I spent 7 weeks in Africa and I think I've found out why they're so fit.
The only reason the Kenyans are so good is because they have what we don't, the sun! The sun is what gives energy to life. If we had no sun nothing would move. That's why billions of animals flock to Alaska in the summer to feast on all the plankton created by the sun. That's why a humpback whale can eat 1.5 million calories a day in the summer (thanks to the sun) but has to nearly starve in the winter.
Life does not move in winter, all the trees are conversing energy. When spring comes shit starts getting real because of the energy from the sun.
You're only as strong as your weakest link and without Vitamin D and who knows what else the sun gives we can't perform. I had the most sweetest, ripened fruit I've ever tasted in my life, you could feel the energy going into your body and I was recovered from runs in less than 6 hours. Back in the UK the fruit is DEAD, tasteless and my legs ache forever. The food does not have the energy from the sun.
And before anyone jumps in saying why aren't other nations like India great at running they live in tropical places well they just don't have the talent like Kenyans do, they're not athletic. UK has good talent but we live in a stupid climate for humans where we only survive instead of thrive.