Nutrition's also entangled with a horrific mess of body-image issues and cultural expectations. These aren't essential to any of the strains of cultural criticism that they intersect, so I don't think I'd call them ideological; but because they're so closely linked to people's identities, they exhibit a lot of the problems we associate with ideology.

Same goes for related fields like exercise. The mind-killer here doesn't metastasize like ideology tends to, but it's every bit as pathological if you accidentally end up poking one of its hosts in the wrong spot.