We know very well that when you made those promises to yourself about a "new year and a new you" you were deadly serious. Making a healthy eating plan and sticking to it really will show results to make you proud — but why is it so hard to stand firm in the face of all those winter goodies? It may not be down to your lack of willpower, after all. According to a new British study, evolution has very generously given us an innate subconscious urge to overeat as well as a limited ability to avoid becoming obese, especially in winter.
Though nature has given us the craving, it hasn't yet thought to develop an evolutionary mechanism to help fight the lure of sweet, fatty and unhealthy food and so prevent us from becoming overweight. Though this may seem desperately unfair, it makes a lot of sense for us, evolutionarily speaking. In our past, being overweight didn't pose as great a threat to our survival as the dangers of being underweight. And when lack of food and the cold of winter are your two biggest worries, it makes a lot of sense to pile on a few extra pounds. This means the urge to maintain body fat is even stronger in winter and explains both why we enjoy eating so much at Christmas and why our New Year's resolutions to lose weight usually come to naught.
Researchers at the University of Exeter in England have used computer modeling to predict how much fat animals should store. They began by assuming that natural selection gives animals — and that includes humans — a perfect strategy for keeping to their optimum healthy weight. The model they designed predicts how the amount of food naturally available and the perceived risk of being killed by a predator when foraging is reflected in the amount of fat stored by the animal.
The team found that, according to calculations, the animal should have a certain "target body weight" above which it tends to lose weight and below which it tries to gain weight. This predicted natural equilibrium sounds rather promising until you realize that the computer simulations also showed there is usually only a small negative effect of energy stores that exceed the optimal level. In other words, in the wild, an extra bit of weight doesn't really do that much harm to an animal that keeps healthy and is regularly active. So any subconscious "control" we may have against becoming overweight won't be as strong an urge as that arising from the immediate rewards of tasty food.
The research, "Fatness and fitness: Exposing the logic of evolutionary explanations for obesity," is published in the journal Proceedings of the Royal Society B and was written with John McNamara and Alasdair Houston from the University of Bristol. The scientific debate over the evolutionary reasons for obesity has been around for a long time. In 1962, geneticist James V. Neel proposed the "thrifty gene hypothesis," which argued that this tendency to store fat could mean a survival advantage and so may have been passed on genetically.
The study's lead author, Dr. Andrew Higginson, from the College of Life and Environmental Sciences at Exeter, says: "You would expect evolution to have given us the ability to realize when we have eaten enough, but instead we show little control when faced with artificial food. Because modern food today has so much sugar and flavor, the urge humans have to eat it is greater than any weak evolutionary mechanism which would tell us not to."
Despite all this glum news, there is perhaps a crumb of consolation. If you're feeling the pressure to stick to those well-intentioned new year resolutions, Higginson has some encouraging insight: "The model also predicts animals should gain weight when food is harder to find. 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."
You really are serious about those new year promises and you will truly thank yourself when you achieve the new you — but, if you do slip a little here and there on the road ahead, don't lose heart. You're still winning a battle that's a million years old.