Why do I get gas from onions?

[healthmi]

If I eat onion once in a while, I would get diarrhea from eating it. If I eat it often, I would build up tolerance and only get gas. But that's the best case; I cannot be completely unaffected.

Onion is not the only trigger; garlic, and other stuff also gives me gas but I haven't narrowed down all of them. I'm in my 50s and this problem has plagued me for maybe 20 or more years. I don't have this issue when I was in college or earlier.

What might be the problem? Can I narrow it down myself? Is there some tests I can ask my doctor to perform?

[CurfewX]

That's not uncommon, and there's no reason to test for it since it's a well-known phenomenon that onions, along with several other foods, can cause gas in many people: https://www.yorktest.com/10-surprising-foods-that-give-you-bloating-and-gas/

[healthmi]

Thanks for the list. I'm sure I get gas from alot more food than the list because I seem to always be holding in my gas in any public gatherings, which cause pain eventually.
Since I developed the problem when I got old, is there no cure, supplement, etc? I tried beano but didn't seem to work.