The failure rate in those that use energy restriction as a mechanism to lose body fat is high. Studies that have investigated weight loss through calorie restriction have generally reported successful initial results, but most of the subjects tend to re-gain the lost weight when the attention of the researchers, chaperones and trainers is withdrawn. Other studies investigating the effect of dietary improvement without calorie restriction in contrast have reported successful long-term weight loss. The reason that calorie restriction does not result in long-term weight loss is because it fails to take into account he cause of the weight gain, which is metabolic dysfunction and appetite deregulation caused by high intakes of nutrient poor foods that contribute to a poor quality diet. The defining characteristic of overweight individuals is insulin resistance. While high quality diets have been shown to address this underlying cause, energy restriction have not.
For example, one study1 investigated the effects of a 7 day very low calorie diet on metabolic parameters of 14 severely obese individuals. All the patients had type 2 diabetes and had a body mass index of over 40 kg/m2. The diet consisted of 400 kcal/day but no specific attention was paid to the quality of the diet, except that it satisfied the Italian Standard of Care. Following 7 days on the very low calorie diet, the subjects lost 3.22 % body weight, and off this 42.0 % was fat. In addition, fasting glucose and triglyceride levels decreased significantly. In addition, the disposition index (DI), as assessed by a hyperglycaemic clamp method, increased from 59.0 to 75.5 mL·min-1·m-2 of body surface area, suggesting that glucose disposal had improved. However, no improvement in insulin sensitivity was reported, suggesting that the improvement in glucose disposal was due to improvements in β-cell function.
These results support the large body of evidence that shows short-term weight loss with calorie restriction. The subjects lost 3.58 kg (3.33 %) of body weight in just a week, but only 42 % of that weight loss was fat. This is concerning because it suggests that lean mass might have accounted for a large proportion of the weight loss. If this was the case, then when normal eating is resumed, the decrease in lean mass would reduce resting metabolic rate, which would subsequently increase the risk of weight re-gain. By allowing a slow transition from metabolic abnormality to metabolic normality, a non-calorie restricted high quality diet does not cause this problem. The fact that insulin sensitivity was not improved with this diet also suggests that the underlying metabolic abnormality had not improved. Short-term very low calorie diets may therefore be detrimental to sustained long-term weight loss.
RdB
