Glycemic Load

Glycemic load (GL) is the glycemic-index concept applied to a real-world portion. Where GI tells you how glucose-raising a food is per gram of available carbohydrate, GL tells you how glucose-raising a serving of that food actually is.

The formula

GL = (GI × grams of available carbohydrate per serving) ÷ 100

"Available carbohydrate" excludes fibre — the same value used in "net carbs" tracking. This matters: a food can be high in total carbohydrate but low in available carbohydrate if it's fibre-rich.

Why portion correction matters

Watermelon is the canonical example. It has a high GI (around 72) because the sugar in watermelon is rapidly absorbed. It has a low GL (about 5 per typical 120 g serving) because watermelon is mostly water — a serving contains only about 7 g of available carbohydrate. In practice, a reasonable portion of watermelon produces a modest glucose response, consistent with the GL number, not the GI number.

Conversely, white rice has a GI of around 73 and a GL of around 23 per 150 g cooked serving. Same GI as watermelon, four times the GL, four times the glucose response.

GL ranges

• Low: GL ≤ 10 per serving
• Medium: GL 11–19
• High: GL ≥ 20

Common low-GL foods per serving: legumes, most whole fruits, non-starchy vegetables, nuts, minimally-processed dairy, eggs. Common high-GL foods: large servings of white rice/white bread/pasta, sugar-sweetened beverages, most processed breakfast cereals.

What GL still doesn't capture

GL is a per-food calculation. Real meals rarely contain one food in isolation. Co-ingested fat, protein, and fibre all reduce the effective glycemic response to a carbohydrate food — sometimes substantially. A 30 g serving of white rice eaten with 150 g chicken breast, olive oil, and broccoli produces a very different glucose curve than 30 g white rice eaten alone. Neither GI nor GL captures this meal-level modulation.

When to use GL

• Diabetes management. More clinically relevant than GI for matching carbohydrate choices to glucose targets and insulin regimens.
• Meal planning for steady energy. Lower total meal GL is associated with less post-meal drowsiness and steadier perceived energy.
• Comparing foods for tracking purposes. Between two items of similar calorie content, the lower-GL option typically produces a gentler blood-glucose curve.

Limitations worth acknowledging

Published GL tables use standardised reference portions and average GI values. The actual glycemic response of an individual to a specific food on a specific day varies with recent meals, sleep, stress, physical activity, and microbiome composition. Personalised glucose-response tracking via a continuous glucose monitor (CGM) routinely shows individual variation that makes the population-average GL number useful as a starting hypothesis but not as ground truth.