Watermelon and diabetes are possible only if the watermelon is eaten in moderation. Diabetic people usually self manage their blood glucose levels by monitoring their own carbohydrate intake, for example, by counting the grams of carbohydrate in a particular fruit.
Glycaemic index is the food classification according to how quickly a particular carbohydrate raises the blood glucose levels (or how quickly the carbohydrate turns into sugar). The higher the glycaemic index number, the greater the blood sugar response. Foods with a glycaemic index of 70 or more are said to be ‘high'; glycaemic index of between 55 and 70 are ‘moderate’ and a glycaemic index of less than 55 are said to be ‘low’.
However, a better indication of how quickly the effect of a standard portion of the food (for example, watermelon) raises your blood glucose is the glycemic load. In addition, the glycaemic load is the amount of the carbohydrate food multiplied by that food’s glycemic index. The glycaemic load of a food of more than 20 is said to be ‘high'; between 11 and 19 is ‘moderate’ and if it is 10 or less then it is considered low. Generally, you should try and aim to keep your glycaemic load to below 15.
Watermelon has a high glycaemic index, but the glycemic load per food serving (size of 120g) is only 4, which is relatively low. So unless you intend to eat lots of the watermelon at a particular time, it will not have a big impact on your blood glucose levels. However, due to watermelon being high in sugar, you should still limit the quantity you intend to eat.
If you are a lover of watermelons then remember to monitor your blood sugar levels after eating it, so that you can monitor its affects. If after eating the watermelon, it raises your blood sugar, limit the amount of watermelon you eat next time. Also, you could combine the watermelon with a protein or fat, as this will reduce the speed of sugar absorption.