Debunking the Hunter-Gatherer Workout: ALR's Response

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Great response. Shame on the NYTimes for not accepting it!

Hi Jim
Thanks for the email, and I enjoyed the blog piece. To respond to your three points: first, it's true that the Hadza are smaller, on average, than the Western sample. However 1. The Westerners of similar size expended the same number of calories each day (see our Fig 1) and 2. There was no effect of lifestyle after controlling for body size across groups. Your suggestion that we simply analyze TEE/mass is intuitively appealing but misleading. We've known since the 1930's that energy expenditure increases with body size in a power- law manner, typically as Energy/time = k Mass^0.75. This is Kleibers Law, which I'm sure you're familiar with. A consequence of this is that smaller organisms (and smaller individuals within a species) will always tend to have higher ratios of TEE/mass. This is expected, and is evident within the Western sample as well. The higher TEE/mass ratio in the Hadza is exactly what we expect, and in fact what we see, in any human sample. They fit the Western pattern. As a side note, given the well known scaling of TEE with mass^0.75, I'm always surprised that many human energetics studies focus on TEE/mass when that ratio has a known relationship with mass.

Your explanation of greater TEE in Westerners as a consequence of greater fat mass is also rejected by our results. We included fat mass in our analyses, and still found no difference in TEE between Hadza and Westerners.

Second, while we didn't measure calorie intake (but see our supplementary Fig S2) we take the view that weight gain must ultimately stem from energy imbalance, with intake > expenditure. If expenditures are the same, then differences in weight are most likely due to differences in intake.

Third, for the record, the NY Times approached us and asked for a column. We agreed to summarize the work, including our interpretation. I note that in both the NY Times piece and in the PLoS paper we state that exercise is still very important for health. We feel we were honest with respect to the data.

Finally I'd note that a fair read of the available literature on energy expenditure and weight (some of which is cited in the PLoS paper) shows very little evidence that greater expenditure is protective against obesity. We are not the first to look at the data and conclude that diet plays a larger role than exercise in obesity. There is a large and growing body of literature showing that diet has a much larger effect on weight loss than exercise in intervention studies, and that TEE is remarkably similar across very different lifestyles.

Again, thanks for your interest in the study. All best,

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