What Is Glycemic Index (GI) and Glycemic Load (GL)? — Complete Explainer
Glycemic Index: Speed of Blood Sugar Rise
GI measures how fast a food raises blood glucose compared to pure glucose (GI = 100). Low GI: ≤55. Medium GI: 56–69. High GI: ≥70. GI is measured with a 50g carbohydrate portion — but the GI of a food doesn’t tell you the effect of a realistic serving size.
Glycemic Load: The Better Metric
GL = (GI × grams of carbohydrate per serving) ÷ 100. Watermelon has a high GI (72) but low GL (4) because a typical serving contains only 5g of carbohydrates. White rice has GI of 73 and GL of 29 (for 150g cooked). GL under 10 is low; 11–19 is medium; 20+ is high.
Why Both Numbers Are Needed Together
GI alone leads to misleading conclusions (watermelon is ‘bad’ because its GI is high, but its GL is negligible). GL alone can miss rapid blood sugar spikes from high-GI foods in large quantities. Use GI to identify which foods spike blood sugar fast, and GL to estimate the real-world impact of a realistic serving.
Practical Application
Replacing high-GI, high-GL carbohydrates with lower alternatives reduces post-meal blood sugar peaks, improves insulin sensitivity, and supports fat loss (lower insulin = less fat storage signaling). Use Glycemic Index Lookup to check specific foods.
Frequently Asked Questions
Look up glycemic index values
Open Glycemic Index Lookup to find the GI and GL of any food.
Open Glycemic Index