Watermelon is safe, even in large quantities. Unless you are allergic to watermelon, you can safely consume it. Men with diabetes should consult their doctor about the safe amount of watermelon they can consume. Watermelon as a natural aphrodisiac and other fruits can raise blood sugar, so consuming large amounts can be dangerous for some diabetics. Watermelon is low in calories, but excessive consumption of any food can lead to weight gain.