Why New Year is the worst time to make a resolution to lose weight
Like animals, we face subconscious urges to overeat in winter, study finds. What’s more, evolution has not prepared our bodies to resist modern foods packed with sugar and flavour
Have you just started your New Year diet? New research suggests it’s the worst possible time to be trying to lose weight. That’s because we’ve evolved to have subconscious urges to overeat in winter, according to a study by the University of Exeter.
In the past, being overweight did not pose a significant threat to survival compared to the dangers of being underweight, the researchers say. The urge to maintain body fat is even stronger in winter when food in the natural world is scarce. We therefore don’t have – yet – an evolutionary mechanism to help us overcome the lure of sweet, fatty and unhealthy food and avoid becoming overweight. This explains why we enjoy eating so much at Christmas, and our New Year’s resolutions to lose weight usually fail.
“All animals, including humans, should show seasonal effects on the urge to gain weight. Storing fat is an insurance against the risk of failing to find food, which for pre-industrial humans was most likely in winter. This suggests that New Year’s Day is the worst possible time to start a new diet,” says lead author Dr Andrew Higginson, from the university’s College of Life and Environmental Sciences.
Higginson and his team arrived at this conclusion by using computer modelling to predict how much fat animals should store. They assumed that natural selection gives animals, including humans, a perfect strategy to maintain the healthiest weight. Their model predicts how the amount of fat an animal stores should vary according to food availability and the risk of being killed by a predator when foraging.
The model shows that the animal should have a target body weight above which it loses weight and below which it tries to gain weight. Simulations showed that there is usually only a small negative effect of energy stores exceeding the optimal level, so subconscious controls against becoming overweight would be weak and thus easily overcome by the immediate rewards of tasty food.
“You would expect evolution to have given us the ability to realise when we have eaten enough, but instead we show little control when faced with artificial food,” says Higginson. “Because modern food today has so much sugar and flavour, the urge humans have to eat it is greater than any weak evolutionary mechanism which would tell us not to.”
The study, “Fatness and fitness: Exposing the logic of evolutionary explanations for obesity”, is published in the journal Proceedings of the Royal Society B.