It is a widely held belief that calorie restriction is necessary in order to lose weight. To question this assumption often leads to derision from those who ascribe to such a ‘fact’. However, the scientific evidence supporting the role of calorie restriction in the weight loss process is neither comprehensive nor compelling. Many studies that investigate the role of diet in weight loss confound their results by changing both energy intakes and diet quality. For example, in a recent study1, researchers investigated the effects of energy restrictions and improvements in diet on obese and overweight individuals. Subject with a body mass index of over 25 were given dietary improvements that included increased fibre and lower glycaemic index carbohydrates during 6 months of calorie restriction. Intakes of carbohydrate, protein and fat were 48 %, 28 % and 25 %. In addition, the subjects were encouraged to increase their physical activity levels, and advice was given to the subjects about lifestyle changes in regular meetings.
The results of the study showed that those subjects undergoing the lifestyle changes lost an average of 8 kg, which compares favourably to the 0.9 kg gain in weight in the control group. However, there is no way of knowing if this weight loss was fat or lean mass as this was not measured. Those subjects who participated in the 6 month trial were encouraged to sign up for a 6 to 12 month maintenance phase that was identical to the original study except that meetings for advice were given less frequently. The weight maintenance phase produce only a small 0.5 kg weight loss compared to a 0.7 kg increase in body weight in the control group, suggesting that the rate of weight loss was rapidly attenuating as the study continued. Also there were no improvements in any cardiometabolic parameters in treatment compared to control subjects (including total plasma cholesterol, plasma glucose, systolic blood pressure or diastolic blood pressure). The dropout rate of the initial phase was 11 % and only 48 % of completers enrolled in the maintenance phase.
While the results from studies such as this are often interpreted as evidence for energy restrictive causing weight loss, it is infact not possible to make such statements from the data presented. Without a control group engaged in diet improvements without energy restriction the cause of the weight loss cannot be ascribed. However, some studies have reported weight loss with low carbohydrate diets (here) and traditional diets such as the Mediterranean diet (here) without the need for energy restriction. This lends evidence to the viewpoint that when energy restriction and dietary improvements are made, it is the dietary improvements that are the cause of the weight loss. The offshoot of this is that many individuals who attempt to lose weight by both energy restriction and dietary improvements are needlessly suffering hunger for no net gain. In fact, energy restriction is possibly detrimental because over the long term it will influence appetite such that controlling hunger may become problematic. In this respect such diets may encourage weight regain.
The use of multicomponent interventions are both interesting and problematic. They are interesting because health improvements require both nutrition and lifestyle improvements and in this regard they more accurately mirror the real-world behaviours of individuals. However, at the same time, they are problematic because the cause of any changes can never be ascribed. Care is required when interpreting such studies, because authors often interpret the data in a way that is not scientifically rigorous. The inclusion of increased physical activity in such multicomponent studies is also problematic because when weight loss is seen, it is often assumed that exercise was a partial cause. However, the long term weight loss effects of low intensity exercise and increased lifestyle activities (like walking and taking the stairs) are not good. The fact that improvements in diet quality, without the need for energy restriction or exercise, are is able to cause weight loss suggests that multicomponent studies need careful interpretation.
In fact, closer inspection of the results from this study support the contention that the weight loss seen in the initial 6 month period may have comprised mainly skeletal muscle. However, the body composition was not assessed and therefore this is evidence based guess work. The pattern of weight loss, an initial rapid reduction followed by stagnation in the proceeding 6 months, is reminiscent of many such energy restriction studies that have been performed. With energy restriction, the initial weight loss is often skeletal muscle, and as lean tissue is catabolised, the resting metabolic rate of the individual falls. As this condition proceeds, adjustments to energy expenditure are made by the hypothalamus, such that after 6 months energy efficiency is improved and weight loss ceases. This is problematic because the reduced metabolic rate leaves the individuals at risk of weight regain when energy restriction is ended. In addition, the energy efficiency includes appetite that increase the risk of weight regain from hyperphagia.
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