restriction is controversial with regard weight loss because research has reported that the degree of loss weight is not related to the deficit of energy experienced. Very low calorie diets should produce greater weight loss than moderate calorie diets but this is not the case (here). Using exercise to create weight loss in obese individuals is also controversial because despite some short term weight loss, the long term success rates of exercise regimens is not good. This suggests that the traditional view of obesity, that it is a result of too much food with too little physical activity, is not correct. In fact research has shown that increasing the quality of the diet without calorie restriction is as effective at causing weight loss as an exercise programme (here). There is therefore still controversy surrounding the ability of calorie restriction and exercise to cause weight loss in obese individuals.
For example, researchers1 have compared the effects of a severe energy restrictive diet (40% of maintenance calories) with a moderate energy restrictive diet (70% of maintenance calorie) in 30 obese women. Subjects followed a maintenance diet for 1 week and then followed their randomly assigned diet for 3 months. Each group of subjects was also assigned randomly to receive no exercise, aerobic exercise or aerobic exercise plus circuit training. All exercise programmes were chaperoned to ensure compliance. At baseline and 3 and 6 months the energy expenditure of the subjects was assessed by indirect calorimetry and body fat was assessed by hydrostatic weighing. All subjects lost weight throughout the study. However, the results showed that exercise had no effects on weight loss, with those receiving supervised training losing no more weight that those on dietary restriction alone.
Those subjects consuming the low energy diet lost a similar amount of body fat to those consuming the moderate energy during the first 3 months of the study. After this time the loss of body fat was greater in the lower calorie group such that over the entire study the difference was 11.7 versus 8.3kg. However, severe energy restriction cause a greater loss of fat free mass compared to moderate energy restriction (2.8kg versus 1.8kg, respectively). When comparing the whole 6 months, there was no significant difference between either diet in terms of fat loss attained. Overall severe energy restriction caused 78.3% of weight from fat whereas moderate energy restriction caused 78.4% of weight from fat. The loss of fat free mass is likely the cause of the 6.5% reduction in resting metabolic rate (RMR) seen with severe energy restriction. In comparison, the RMR declined by 1.7% with moderate energy restriction.
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