Grapefruit is not a known cause of diabetes. It may be able to help treat diabetes, according to a study from the University of California published in the peer-reviewed journal PLOS One.
Diabetes occurs when the body cannot produce enough of the hormone insulin to regulate blood-sugar levels. In the study, naringenin, the antioxidant responsible for the grapefruit's bitter taste, reduced blood glucose and improved insulin tolerance. However, Aglaee Jacob, a registered dietitian, warns that patients taking prescription drugs should be careful when eating or drinking grapefruit juice because it interacts with many drugs used to control conditions like blood pressure, blood cholesterol levels or depression.