The cover story in February's issue of Scientific American is titled "Workouts and Weight loss. Learn the surprising evolutionary reason why exercise alone won't shed pounds - and what to do about it." (1) The evolutionary reason might be surprising but for readers of my column, that exercise, alone or otherwise for that matter, does not help you lose weight is not a new news flash. "What to do about it" is a teaser to make you want to buy this issue of Scientific American and find out how to lose weight.
Herman Pontzer, the author of this review of his important work in energy expenditure in humans and in the great apes, is an anthropologist at Hunter College. He studies how many calories a body burns in a day by the doubly labeled water method, a straightforward, completely safe and accurate gold standard for measuring this. It requires the subjects to drink every drop of an incredibly expensive bottle of water enriched with two rare isotopes, deuterium and oxygen 18.
One group he has studied this way are the Hadza of Tanzania, an ethnic group of less than 1000 individuals who live by hunting and gathering the way humans have for a long time. In one treck described in this article, Professor Pontzer followed some Hadza men who had shot a giraffe with a poisoned arrow and had to track him for miles until he died and they found him and butchered him and carried the meat back home. That day they couldn't find the giraffe so they had to come home empty handed and eat what the women had gathered of roots and berries. What Pontzer has found that confirms long standing data in other groups, is that Hadza men ate and burned about 2600 calories a day, and Hadza women about 1,900 calories a day, the same as adults in the US and Europe who don't have to live such an arduous life style.
Besides this uncanny finding that humans burn the same number of calories whether they are Hadza, elite athletes or couch potatoes, Pontzer has found that humans use a lot more calories than chimpanzees and gorillas, and also that Hadzas, lean by city human standards, carry twice as much fat as chimpanzees who are sitting around in zoos.
He concludes that, "All the evidence points toward obesity being a disease of gluttony rather than sloth...the primary culprit in the modern obesity pandemic must be the calories consumed."
The assumption that since the problem of obesity is not on the side of the equation that you are studying it must be on the other, is not necessarily correct. Eating and obesity is just as anomalous and the classic calorie accounting is just as wrong and mysterious. Also "gluttony" is a little harsh.
1. Pontzer H. The exercise paradox. Scientific American. February 2017; 316:26-31.