TEXT ON SCREEN: DOES EXERCISE MAKE YOU THINNER?

HERMAN PONTZER: The traditional view is that the more active you are day to day, the more calories you’re going to spend.

TEXT ON SCREEN: ANTHROPOLOGIST HERMAN PONTZER STUMBLED ON A DIFFERENT ANSWER WHEN HE WENT TO TANZANIA TO STUDY  THE HADZA TRIBE.

HE MEASURED HOW MANY CALORIES THE HADZA BURN EACH DAY.

HERMAN PONTZER: Hunting and gathering populations are a lot more active than we are in the West. And we expected to find that the Hadza would burn a lot more calories than people in Western societies do. But, we found absolutely no difference in calories per day. That was a real surprise, and it got us thinking that maybe there’s something there that we’re not understanding.

The body spends most of its energy all day on things that we don’t see: on the immune system, reproductive system. So, what we think is going on with the Hadza is that even though they’re more active, they’re spending less energy on these unseen tasks. If you look across a global sample of populations, we see the same energy expenditures even though we know the physical activity levels are very different.

TEXT ON SCREEN: SO WHAT DOES IT ALL MEAN FOR DIET AND EXERCISE?

HERMAN PONTZER: Exercise is really important for health, but if you increase how much you exercise, over time your body will adjust to keep your energy expenditure more or less what it was before. The data show that you won’t see big weight loss just from exercise alone; that you have to also change your diet.

We think our bodies are just these simple accounting machines: calories in, calories out.  In fact, we know that they’re a lot more dynamic and complex than that.

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