Glycemic index (GI) is one of the most misunderstood numbers in nutrition. Watermelon has a GI of 80 — higher than table sugar — yet eating a normal slice barely moves blood glucose. The reason is glycemic load.
Glycemic index vs glycemic load
- **Glycemic index** ranks how quickly 50g of *carbohydrate* from a food raises blood sugar compared to pure glucose.
- **Glycemic load** is the GI multiplied by the *grams of carbs in an actual serving*, divided by 100.
In other words: GI tells you what kind of carb it is. GL tells you how much you're actually eating.
A worked example
Watermelon: - GI: 80 - Carbs per 120g serving: 9g - GL: (80 × 9) / 100 = 7.2 → low
Bagel: - GI: 72 - Carbs per 100g serving: 50g - GL: (72 × 50) / 100 = 36 → very high
The bagel will spike blood sugar much harder than the watermelon, even though the GI numbers are close.
How to use glycemic load in practice
- GL of 1-10: low, safe for most meals
- GL of 11-19: moderate, pair with protein and fat
- GL of 20+: high, eat sparingly or split across the day
Why Carb Lens reports both
The scanner estimates glycemic load for every meal because it's a better real-world predictor than GI alone. The "blood sugar impact" tag (low / moderate / high) on each scan combines GL with portion size, fiber and protein to give a single, glanceable answer.