Governments are always telling us to eat less and exercise more to be healthier, but this presents an obvious problem. Being active is liable to make you hungrier, so there’s a risk you end up eating extra to compensate and putting on more weight than if you’d never got off the sofa in the first place.
Dieticians dream of the day when they can design diets for people where they are more active but don’t get hungry in the process. Unfortunately, it’s trickier than you might think: we’re still searching for the mechanism that governs how the energy we expend translates into our level of appetite. And as we shall see, that’s by no means the only thing that makes this area complicated.
Mysteries of Appetite
There is much that we don’t understand about the effect of increased activity. Most of us burn different amounts of calories on different days—gym-goers have days off, while everyone has days where they walk around more shops, do more housework or whatever.What could lie behind this difference? One possibility is that physiological processes change in people who do more exercise—for instance, their gut hormones might be released in different concentrations when they eat, potentially with a bearing on how much food they need.
Our Study
To examine what happens in the real-life situation, rather than the lab setting, I’ve co-authored a new study that looks at what happens to people’s calorie intake on days when they are more active without deliberately taking exercise—this could be anything from a trip to the dentist to a day out at the beach with the children. We looked at 242 individuals—114 men and 128 women. We found that their amount of activity did have a bearing on how much they ate, but that their resting metabolic rates influenced their appetites as well—in other words, overweight people tended to eat more.This is another step forward in understanding the relationship between activity and the calories we consume. But don’t expect this to translate into a magic formula for optimizing everyone’s relationship with activity and food any time soon. There are many variables that have barely been taken into account by researchers. Most work has tended to focus on white men aged 20-30, for instance, yet there is evidence that women are more prone to compensate for extra physical activity by eating.
Equally, different genetic characteristics are likely to be important—some people are more fidgety, for instance. Then there are differences in people’s psychology and to what extent they use food as a reward. People who have been losing or gaining weight will have different appetite signals to people whose weight is stable. The time of the activity in the course of the day is likely to make a difference, too.
I doubt that in my lifetime we will reach a point where we can look at any person’s entire genetic make-up and tell them exactly what will work for them. What we can say from our study is that many people are liable to eat more when they are more active. Just moving more will not lead to spontaneously losing weight—people should be aware of this and watch how much extra they eat as a result.
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