Quick – how many people do you know who are too heavy? And how many do you know who aren’t? Chances are, you know more overweight people than thin ones, since normal weight people are now in the minority – two-thirds of US adults are either overweight or obese. How we got this way has been endlessly discussed – we eat too much of the wrong foods, we eat all the time and we don’t exercise enough. So given what we eat and how little we move, the real question is “why isn’t everyone fat?”.
Humans are designed to stockpile calories. We’re genetically programmed – just like our ancient hunter-gatherer ancestors were – to hang on to every calorie we can. These thrifty genes can work against us by helping us to store more – and the wide availability of cheap, tasty food just makes it even easier to do so. But there’s a bit of genetic programming that determines how much energy we spend every day, too – even influencing how much we move when we’re not exercising.