What Is the Glycemic Index?
The Glycemic Index (GI) ranks carbohydrate-containing foods by how quickly they raise blood glucose levels on a scale of 0–100. Pure glucose is 100. Foods are classified as:
- Low GI (55 or less) — slow, gradual blood sugar rise. Best for sustained energy and blood sugar management.
- Medium GI (56–69) — moderate blood sugar impact.
- High GI (70+) — rapid blood sugar spike followed by crash. Worst for energy stability and insulin resistance.
Low-GI Foods List
| Food | GI Score | Category |
|---|---|---|
| Lentils | 29 | Legumes |
| Chickpeas | 33 | Legumes |
| Kidney beans | 24 | Legumes |
| Steel-cut oats | 42 | Grains |
| Sweet potato | 44 | Starchy vegetable |
| Quinoa | 53 | Grains |
| Whole wheat pasta | 42 | Grains |
| Apples | 36 | Fruits |
| Oranges | 43 | Fruits |
| Berries | 25–40 | Fruits |
| Cherries | 22 | Fruits |
| Plain yogurt | 14 | Dairy |
| Milk | 31 | Dairy |
| Nuts (all types) | 15–25 | Nuts/Seeds |
| Most non-starchy vegetables | 10–20 | Vegetables |
High-GI Foods to Limit
| Food | GI Score |
|---|---|
| White bread | 75 |
| White rice | 73 |
| Russet potato (baked) | 78 |
| Cornflakes cereal | 81 |
| Instant oatmeal | 79 |
| Watermelon | 76 |
| Pretzels | 83 |
| Rice cakes | 82 |
Glycemic Load: The Better Metric
The GI has a flaw: it measures blood sugar impact per 50g of carbohydrates, regardless of typical serving size. Watermelon has a high GI (76) but you would need to eat 5 cups to get 50g of carbs. The Glycemic Load (GL) accounts for serving size: GL = GI x grams of carbs per serving / 100. A GL under 10 is considered low. Watermelon has a GL of only 8 per typical serving, making it fine for blood sugar.
Practical Strategies for Blood Sugar Control
- Pair carbs with protein or fat — eating carbs alone spikes blood sugar. Adding protein or fat slows absorption (e.g., apple + peanut butter vs. apple alone).
- Eat vegetables first — research shows eating vegetables before carbs reduces post-meal blood sugar by 20–30%.
- Choose whole grains over refined — steel-cut oats (GI 42) vs. instant oats (GI 79); whole wheat bread (GI 51) vs. white bread (GI 75).
- Walking after meals — a 10–15 minute walk after eating reduces blood sugar spikes by up to 30%.
- Add vinegar — 1–2 tablespoons of vinegar (in dressing or diluted in water) before a meal reduces post-meal blood sugar by 20–35% in studies.