What happens if I eat right before I go swimming?

There's some truth behind this, despite what some people may say. The reason you should give about a half hour to an hour in between eating and swimming is because, when you eat, the majority of your blood is pumping nutrients to your digestive system. If you swim immediately after eating, you won't have as much energy because your muscles are not getting as much nutrients as they would if you wait.

If you're looking for the actual science behind it, here it is. You have 2 divisions of your nervous system known as the sympathetic and paradympathetic nervous system. Your parasympathetic is very active when you eat and sleep and rest, meaning your blood will prioritize body systems like the urinary and digestive system. When you are active, the sympathetic is stimulated, and the majority of your blood nutrients will go to your muscles. If you saw in immediately after eating, your blood won't all prioritize your muscles because it is still working on digesting.

You want the real reason? It's because people who eat and drink before getting into a swimming pool tend to pee and poop.

I've never heard about throwing up. I always heard you might get cramps.

I actually just read that it was a myth! If you eat, and then work out, then you might be sick. But if you're working out, and doing hard swimming, then you might actually get sick.