I have a healthy diet and I excercise a lot, but I have horrible gas! What are possible reasons and how can I stop it? Are there things to eat that help prevent gas?
Ever thought of GAS X? And it isn’t what you should, but what you shouldn’t eat. Like beans…seriously. 
One thing to check is your tolerance for dairy. Some people don’t digest dairy products well (or at all) once they’re adults, and one of the symptoms is frequent and horrible-smelling gas. Eliminate all milk, cheese, and stuff from your diet for a week. If the gas goes away that’s the problem. In which case, if you still want to eat the stuff, you can buy tablets that let you digest this stuff again.
If you eat a lot of gas-producing vegetables (beans, cabbage, califlower, etc.) try beano.
It’s almost always one of those two culprits.
My vegetarian relatives (who, of course, eat a lot of beans) assure me that seaweed also helps to keep the gas down. Then again, it might just be that their digestive systems are more used to it.