Extra weight gain through yo-yo dieting

‘Tis the season to be jolly and as the festive period gets well under way, many people will be consuming larger amounts of food and alcohol over the coming weeks. As a result, they’re probably already considering the almost-mandatory January detox and diet regime, possibly even being the New Year’s resolution for 2017. In fact, losing weight and staying fit and healthy are consistently the top two New Year’s resolutions as reported by US firm Nielson.

However, researchers from the universities of Exeter and Bristol, as part of the EU-funded EVOMECH (The evolution of mechanisms that control behaviour) project have warned against one particular type of intense dieting that they argue can actually cause additional weight gain. They found in a study recently published in the journal ‘Evolution, Medicine and Public Health’ that people who engage in ‘yo-yo’ dieting – a vicious cycle of weight gain and evermore severe dieting to combat such weight gain – triggers a survival mechanism hard-wired by evolution that causes the brain to interpret repeated diets as periods of food scarcity. As a result, when a person is not actively dieting, the brain urges the body to eat more and store more fat.

They explain that animals respond to the risk of food shortage by gaining weight, which is why garden birds, including the very seasonal red robin, are much plumper in the winter, when seeds and insects are much harder to find.

The scientists constructed a mathematical model to investigate the phenomenon in a simulated animal that does not know when to expect its next meal. It showed that during times of scarcity, an animal that grabs the opportunity to put on weight has the best chance of passing on its genes.

Consequently, the researchers’ model when applied to humans, who evolved in environments where reliable food sources were both sometimes plentiful and sometimes scarce, predicts that the urge to eat increases hugely as a diet goes on. Importantly, in an age where increasing obesity rates have become one of the biggest public health concerns in the West, this urge won’t diminish as weight is gained because the brain becomes more convinced that it will need to make preparations for a famine.

Dr Andrew Higginson, Senior Lecturer in psychology at the University of Exeter and one of the study authors commented: ‘Surprisingly, our model predicts that the average weight gain for dieters will actually be greater than those who never diet. This happens because non-dieters learn that the food supply is reliable so there is less need for the insurance of fat stores.’

‘Our simple model shows that weight gain does not mean that people''s physiology is malfunctioning or that they are being overwhelmed by unnaturally sweet tastes,’ added Professor John McNamara, of the University of Bristol''s School of Mathematics. ‘The brain could be functioning perfectly, but uncertainty about the food supply triggers the evolved response to gain weight.’

So this then begs the question, what is the optimal way to lose weight? ‘The best thing for weight loss is to take it steady. Our work suggests that eating only slightly less than you should, all the time, and doing physical exercise is much more likely to help you reach a healthy weight than going on low-calorie diets,’ Dr Higginson advises.

‘For more information, please see:
CORDIS project page’