Cellular organs are a pretty untouchable class of things for anything humans are going to do on a macro-scale. If you're proposing to achieve a big effect from say, a diet, then focusing on more then 1 bodily component is suspicious because there's a huge range of barriers you need to get through to get to it (without damaging, generally).

There are lots of drugs, for example, which are useless because although they target the right protein and have the desired effect they can't actually get to it via normal metabolism and the like.