Elsethread another poster was downvoted for saying it[0], but amphetamines make it much easier to get so focused on a task you forget to eat. I experimented with it for a while and even I, a food addict, forgot to eat if I was truly engaged in something.

[0] Probably because his tone was accusational, though anyone who thinks chess grandmasters are any less willing to use performance drugs than any other high-end athlete is kidding themselves.