Too much of anything (even a good thing) can be harmful. There should be a balance. Yes, you should try to incorporate fruits and veggies in your daily diet. BUT…if that’s the only thing you’re eating…how will you compensate for the other building blocks that your body needs such as protein and minerals like iron and zinc (which can be found in meat and dairy)?
I’ve read that eating excessive amounts of a particular vitamin can cause problems. Too many carrots, I’ve heard, can make your skin orange/yellow. Excessive vitamin A can cause temporary symptoms like fatigue, weakness, vomiting, etc.
Sometimes vitamins/minerals can either enhance or impede the effect of another vitamin or mineral. For example…milk can hinder the absorption of iron whereas vitamin C enhances it. An excessive amount of iron can cause a deficiency in zinc.
And you don’t have to eat until you’re totally full…but full enough. Drinking water is a good way to not only keep yourself hydrated but makes you feel fuller. I’m guilty of overeating as well…and many health problems can result from this. There’s a hadith where the Prophet SAWS said keep 1/3 of your stomach for food, 1/3 for water/and 1/3 for air.