Although not precisely a food in the true sense of the word, but enough people drink coffee and treat it as a meal for it to count. It's extremely easy to become dependent on caffeine, even needing it in the middle of the day for a burst after the morning dose wears off. However, as a strong stimulant, it has a potentially profound effect on the kidneys. Those who already have worn kidneys are more likely to develop problems with long-term caffeine use. Drinking caffeine increases the rate at which calcium is extracted from the body and makes the user more likely to develop kidney stones later on.