Weight gain and obesity has traditionally been viewed as being caused by a positive energy balance that results from too high an energy intake in combination with too low an energy expenditure. However, advances within the last 2 decades are starting to provide evidence that challenges this assumption. One line of evidence that challenges the hypothesis that comes from the failure of forced physical activity to cause successful long term reversal of obesity subjects. Another line of evidence comes from the inability of forced very low calorie diets to produce significant weight reduction when compared to diets of higher calorie intake. This second point is pivotal, because if the degree of restriction of calories is not related to the amount of weight lost, then the hypothesis that the degree of calories is related to weight gain also becomes false.
For example, researchers1 have investigated the effects of 3 very low calorie diets on weight loss in 76 obese women. The diets were liquid formula that contained either 420, 660 or 800kcal, and vitamins and minerals at the current (1992) recommended daily amount. The subjects were randomly allocated to receive one of the diets for 6 months and also received group instruction on behavioural and dietary methods of weight control. The results showed that subjects consuming the diets lost an average of 17.8kg in 6 months. However, there was no significant difference between the weight loss of the 3 groups. Weight loss was 18.2, 18.5 and 16.6kg for the 420, 660 or 800kcal diets, respectively. There was no significant difference between the loss of fat free mass experienced between the subjects which at the end of the trial was 3.1kg.
These results suggest that severe calorie restriction does not cause weight loss over and beyond slightly less extreme energy intakes. Of interest, those consuming the most calories actually lost the most body fat over the 6 month trial. Subjects on the lowest calorie diet reported decreased levels of hunger, which suggests that they had significant ketone body production contributing to their energy needs, which is supported by this group having the highest serum acetone concentrations at week 9. Interestingly, all of the low calorie diets cause an increase in the reported cases of constipation, dry skin, dizziness, cold intolerance and hair loss. This suggests that these sort of diets are not beneficial to the health if followed long term. This study suggests that there is no advantage to very low calorie diets in terms of weight loss, which supports the findings from other studies in this regard.
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