The Paleo Theory Takes a Hit

[Added later: turns out caloric restriction doesn't extend life either, at least in primates; it's just unpleasant. And if you're reading this, you are one. Don't bother telling me about rodent studies.]

As nice as it is to see people trying to unify theory with action, it's even better to compare actual data against your theory, and when the theory doesn't fit the data, you fix the theory.  (Not the other way around.)  Or at the very least, you decrease your certainty about it.

Recently, Pontzer et al published a paper in PLoSONE (and Pontzer summarized it in the NYT here) about metabolic rates in a group in Africa.  Meet the Hadza:

The Hadza live in simple grass huts in the middle of a dry East African savanna. They have no guns, vehicles, crops or livestock. Each day the women comb miles of hilly terrain, foraging for tubers, berries and other wild plant foods, often while carrying infants, firewood and water. Men set out alone most days to collect honey or hunt for game using handmade bows and poison-tipped arrows, often covering 15 to 20 miles.

Paleos par excellence! A paleo wet dream! It doesn't get better than this without a time machine. So what did the researchers find, carefully measuring metabolism using two separate isotopes?

"...average daily energy expenditure of traditional Hadza foragers was no different than that of Westerners after controlling for body size." That is to say, "We found that despite all this physical activity, the number of calories that the Hadza burned per day was indistinguishable from that of typical adults in Europe and the United States. We ran a number of statistical tests, accounting for body mass, lean body mass, age, sex and fat mass, and still found no difference in daily energy expenditure between the Hadza and their Western counterparts."

There are two aspects to controlling one's physique: exercise and diet. The paleo evangelists of the world love to tell us endurance athletes that we're bad, bad people for doing long-term cardio instead of being miserable for short bursts in gyms. It turns out that side of the equation is less important than we all thought, judging by this research (which doesn't exist in isolation - look at the references). What it does mean is that diet becomes even more important.

Evolutionary Economics takes issue with the conclusion and also refers to Razib Khan's point that metabolism has undergone differential adaptation in humans who settled different parts of the world, and ate different things. (No kidding - for one extreme example, look at the fat distribution on the now very multi-ethnic sumo wrestler corps in Japan and this cannot be disputed.) That being the case, I would also argue that different populations of humans might respond differently to varying diets and exercise regimens. There has clearly been selection in muscle proteins, that your partly-sequenced blogger has found himself and his ancestors subjected to.

But most importantly, I hope the paleo exercise people start to settle down in the preaching.