Glycemic index (GI) measures how quickly the carbs in a food raise blood glucose, on a 0-100 scale anchored against pure glucose. Glycemic load (GL) corrects for the fact that GI tests use a fixed 50g carb portion, which is not the amount in a typical real serving.
The math: GL = (GI × grams of available carbs in a serving) / 100.
Examples that show why GL beats GI in practice:
- Watermelon has a high GI (around 76), which sounds bad. A typical serving of watermelon contains only about 11g of carbs. The GL of a serving is about 8 — low.
- White rice has a moderate-to-high GI (around 73). A typical 1 cup serving of cooked white rice contains 45g carbs. The GL is about 33 — high.
- Carrot has a moderate GI (around 47). A typical serving has 5g carbs. The GL is about 2 — very low.
GL classification (rough thresholds, varies by source):
- Low GL: under 10
- Medium GL: 11-19
- High GL: 20+
For non-diabetic populations, glycemic load is more useful than GI because it reflects what actually happens at typical eating portions. For people managing diabetes, blood glucose response is influenced by GL, total carb amount, fiber content, fat content, and the rest of the meal — GL alone is a useful but incomplete signal.
The mainstream-nutrition take: glycemic load is a useful tiebreaker between similar foods, but it is not a primary lever for weight loss in non-diabetic populations. Calorie balance, protein adequacy, and fiber intake matter more for body composition outcomes than chasing low-GL foods.