For some people it's not too bad. I can eat a lot before anything happens, Minato-san might be the same. But if you eat too much you can get a stomach ache, which doesn't feel nice at all. Like moving and everything is an effort, and if you do too much you feel like you're going to pass out.

[There's other parts to it too, but he's making an effort to put it in a way he thinks Aigis will understand. He doesn't want to confuse her after all]