Can I ask questions regarding health side effects due to cycling in bicycles.stackexchange.com?
For example about the cramps, saddle sores, etc.
Can I also ask about the diet before and after a cycling session?
Each site has its own Meta, which is where you should ask questions specific to that site.
After reviewing their FAQ page, if you are still unclear about whether a question would be on topic, bring this up on the Bicycles Meta. Users of Bicycles are much better equipped to answer questions about scope than the average user on this site.
If you're not quite sure if your question is on topic, consider looking at meta questions tagged [on-off-topic] where the community has discussed what questions are appropriate for this site.