Comment by dahart
3 years ago
That’s the part that’s at least slightly exaggerated, or giving a misleading impression. Exercise absolutely burns more than 0 calories, and I definitely was burning some. Calorie burn from exercise is straightforward to approximately measure, and many people walking around with iWatches and FitBits and heart monitors are doing so. What’s well known to many people is that exercise burns far fewer calories than you wish it did, and less than it feels like. ;) The article points out that aerobic exercise adjusts your RMR and it becomes more efficient over time. However, it does not become 100% efficient, even though the article seems to suggest it and doesn’t bother with any fine print. It doesn’t bother to differentiate between running and weight lifting either, and we adjust to those differently.
I would really like to see raw data because it feels like the story being told can’t possibly be complete.
This in particular feels really hand wavy: “After weeks of training, they barely burned more energy per day when they were running 40 kilometers per week than before they started to train.”
What does “barely” mean? 40km/week isn’t that much in terms of calorie burn. The 100 calories/mile rule of thumb says this would imply ~350 calories/day. And this article says a woman would have a daily calorie expenditure of 2400 already (seems high, though). So this is only 15%. But anyway, this drops after adaptation seemingly, so does “barely more” mean 50 calories/day? Or does it mean 300? Because those are very different. And to where is the difference attributable? Because someone going from sedentary to trained runner is going to get a lot more efficient at running. “Less energy on inflammation” is really hard to swallow as the primary source of adaptation, especially when this is presented as conjecture.
It does seem like the article is exaggerating. ;) This could be more about the author presenting a narrative than Pontzer’s data. Bringing in the sports physiologist to argue for the idea of exercise without countering the caloric claims adds a little perhaps predictable dramatic flair.
At some point, there’s just physics. Running a mile isn’t free, benching 100kg isn’t free. These things take work and we can calculate the minimum energy requirement that adaptation can’t escape. Our bodies do not adapt so far that exercise becomes pointless, it only shifts the balance a little (which might be enough to be demotivating for some people, but it’s still relatively minor.) I was under the impression that the total range of metabolic adaptivity for a given person might be on the order of 25%-30% maybe. That might be an over-estimate. I googled a little and found this paper mentioning adaptations of like 8%-15% for severe calorie restriction diets (depending on how RMR is measured).
https://academic.oup.com/fampra/article/16/2/196/480196
40km/wk is only 3.4 miles/day. It's only a half hour of moderate exercise a day. It sounds like the study didn't actually measure a significant exercise workload.
It was measuring women who were sedentary and trained for half marathons. For someone who was previously sedentary, 3.4 miles/day is an enormous amount of exercise. It’s certainly far more than the average American gets.
It’s not that much in terms of calories. It is a lot of physical activity for a modern human in a developed nation.
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