Insulin resistance is a condition in which the body does not use insulin properly. The pancreas releases the hormone insulin into the bloodstream to help convert glucose, which comes from food, into energy. Because the muscles, liver and cells can't use the insulin effectively, glucose builds up in the bloodstream. Watermelon is high in sugar and can affect blood glucose, but it can also be part of a healthy diet.
The glycemic index, or GI, ranks carbohydrate-containing foods, including beverages, based on how they affect blood glucose. A carbohydrate-containing food is considered high on the glycemic index if it has a value above 70. High-glycemic foods are quickly digested by the body, causing fluctuations in your blood sugar level. High blood glucose and excessive insulin secretion can damage the pancreas and cause Type 2 diabetes. Low-glycemic foods are absorbed more slowly and stay in your digestive track longer. This slower process does not put a sudden demand on the pancreas to release lots of insulin, so blood sugar increases gradually and in a regulated fashion. A balanced blood sugar level can help reduce the risk of insulin resistance.
Watermelon is a nutritious, high-glycemic fruit whose GI value is 72. Watermelon can have the same affect on blood glucose as a bagel, because they have the same GI value. However, the GI of a carbohydrate-containing food is an incomplete assessment and should not be used as the only yardstick for determining foods that can affect blood glucose, according to the University of Wisconsin Health. The glycemic load takes the GI into account, but also measures the quality and amount of carbohydrates in foods. Watermelon has a high GI, but there aren't a lot of carbohydrates, so watermelon's glycemic load is relatively low. You would have to eat a lot of watermelon for it to have a big impact on blood glucose.
Insulin resistance is connected to obesity, hypertension and high levels of fat in the blood. These conditions can increase risk for developing Type 2 diabetes and cardiovascular disease. You might have metabolic syndrome or insulin resistance syndrome if you have several of these risk factors: a waist measurement greater than 40 inches for men or 35 inches for women; blood pressure levels above 130/85 mm Hg; and fasting blood glucose levels above 100 mg dL. Cholesterol levels are important, too; HDL, or "good" cholesterol, should not be below 40 mg dL for men or below 50 mg dL for women.
A 1¼-cup serving of watermelon has 57 calories, 14 g of carbohydrates and 12 g sugar. If you are concerned about how watermelon could affect your blood glucose, eat it with protein, fat or a low-glycemic food such as beans or oatmeal. This will slow the absorption of the glucose into the bloodstream. Speak to a dietitian about concerns of consuming watermelon in the diet.