Glycemic Load vs. Glycemic Index: What's the Difference?

Q: Which should you use — GI or GL?

Glycemic load is more useful for practical decisions. It answers the question you actually care about: "How much will this specific portion raise my blood sugar?"

Q: What are the best foods by glycemic load?

Very low GL (0–5): - Most vegetables (broccoli, spinach, peppers, tomatoes) - Nuts (almonds, walnuts, pecans) - Eggs, meat, fish, cheese - Avocado - Berries (strawberries, raspberries)

TL;DR: Glycemic index (GI) and glycemic load (GL) measure different things — and using only GI can be misleading. GI measures how fast a food’s carbohydrate raises blood sugar, gram for gram. GL accounts for how much carbohydrate is actually in a realistic serving. Watermelon illustrates the distinction perfectly: it has a high GI (76) but a low GL (4 per serving), because a cup of watermelon contains only 11 grams of carbohydrate. The glycemic load is the more practical measure for predicting real-world blood sugar responses.

What is the glycemic index?

The glycemic index is a scale from 0 to 100 that ranks foods based on how quickly their carbohydrate raises blood glucose compared to pure glucose (which is 100).

Low GI: 0–55 (slow, gradual rise)
Medium GI: 56–69 (moderate rise)
High GI: 70–100 (fast, sharp rise)

GI is measured by feeding test subjects a portion of food containing exactly 50 grams of digestible carbohydrate, then measuring blood glucose over 2 hours. The area under the glucose curve is compared to 50 grams of pure glucose.

The limitation: GI only tells you about the quality of the carbohydrate (how fast it digests), not the quantity in a real serving. This is why watermelon (GI 76) appears worse than it actually is — you would need to eat 4–5 cups of watermelon to get the 50 grams of carbohydrate used in the GI test. Nobody eats that much watermelon at once.

What is glycemic load?

Glycemic load combines GI with actual serving size to give a more practical measure:

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

Low GL: 0–10 (small blood sugar impact)
Medium GL: 11–19 (moderate impact)
High GL: 20+ (large impact)

GL answers the question that GI does not: “How much will this actual serving of food affect my blood sugar?”

Why GI alone can be misleading

Food	GI	Carbs per serving	GL	What GI says	What GL says
Watermelon (1 cup)	76 (high)	11 g	4 (low)	Danger!	No problem
Popcorn (3 cups)	65 (medium)	15 g	7 (low)	Moderate concern	Minimal impact
Carrots (1 cup)	71 (high)	8 g	6 (low)	Danger!	No problem
White rice (1 cup)	73 (high)	45 g	33 (high)	Danger!	Yes, big spike
Baked potato	85 (high)	33 g	28 (high)	Danger!	Yes, big spike
Spaghetti (1 cup)	49 (low)	43 g	21 (high)	Seems safe	Actually large impact
Peanuts (1 oz)	7 (low)	2 g	0 (very low)	Very safe	Confirmed safe

The most instructive examples:

Watermelon and carrots have high GIs that would suggest they are bad for blood sugar. But their glycemic loads are low because a serving contains very little carbohydrate. GI overestimates their impact.

Pasta has a low GI that suggests it is safe for blood sugar. But a typical serving contains 43 grams of carbohydrate, giving it a high glycemic load. GI underestimates its impact.

Which should you use — GI or GL?

Glycemic load is more useful for practical decisions. It answers the question you actually care about: “How much will this specific portion raise my blood sugar?”

However, both metrics have value:

Use GI when:

Comparing two foods gram-for-gram (which type of bread/rice/cereal is better?)
Choosing between two similar foods in the same category
Understanding the inherent digestibility of a carbohydrate

Use GL when:

Deciding whether a specific portion will spike you
Planning a meal’s total glycemic impact
Evaluating foods that have high GI but low carb density (watermelon, carrots)

The best approach: Use GL for meal planning but check GI when substituting within a food category. If you are choosing between jasmine rice (GI 89) and basmati rice (GI 58), GI tells you basmati is inherently slower. Then use GL to decide how much to serve.

How to calculate glycemic load for any food

The formula is simple:

GL = (GI × net carbs per serving) ÷ 100

Examples:

Apple: (36 × 21 g) ÷ 100 = GL 8 (low)
Banana: (51 × 24 g) ÷ 100 = GL 12 (medium)
White rice (1 cup): (73 × 45 g) ÷ 100 = GL 33 (high)
Almonds (1 oz): (0 × 2.5 g) ÷ 100 = GL 0 (very low)

A meal’s total glycemic load is approximately the sum of the GLs of each component. A meal with a combined GL under 20 will generally produce a moderate, manageable glucose response.

What are the best foods by glycemic load?

Very low GL (0–5):

Most vegetables (broccoli, spinach, peppers, tomatoes)
Nuts (almonds, walnuts, pecans)
Eggs, meat, fish, cheese
Avocado
Berries (strawberries, raspberries)

Low GL (6–10):

Most whole fruits (apples, oranges, peaches)
Legumes (lentils, chickpeas)
Greek yogurt (plain)
Popcorn (3 cups)

Medium GL (11–19):

Banana
Oatmeal (1 cup cooked)
Quinoa (1 cup cooked)
Sweet potato (boiled, medium)

High GL (20+):

White rice (1 cup cooked): GL 33
White bread (2 slices): GL 20
Pasta (1 cup cooked): GL 21
Baked potato: GL 28
Most cereals (1 cup): GL 20–30

Key takeaways

Glycemic index measures how fast a food’s carbs spike blood sugar. Glycemic load measures how much a real serving actually spikes.
GL = (GI × carbs per serving) ÷ 100.
Watermelon (GI 76, GL 4) and carrots (GI 71, GL 6) have high GI but low GL — they barely spike blood sugar.
Pasta (GI 49, GL 21) has low GI but high GL — a typical serving contains lots of carbs.
GL is more practical for everyday decisions. GI is useful for comparing foods within a category.
A meal with total GL under 20 generally produces a manageable glucose response.
Foods with both low GI and low GL (nuts, non-starchy vegetables, berries) are the best choices for blood sugar.

Sources

Foster-Powell, K., Holt, S.H., & Brand-Miller, J.C. (2002). International table of glycemic index and glycemic load values. American Journal of Clinical Nutrition, 76(1), 5–56.
Atkinson, F.S., Foster-Powell, K., & Brand-Miller, J.C. (2008). International tables of glycemic index and glycemic load values: 2008. Diabetes Care, 31(12), 2281–2283.
Brand-Miller, J.C., et al. (2003). Low-glycemic index diets in the management of diabetes: a meta-analysis of randomized controlled trials. Diabetes Care, 26(8), 2261–2267.
Ludwig, D.S. (2002). The glycemic index: physiological mechanisms relating to obesity, diabetes, and cardiovascular disease. JAMA, 287(18), 2414–2423.