Health⏱ 5 min read
Glycemic Index and Glycemic Load: What the Numbers Mean
The glycemic index tells you how fast a food raises blood sugar — but glycemic load tells you how much it actually matters in a real serving. Here's how to use both correctly.
Glycemic index (GI) is frequently misused — people avoid carrots because they have a high GI, while ignoring that a realistic serving of carrots has a negligible effect on blood sugar. Glycemic load fixes this problem.
What Glycemic Index Measures
GI = How quickly a food raises blood sugar compared to pure glucose
Scale: 0-100 (glucose = 100)
Low GI: below 55
Medium GI: 56-69
High GI: 70 and above
GI is measured using a 50g carbohydrate portion — regardless
of how much of that food you'd actually eat in one sitting.
The Problem with GI Alone
Watermelon GI = 72 (high)
Watermelon carbs per 100g = 8g
To get 50g of carbs from watermelon: 625g (about 6 cups)
Nobody eats 625g of watermelon in one sitting.
A realistic 150g serving contains only 12g of carbs.
This has a minimal blood sugar effect — GI alone misled you.
Glycemic Load: The Better Metric
GL = (GI x Carbohydrates per serving in grams) / 100
Low GL: 0-10
Medium GL: 11-19
High GL: 20+
Watermelon (150g serving):
GL = (72 x 12) / 100 = 8.64 — LOW
White rice (150g cooked serving, 36g carbs, GI 73):
GL = (73 x 36) / 100 = 26.3 — HIGH
GI and GL for Common Foods
FoodGICarbs/servingGL
White bread (1 slice)7514g10.5
Brown bread (1 slice)5012g6.0
White rice (150g cooked)7336g26.3
Basmati rice (150g cooked)5735g20.0
Pasta (180g cooked)4941g20.1
Oats porridge (250g)5527g14.9
Apple (120g)3614g5.0
Banana (ripe, 120g)6223g14.3
Potato (boiled, 150g)7827g21.1
Sweet potato (150g)6128g17.1
Lentils (150g cooked)2920g5.8
Chickpeas (150g cooked)2827g7.6
What Lowers the GI of a Meal
GI is not fixed — it changes based on how food is prepared and combined:
- Fat and protein: Eating carbs alongside fat or protein slows digestion, lowering effective GI
- Cooking and cooling: Cooked and cooled pasta or potatoes have lower GI than freshly cooked (resistant starch forms)
- Acid: Vinegar, lemon juice, and sourdough fermentation all reduce GI
- Particle size: Whole grains have lower GI than ground flours, which is why bread has higher GI than the whole grain it's made from