Glycemic Load
Glycemic Load — Glycemic load (GL) is a measure of the total impact of a food's carbohydrate content on blood glucose, accounting for both the carbohydrate quality (glycemic index) and the quantity consumed in a typical serving. GL is calculated as the glycemic index multiplied by grams of available carbohydrate per serving, divided by 100.
What is glycemic load?
Glycemic load (GL) corrects a major weakness of the glycemic index: GI is measured at a fixed 50-gram carbohydrate portion, but real-world servings vary widely. Watermelon, for example, has a high GI (~76) but a low GL per serving (~4) because a typical serving contains relatively little carbohydrate by weight.
GL is calculated as:
GL = (GI × grams available carbohydrate per serving) / 100
A food with GI 70 and 30 grams of carbohydrate per serving has a GL of 21 (high). A food with the same GI 70 but only 5 grams of carbohydrate per serving has a GL of just 3.5 (low).
How is GL classified?
Per the standard Harvard T.H. Chan School of Public Health classification:
- Low GL: 10 or less per serving
- Medium GL: 11-19 per serving
- High GL: 20 or more per serving
A daily diet with a total GL below approximately 100 is considered low; above 120 is considered high.
Why glycemic load matters
GL is more practically relevant than GI for everyday meal planning because it reflects what people actually eat. A piece of fruit with a moderate GI but small carbohydrate quantity will produce a smaller blood glucose excursion than a large serving of pasta with a similar GI.
For people with type 2 diabetes, prediabetes, or PCOS-related insulin resistance, choosing meals with a lower total GL is associated with more stable postprandial glucose and modest improvements in HbA1c. For weight management in metabolically healthy adults, GL is a useful but secondary consideration; total calorie intake and macronutrient balance remain primary. See also net carbs for a related concept.