I recommend reading Burn by Herman Pontzer. He explains how metabolism works and how humans have constrained energy expenditure, meaning that you only burn so many calories a day no matter what you do. For example his research show that the Hadza tribe who are very active use the same amount of energy as North Americans.
https://gsas.harvard.edu/news/colloquy-podcast-why-exercising-more-may-not-help-you-lose-weight
'We tend to focus a lot on the energy that we spend on physical activity, especially on exercise. Right? Because we're really aware of that. Our heart rate goes up, and the calories we're burning per minute or per hour are much higher when we're exercising, of course, because we can feel that. And so, we focus on activity when we think about the expenditure. But actually, even if for someone in the Hadza community, most of the calories burned every day are burned on other stuff. They're burned on immune system and on just the basic processes of homeostasis, keeping your cells alive, reproductive system, nervous system.
All of these systems that we aren't even really aware of are actually where you spend the bulk of your calories. And so, what we think is happening is the Hadza and other really physically active populations, they're spending a bit less on those other processes to sort of make room for the physical activity. So, there's no magic here. The laws of physics remain intact, undefeated. [CHUCKLING] It's just that the way that they're spending their energy is different on other tasks.
So, is that good news or bad news for their long-term health?Well, I think good news. One thing we've been looking into more recently is sort of trying to bring these results home and see what they mean here in the US. When people are more physically active here in the US, we see the same kind of compensation happening. Maybe not as severe as with the Hadza, but we see people, they start a new exercise program, they're not burning as many calories as you'd expect based on the number of calories that were assigned to them in the exercise program. So, we see the same kind of compensation happening here, too.
And what we know is that exercise is really good for us. And one of the reasons it's so good for us is that it does things like lowers our inflammation levels. It lowers our stress reactivity. It gets reproductive hormones in a sort of more healthy range, not the sort of sky-high testosterone and estrogen levels that you can see in sedentary people. And so, those compensations that we see here in the US and we see parts of that as well when we look at other communities, it hasn't been studied as well elsewhere, we think are part of the health benefits of all that activity.
So, when we look at the Hadza, they don't get heart disease. They don't get Type 2 diabetes. They don't have the kind of levels of reproductive cancers, for example, that we see in the US. These other traditional societies, them and other traditional groups, are really healthy that way. And I think that that energy compensation, that sort of re-juggling of the energy budget, is one of the big reasons that they're so healthy compared to us for those non-communicable diseases'