In 2015 a six-year study of the contestants on the Biggest Loser concluded with a shocking result. Thirteen of fourteen contestants had gained all or more of the weight back. How did it happen? Their bodies had slowed their metabolisms—in one case by a whopping 800 calories.1 In a similar vein, Scientific American reported in 2017 on several studies showing that highly active peoples, such as those in hunter-gatherer societies, do not burn more calories than their less active, western counterparts.2 Whether you cut calories or increase your activity, it seems the body finds a way to push back. That might sound discouraging but take heart, it happens for good reason.
Man Or Beast, You Burn What You Burn
The hunter-gatherer story is particularly noteworthy because it highlights a less-spoken of aspect of metabolism. It is already fairly well known that eating too few calories can lead to a metabolic slowdown. However, the idea that your body might slow its metabolism in response to high levels of activity is almost never talked about. As it happens though, this is not new information. As Scientific American notes, researchers have been collecting data on energy expenditure since the 1980s and showing that, contrary to popular belief, high activity does not lead to higher metabolisms. Whether you live on a farm or in the city, in the western world or some other seemingly more rugged environment, your average daily caloric expenditure does not drastically change. It holds for other animals as well. Monkeys and apes burn roughly the same number of calories whether they live in zoos, laboratories, or the wild. So do pandas, kangaroos, and sheep. It just doesn’t seem to matter where you live or what you do—bodies have parameters, and they work to stay within them.3
We Are What We Are, And Thankfully So
There is an important challenge to our beliefs in this. When it comes to the gym, the predominant thought process is that results come in proportion to effort. The harder we exercise, the more results we will get. By extension, we are essentially learning to believe that we can transform our bodies into whatever we want, which in turn implies that whatever we are is by default our doing. The evidence suggests otherwise. It seems that a more fair statement would be that the body knows where it wants to be and is very good at staying there.
While this might sound discouraging, there is an important upside. Without a robust system for keeping things under control, our bodies would be constantly stressed. If we had to respond to every change in our activity level by eating more or less, the business of staying alive would be much more complicated. You’d be spending all your time trying to anticipate what you need to eat if the elevator happens to go out in your building, or the bus doesn’t arrive, or you feel like playing a game of pick-up basketball. Our body’s resiliency, in short, makes daily living much less complicated. That’s a good thing.
This is not to say that we have no agency over our physical condition. The benefits of exercise and quality nutrition are many and well-documented. If you eat well and stay active you will move better, be stronger, and quite probably live longer. You might also be able to make some changes in your body fat percentage and your muscle mass. It definitely does happen. The key is to recognize that your body has as much say in how much it changes as you do, and that’s not bad.