Rather than restricting diet across the board, just cutting protein had the same effects, whereas fat or carbohydrate restriction alone affected neither free radical formation nor longevity. In turn, the beneficial effects of protein restriction on mitochondrial function were found to be due to the drop in the single amino acid methionine.1473 Restricting all dietary amino acids except methionine had no effect on mitochondrial free radical flux or DNA damage, but restriction of just methionine did both.
