Glucose tolerance generally refers to the oral glucose tolerance test, if you eat watermelon the day before the oral glucose tolerance test, if you keep enough fasting time will not affect the results. Oral glucose tolerance test can understand the function of pancreatic B-cells and the body’s ability to regulate blood glucose, and can be used to assist in the diagnosis of the presence of diabetes mellitus; the test needs to be kept in a fasting state for 8 to 10 hours, and the daily intake of carbohydrates should be more than 150g for three days before the test. Therefore, as long as you are prepared to fast after eating watermelon the day before the test, it will not affect the test on the following day. People who need to undergo oral glucose tolerance test can consult their doctor if they are not sure about the precautions of the test.