Eating grapes may cause an increase in blood sugar. Grapes have a glycemic index of 43, making them a low glycemic index fruit, and they are rich in vitamins, minerals and other nutrients. However, grapes contain a certain amount of sugar and calories, so both healthy people and diabetics should eat grapes appropriately. If diabetics consume too much grapes, it may cause an increase in blood sugar. It should be noted that raisins contain a large amount of sugar, which may cause fluctuations in blood sugar when consumed by diabetic patients, and therefore are not recommended for diabetic patients. Patients who have been diagnosed with diabetes should control their diets, consume reasonable amounts of energy and exercise moderately, monitor their blood glucose, and standardize their glucose-lowering therapy under the guidance of their doctors.