Herman Pontzer è un antropologo evoluzionista e professore presso la Duke University: ha dedicato buona parte della sua carriera allo studio delle calorie, passando oltre 10 anni a misurare in che modo queste vengono assorbite dai soggetti più disparati. Il suo ultimo libro, “Burn”, è dedicato a smantellare alcuni dei miti più diffusi intorno al metabolismo umano.

Much of his work takes him to Tanzania, where members of the Hadza tribe still get their food the way our ancestors did — by hunting and gathering. By setting out on foot each day to hunt zebra and antelope or forage for berries and tubers, without guns or electricity or domesticated animals to lighten the load, the Hadza get more physical activity each day than most Westerners get in a week.
So they must burn more calories, right? Wrong.

Secondo Pontzer, il metabolismo umano è ottimizzato intorno al concetto di accumulare massa grassa, al punto che risponde a cambiamenti nelle abitudini alimentari e di esercizio fisico, frustrando i nostri tentativi di perdere peso, quanto meno nel lungo termine.

My work with the Hadza showed that, surprisingly, even though they are so physically active, Hadza men and women burn the same number of calories each day as men and women in the U.S. and other industrialized countries. Instead of increasing the calories burned per day, the Hadza physical activity was changing the way they spend their calories — more on activity, less on other, unseen tasks in the body.

The takeaway for us here in the industrialized world is that we need to stay active to stay healthy, but we can’t count on exercise to increase our daily calorie burn. Our bodies adjust, keeping energy expenditure in a narrow range regardless of lifestyle. And that means that we need to focus on diet and the calories we consume in order to manage our weight. At the end of the day, our weight is a matter of calories eaten versus calories burned — and it’s really hard to change the calories we burn!

Tuttavia, questo non rende l’esercizio fisico inutile o trascurabile, al contrario. Gli Hadza (che in media compiono 16.000 passi al giorno) vivono fino ai 70 anni e non sviluppano malattie ampiamente diffuse nella società occidentale, come il diabete, l’obesità o le malattie cardiovascolari.

All those adjustments our bodies make responding to exercise are really important for our health! When we burn more calories on exercise, our bodies spend less energy on inflammation, stress reactivity (like cortisol), and other things that make us sick.