I would like to better understand the relationship between exercise and TDEE. If I understood correctly, you mentioned a couple of times here and there that chronic exercise does not increase TDEE, and there are some other sources stating that while there are many benefits to exercising, losing weight may not be one of them (like Herman Pontzer in his book about misunderstood science of metabolism).
This seems counter-intuitive to me. From a layman’s perspective, the muscles would need energy to perform work, so more work sounds like more energy needed, in addition to the BMR which the body needs to stay alive. And after all, TDEE calculators still seem to factor in how active or sedentiary you are.
Could you please expand on this a bit more? I.e., why would exercise not increase TDEE?
It is not an all-or-none dichotomy, but there is complex adaptive physiology at play. Unfortunately our intuitions on such things tend to lead us to erroneous conclusions.
Also note that we are not saying that exercise does not play a role in weight loss, as it most certainly does; rather, the mechanism by which it can facilitate weight loss has less to do with directly “burning calories”, and more with things like appetite regulation (which impacts calorie intake) and influencing other metabolic functions.
Thank you Austin, so it seems like it is still unclear how exactly the body compensates the calories burned through physical activity.
The study only compared two very different lifestyle groups, i.e. hunters and gatherers vs. modern sedentiary city population. I wonder whether these findings can be generalised, given that the hunters and gatherers have adapted to this lifestyle over millennia and have spent their whole lives running and hunting for the most part of the day.
Would the findings be the same if we compared a group of inactive city population with a group of city population doing vigorous strength training and conditioning for e.g. 4 times per week?
How fast does the adaptation occur that the body reduces other functions of the body to compensate the extra energy expenditure caused by exercise?
Is there an amount of activity that cannot be compensated anymore by reducing energy expenditure on other functions? E.g., there have been these stories that Michael Phelps in his prime was consuming up to 8000 kcal per day. Maybe that isn’t true at all (Austin, you surely will be more familiar with competitive swimming), but the body cannot reduce the energy expenditure on other biologic functions beyond a certain amount I would assume? (e.g., if the BMR was 2000 kcal, even if all other life functions were reduced to zero, the body could only compensate 2000 kcal worth of excess physical activity to stay at the same TDEE?)
Lastly, if physical activity does ultimately not affect TDEE, do we still need separate metrics for BMR and TDEE, or would TDEE not equal BMR if the body would compensate physical activity anyways?
Sorry for all these questions, I’d just like to better understand.
The linked article provides a very limited summary/overview, but this concept / field / argument is not limited to just one study. There are other populations and contexts that have been studied, such as energy expenditure in individuals in modern settings training towards a marathon, where there is similar evidence of adaptation in energy expenditure. If you are interested in diving in further, I would either seek out the primary literature on the matter or, for a potentially more accessible source to start from, see Pontzer’s book.
Yes, of course, this is observed at the extremes of physical training.
Again: this is not a simple dichotomy of physical activity affecting vs. not affecting TDEE. It is a discussion of how the traditional “additive” model is overly simplistic and fails to explain what is actually observed in the real world (i.e., adaptation and apparent constraint on overall expenditure).