Ever since I got a job working remotely (sleeping 8-10 hours/day and working whenever I want/feel like it) and have eaten 100% clean (reddit.com/r/mealprepsunday has helped immensely with this) I've felt like a robot. Infinite energy. Infinite clarity.
The question at the end seems the most important part of this article. What is their diet? I'm willing to bet it doesn't include soda, energy drinks, and deep-fried foods.
"The hunter-gatherers are also much healthier. Not a single one is obese, and the mean BMIs among the tribes was between 18.3 and 26.2, which is considered quite slim. They also tend to have lower blood pressure, better heart conditions and higher levels of physical fitness.
Thus comes a critical question. If we can't blame the lack of sleep as causing our obesity, mood disorders and the like could it it be that the reason we feel so unrested is because of poor health?"
The groups studied all live and are genetically from within 20 degrees latitude (S). USA is from 30--50 deg N, and genetically probably higher. I would be willing to bet that higher temperatures and longer days tend to make your sleep shorter.
