We definitely do not allow questions about long-term effects of food on your body (aka health and nutrition), for a lot of very good reasons - notably, the science is often very unclear, so they tend to solicit opinions and sketchy answers, and not a lot of expert knowledge from cooks.
However, people also sometimes ask about short-term effects, for example whether a food is edible, or will have some mild undesirable effects:
- (migrated) https://cooking.stackexchange.com/questions/77007/is-aquafaba-readily-digestible
- (closed) Can we digest raw starch?
- What can I do to help prevent flatulence from beans?
- How does adding baking soda to soaking beans/lentils reduce the gas they make you have?
- Can bitter almonds(or other nuts containing amygdalin) be made edible?
- Are nectarine seeds edible?
- Are avocado seeds edible?
- Is methyl cellulose edible?
- Are bay leaves dangerous to (unwittingly) eat?
What questions in this vein, if any, should be on-topic? If any are, how do we decide where to draw the line?
The fact that we haven't closed most of those examples suggests that people aren't terribly opposed to them, but a strict reading of overall policy (no health questions) suggests they might be off-topic. Some relevant previous meta questions:
- Closing for "nutrition or health"--where is the boundary? (the focus of the question is on questions clearly about nutrition/health, but an answer does say "what a specific food does to your body after you eat it: close")
- Should we answer questions about biology, if they are food-related? (+4/-1 in favor of allowing biology questions with culinary relevance)
- Is it okay to mention nutrition in a question? (it's okay to mention it as background, just not to ask about it)
(Please feel free to edit more of those in; I haven't done a careful search.)