I don't think so. Only 10-20% of the energy we get from food can be used for manual labour, and that's neglecting rest and sleeping periods. If what GP is sayin

I don't think so. Only 10-20% of the energy we get from food can be used for manual labour, and that's neglecting rest and sleeping periods. If what GP is saying wasn't true, hunter populations wouldn't be able to survive. This is also why reduced calorie intake is much more effective than increased activity if you want to lose weight.