The glycemic index, in plain English
Why two foods with the same carbs can give you totally different energy — and when GI actually matters.
What the glycemic index measures
The glycemic index (GI) ranks carbohydrate foods from 0–100 by how quickly they raise blood sugar compared to pure glucose. High-GI foods (70+) spike blood sugar fast; low-GI foods (55 or under) release energy more gradually. White bread sits around 75; an apple around 36.
Fast isn't automatically bad and slow isn't automatically good — it depends on what you're doing. A fast spike is exactly what you want mid-marathon; it's not what you want at your desk at 3pm.
Why GI alone is misleading
GI is measured on a fixed 50g-of-carbs portion, which ignores how much of a food you actually eat. Watermelon has a high GI (~76) but so little carbohydrate per slice that its real-world impact is small.
That's why glycemic load (GL) is the better number. GL = GI × grams of carbs per serving ÷ 100. It captures both speed and quantity. A GL under 10 is low, 11–19 is medium, 20+ is high.
How to use it for steady energy
If your goal is even, all-day energy — no spikes, no 3pm crash — favor lower-GL choices and pair carbs with protein, fat or fiber, all of which blunt the blood-sugar response. Oats, berries, legumes, yogurt and whole fruit are your friends.
Every food in our database shows its GI, glycemic load and a low/medium/high read, so you can build meals around the response you want.
Frequently asked
Is a high-GI food always unhealthy?+
No. Context matters. High-GI carbs are ideal during and right after hard exercise when you want fast glycogen replenishment. The 'avoid high-GI' advice is really about everyday, sedentary eating.
What's the difference between GI and glycemic load?+
GI measures speed for a fixed carb amount; glycemic load (GL) also factors in how many carbs are in a real serving. GL is the more practical number.
Does cooking change GI?+
Yes — cooking, ripeness and processing all raise GI. Al dente pasta is lower-GI than soft; a green banana is lower than a brown one.