This is an excellent example of how a little information can be misconstrued. I can understand why people are confused, since this is a complicated topic. But, you can rest assured that real foods, such as watermelon, remain good for us despite the glycemic index.
The glycemic index (GI) ranks foods on a scale of 1 to 100 by how quickly they convert to glucose and raise blood sugar levels. For example, pure glucose scores a 100, while peanuts score about 14. The lower the number, the gentler the rise in blood sugar, and the more likely a food will help with weight loss and lower your risk for a host of other ills, including heart disease and diabetes. A diet loaded with high glycemic foods does just the opposite. Many factors influence how fast the body digests a carb-rich food, but in general, the less processed a food, the lower its GI score and the more likely it will improve a person’s health risk and help someone lose weight. The GI is complicated, since a food’s score will change based on other foods at the meal. GI scores also vary from person to person and even fluctuate enormously in the same person from day to day.
Granted, watermelon has a high GI score of 72, but this natural, unprocessed fruit remains a healthful food because of another factor called the “glycemic load.” This factor compares a food’s GI score with the amount of calories and carbs in the food,. The glycemic load is a much better indicator of a food’s ability to prevent or contribute to disease, since a food that has a large amount of carbs AND dramatically raises blood sugar levels obviously increases the chances of weight gain more than a food that might temporarily raise blood sugar levels, but has few calories. A low GL is associated with a lower risk for insulin resistance, metabolic syndrome, and weight gain.
Let’s put this information into real terms. A potato or a corn tortilla have high glycemic scores and pack a hefty dose of carbs, while watermelon has a high GI score, but few calories or carbs. The former will increase the chances of those extra calories being funneled into fat cells, but watermelon just fills you up, without filling you out. The same can be said for other healthful foods, such as carrots. In general, a glycemic load of 10 or less is low, 11 to 19 is medium, and 20 or greater is considered high. For comparison sake, a carrot has a GL of 3.5, watermelon has a GL of 3.6, potatoes have a GL of 18, and a corn tortilla has a GL of 25.
All of this is interesting, but in reality, who wants to memorize a bunch of GI or GL scores?! That’s even worse than counting fat grams and calories. In fact, nations have considered placing GI or GL information on packaged foods and decided against it, siting concerns that those claims would be misleading. Rather than obsess about the numbers, the simple guideline for eating in tune with blood sugar and waistline is to choose lots of wholesome, natural foods, such as watermelon and other fruits and vegetables, whole grains, nuts, legumes, and seafood, which automatically lower the overall GI score and keep a person healthy throughout life.