Definition
Portion size is the amount of a food you actually eat in one sitting — the difference between “one serving” on a label and what ends up on your plate. For blood glucose, it is often the single biggest lever you control, because doubling the carbohydrate doubles the expected response.
Why Portion Outranks GI
Glycemic load exists precisely because of this:
GL = GI × available carbohydrate per serving ÷ 100
Halving the portion halves the GL. The food’s GI doesn’t change — the impact does. A small portion of a high-GI food (a cup of watermelon) can produce less glucose than a large portion of a low-GI food (three cups of lentils). “Good food, bad food” framing collapses the moment portions are on the table.
Common Portion Distortions
- Restaurant servings of rice, pasta and bread are routinely 2–3 servings.
- Snacks without boundaries — chips, nuts, grapes — disappear by the handful; the amount eaten isn’t a decision, it’s a container.
- Labels define serving sizes differently — compare like with like, never label number to label number across products.
Practical Portion Anchors
- Fruit: one medium piece, or one cup of chopped fruit.
- Starch: about a cup of cooked rice/pasta, or one medium potato — start lower if your meter says so.
- Nuts: one small handful (about 30 g).
- Visual: a cupped hand ≈ 1 serving of starch; a palm ≈ a protein serving.
In short: portion size is the amount you actually eat — and because GL scales with it, it is the most direct control you have over a meal’s glucose response. See the per-serving GL on every food page.