biophysicist Nick Lane offers a possible explanation for this in his book power sex and suicide.

https://www.amazon.com/Power-Sex-Suicide-Nick-Lane-audiobook/dp/B07P75DS9B/

Briefly paraphrased, he says that people with African ancestry have metabolisms which focus on converting energy to muscle power rather than warmth, because the climate in Africa is so hot that using energy to keep you warm is unnecessary. Conversely, people whose ancestors come from cold climates are going to have metabolisms that burn up energy to keep themselves warm. Consequently, it will be easier for people of European ancestry to burn off calories than it is for people of African ancestry. This is a speculation, but it is a speculation based on recently discovered scientific facts.