It sill blows my mind how little we know about our body. We are aiming to sent someone to Mars, but we can't figure out what to eat. It seems the best default is to try to simulate what we've been eating for a past 50000 years and modify accordingly. When I first tried slow carb diet I lost 5kg in 3 weeks and my general well being improved. I tried it again, but the effect wasn't that strong.
It is unfortunate that very few researchers study nutrition as it relates to longevity or optimal human performance. There's very little money available for that type of work, and well-controlled nutrition studies on humans are expensive.