I remember reading the Hazada paradox, where they found these Hadza tribe members who live an active life, walking miles, hunting, and doing all physical labour, have the same maintenance calories as a Western person.

So where does the energy burn in a sedentary population come from vs highly active Hadza tribe members?

Pontzer’s research showed that while the Hadza were highly active, they actually demonstrated lower baselines of certain markers of metabolic and physiological stress over time compared to Western populations.

Don't quote me on this; I am paraphrasing things I remember from.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3405064/

> Nonetheless, average daily energy expenditure of traditional Hadza foragers was no different than that of Westerners after controlling for body size. The metabolic cost of walking (kcal kg−1 m−1) and resting (kcal kg−1 s−1) were also similar among Hadza and Western groups. The similarity in metabolic rates across a broad range of cultures challenges current models of obesity suggesting that Western lifestyles lead to decreased energy expenditure.

> So where does the energy burn in a sedentary population come from vs highly active Hadza tribe members?

P.S.: One theory I've seen is that the extra sedentary-spend is in the immune-system, which may have both beneficial and harmful effects, depending on whether it's doing useful work versus causing problems.