So has anyone actually read any of Pontzer’s papers? There are two that refer to the Hadza, one from
2012, and another from
2015, both using the same source data.
The linked article says
“the evolutionary anthropologist recounts the 10-plus years he and his colleagues have spent measuring the metabolisms of people ranging from ultra-athletes to office workers”, well that’s as may be, but he hasn’t spent 10 years measuring the metabolisms of the Hadza tribe that he’s adducing as evidence that extra exercise uses no extra calories. In fact he monitored their energy consumption for just
two weeks.
This isn’t even remotely long enough to see the effect of any particular individual changing their activity levels over months & years, so he’s drawing all his conclusions from the comparison between different individuals who exhibit differing levels of activity, and then assuming that any effect must be activity related and not due to any other confounding variables. In his 2012 paper he says himself that
“It is important to note that this was not an intervention study”, so he hasn’t tried changing the activity levels of the Hadza, or the Westerners that he’s comparing them with, and yet he claims that
“over time, metabolism responds to changes in activity to keep the total energy you spend in check”.
In the 2015 paper he says that military training
has been shown to affect TEE, but then contradicts this, saying
“comparisons across diverse lifestyles and populations have often shown little or no difference in TEE despite substantial differences in habitual levels of activity”, citing a pair of references from
Dugas et al, &
Luke et al which don’t back up his claim. Dugas et al has noted that exercise level & TEE each correlate with human development index, but hasn’t looked for the relationship between exercise & TEE. Luke et al didn’t measure exercise levels at all.
Pontzer shows that fat free mass correlates with total energy consumption (TEE), but what’s that going to correlate with, over the
long term that he hasn’t studied, if not exercise level? This is likely to be causal in both directions too: more exercise builds muscle, and the muscular are going to be more motivated to exercise. He also notes that studies of Bolivian, Gambian, and Nigerian farmers showed that energy consumption
does correlate with exercise, and cites studies from Ravussin and Westerterp which find effects of exercise on TEE too.
In 2015 he says
“we lack sufficient statistical power to rule out small or moderate effects of…physical activity on daily energy requirements”
In
2019 Thurber et al published a paper showing that a sufficient level of exercise can increase metabolic rate to the point where it exceeds the gut’s ability to digest food, and that this creates an absolute limit to the long term level of exercise that anyone can sustain. Not muscle or heart & lung fitness, but digestive system capacity. Interestingly, Pontzer is a co-author of this paper, so he seems to be riding two horses at once here.
