Many people find that they spend their lives alternating between dieting, losing weight and then gaining weight again – so-called yo-yo dieters. They will lose weight only to gain even more when they stop dieting because they will often overeat during these periods.

What the studies show

A study which was published in Evolution, Medicine and Public Health magazine and showing research by the Universities of Exeter and Bristol theorised that the reason a yo-yo diet regime leads to weight gain is because the brain interprets a shortage of food as a famine situation and so leads to the body storing fat. On the other hand non-dieters do not store extra fat because they learn that food is readily available.

The study was based on observations of animals and birds. Through evolutionary process they have evolved a system of gaining weight during times of food shortages – as shown by birds which grow fatter during winter food shortages. Humans also learned through their evolutionary development that in a world where food was either plentiful or unavailable then those who were fatter were more likely to survive. In animals the study showed that those with the best chance of survival – and therefore of furthering the species line – would be better able to do so by gaining weight to see them through food shortages.

With the worldwide rise in obesity levels scientists are searching for the reasons why people are unable to resist overeating despite the ready availability of food. The study’s findings offered the prediction that continuing to diet increases the overeating urge despite any increase in weight gain because of the brain’s instinct to store fat.

The best way to lose weight

Professor John McNamara, of the University of Bristol, pointed out that the study did not attribute weight gain to any malfunctioning of the body’s physiology or of any food-related influences, rather that uncertainty about food supply can trigger the deep-seated weight gain response.

As yo-yo dieting has been comprehensively proven not to work and fad diets can offer only short term solutions it is clear that the best and most effective way to lose weight and keep it off is to do so at a slow and steady pace according to Dr Higginson. His advice is that eating slightly less than you do normally and taking physical exercise is much more likely to lead to a healthy weight loss than a low-calorie diet can.

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