Comment by projektfu

Some of the papers have strange errors that suprise me that they passed peer review. For example, "Extreme events reveal an alimentary limit on sustained maximal human energy expenditure" by Thurber, others, and Pontzer has a figure labeled "Fig. 3 Maximal Energy Intake". First, it appears that one of the charts is labeled incorrectly. I assume it is the first one, and they swapped "Overfeeding" with "Endurance". Second, it seems that taking the disparate types of "event" and putting them together on the Energy Intake graph causes them to have a flat slope, whereas the slope would be somewhat positive for the subgroups.

This was like one of the first few things I looked at in this body of research, I wasn't combing through everything to find an error. But it's strange. Finding an error quickly is a red flag to me.

Overall the study I'm looking at is interesting. I'm not sure they adequately demonstrated the finding of a caloric intake limit of 2.5x BMR but there appears to be a definite negative correlation of duration of sustained activity and energy expenditure (or metabolic scope, a multiple of basal metabolic rate). The numbers are very tightly clustered around the trendline, which is kind of odd, given how widely the numbers vary in other graphs. So either this is a very close correlation or something is strange with the data.

Glancing through the papers in PubMed, I think that the implications in the article are way stronger than the papers support. One paper said that perhaps 25% of the calories expended in exercise are borrowed from a reduction in BMR. The article made it seem like they were completely offset. The article referenced above apparently used two very different groups (overfeeding and endurance competition), and used the first to study the limit of energy intake and the second to study the long-term limit of energy expenditure, but people are making claims about energy intake in endurance athletes. Maybe when you're working hard, the gut is able to adapt and pull in more calories. Perhaps there is a limit to how much the gut is willing to accept when there is a calorie surplus.

Maybe I'm way off base.