You can eat it, but watermelon has a high glycemic index and you need to control the total amount.
The reason for the rumor that you can’t eat watermelon with diabetes is probably related to its high glycemic index. The GI is a concept in nutrition that reflects the speed and ability of a food to raise blood sugar compared to glucose. The glycemic index of glucose is usually set at 100 as a reference standard. Generally speaking, a GI greater than 70 is a high GI food, 55-70 is a medium GI food, and less than 55 is a low GI food. The glycemic index of foods is influenced by a number of factors.
Watermelon has the highest glycemic index of any fruit (GI of 72) and rises sugar quickly. However, because the sugar content is not high, the effect on blood glucose levels is not considered significant when consumed in small amounts. However, diabetics need to be aware that they should try to eat no more than 100 grams of watermelon at a time and no more than 350 grams a day.