Watermelon's GI Myth Busted by New University of Sydney Data: A Nutritional Breakdown of Summer's Favorite Cooling Fruit

Watermelon has long carried a somewhat unfair label — a GI (glycemic index) value of 72 to 76, putting it in the "high" category, which made many people watching their blood sugar or body composition wary of it. But new data released by the University of Sydney shows that the average GI value across four watermelon varieties is actually just 50, and based on a 120-gram serving, the glycemic load (GL) is only 4.4 — far gentler than the number most people had in mind.

This fruit is about 90% water. According to Japan's Ministry of Education, Culture, Sports, Science and Technology food composition database, every 100 grams of red-flesh watermelon contains 9.5g of carbohydrates, 0.3g of dietary fiber, 0.6g of protein, and 0.1g of fat, coming in at just 41 calories. Its sugar content is solid, yet its overall calorie count stays low — which is exactly why it satisfies both "craving something sweet" and "keeping portions in check" at the same time.

Beyond Antioxidants and Minerals, These Components Deserve Attention

Watermelon is rich in lycopene, which offers strong antioxidant properties, and also contains citrulline, which may have a positive effect on blood flow and blood pressure. As for minerals, it provides potassium, magnesium, and phosphorus, along with B vitamins, vitamin A, and vitamin C — reasons why many people choose it as a summer hydration source. Beyond water, it also delivers real nutrient density. Vitamin C in particular is closely tied to collagen production, playing a role in maintaining skin and hair health. Its dietary fiber content isn't especially high, but combined with its abundant water content, it still helps boost fullness and support appetite control.

Even during a fat-loss phase, eating watermelon in moderation won't directly cause weight gain. It's low in calories and fat, and its high water content makes it easy to feel full, making it a good choice as a between-meal snack or a light, refreshing dessert. That said, its natural sugars still count toward total intake, so if strict calorie management is your goal, portion size still matters. If you have diabetes or need to monitor your blood sugar, it's best to consult a doctor or dietitian first, avoid eating large amounts at once, and stick to a modest, mindful portion.

Pick a Perfectly Ripe, Sweet Watermelon, Then Turn It Into Refreshing Dishes

The Japan Agricultural Cooperatives (JA Group) offers straightforward selection tips: first check the rind — one with a glossy sheen and clearly defined stripes is preferable; then give it a gentle tap and listen — a firm, crisp echoing sound usually signals ripeness.

When it comes to eating it, watermelon isn't just for slicing and eating straight. Tossing it into a salad with feta cheese and mint, blending it into a smoothie, or swapping bread for watermelon slices to make a "watermelon sandwich" are all popular summer ways to enjoy it. You might also try a simple watermelon-cinnamon dessert: cut a seeded watermelon into two pieces, dice it into a bowl, squeeze in the juice of half a lemon and drizzle it over the top, sprinkle with a small spoonful of cinnamon powder and toss to combine, then finish with fresh mint leaves to taste. Chill before serving — the sweet-tart flavor with a hint of spice makes it perfect for summer.