Yes eating too many grapes can be bad for you and when you eat too many grapes it can cause weight gain as well as diarrhea, stomach cramping etc.
In moderation grapes are very healthy for you though and grapes contain antioxidants, vitamins and nutrients that our bodies need to stay healthy.
The grapes when eaten daily may even ward off cancer and other diseases as well as boost your bodies immune system which may help prevent cold and flu viruses as well.
Grapes do make you poop because the grapes are pretty high in fiber.
The grapes contain most of the fiber in the skin of the grape but also in the rest of the grapes as well.
When you eat foods such as grapes with a lot of fiber then you can get a bowel movement soon after as well.
Also if you eat too many grapes you may get a stomach ache, stomach cramping, stomach bloating and even possibly diarrhea.
I once ate 3 bowls of grapes in one day because I love grapes and that was a mistake because the next day I was on the toilet with diarrhea most of the day.
The same day I had bloating and stomach cramps but the next day I got diarrhea.
But eating a bowl of grapes or two bowls of grapes per day or every other day is healthy and although you still will poop after eating grapes you shouldn't get diarrhea from that amount of grapes.