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Does Dieting Make You Fat?

In an intriguing Letter to the Editor in the British Journal of Nutrition, G. Cannon pointed out that in some scientific literature there are reports that would indicate that those who diet may lose weight in the short term, but over time they usually gain back any weight lost and often end up weighing more than they did before starting the diet regime. The long term result of dieting seems to have the opposite of the desired goal.


Most scientific studies are short in duration- often 12 months or less. Very few scientific studies follow subjects after the termination of the “experiment”, and so, during the strict confines of the experiment, weight loss is often achieved, and publicized with great fanfare. The critical post-experiment period is not reported. When subjects go back to their “normal” diet and “normal” lifestyle, gorging can occur that reverses any results of the experimental regime.

Cannon argues that this rebounding effect which is well known to any dieter, may not be ‘psychological’ but may have deeper evolutionary roots. In our hunter gatherer stage, when the next meal was not predictable, we became programmed to over eat when food was available. After a period of food deprivation (or as occurs during a diet), our bodies developed mechanisms to store calories by over-riding signals of satiety and increasing hunger signals -even when they were not necessary. Your body forces you to store calories in anticipation of the next period of food deprivation - even if it never comes.

Several examples can be used to support this hypothesis including data from domestic and laboratory animals, energy restrictions to developing foetuses and newborns, and populations subject to famine.

It would seem that the magnitude of the rebound after a period of restriction - such as occurs when one is dieting - is higher when food and drink is available ad libitum (without restrictions), when the foods available are calorie dense, and when energy expenditure is low due to low physical activity. Taking these observations to heart may help dieters explain their lack of success at keeping weight off over long periods of time after dieting. It may also provide them with a strategy to succeed in their goal to permanently lose weight.


Dieting. Makes you fat? Brit. J. Nutr. 93: 569-570.

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