Glycemic Load vs Glycemic Index: Which Number Should You Use?

If the glycemic index has ever given you an answer that felt wrong, this is why.

The difference in one sentence

Index measures how fast the carbohydrate in a food raises blood glucose. Load measures what a real portion of that food actually does.

The watermelon problem

Watermelon has a high glycemic index — around 75. By index alone it belongs beside white bread.

But watermelon is mostly water. A normal slice contains very little carbohydrate, so its actual effect is small. High index, low load.

The reverse also happens. Some foods with unremarkable index scores are eaten in large enough quantities that the load is substantial — pasta being the obvious one.

How load is calculated

Glycemic index multiplied by the grams of carbohydrate in your portion, divided by 100.

• 10 or below — low
• 11 to 19 — medium
• 20 and above — high

You do not need to do this arithmetic. You need to know it exists, because it explains why index tables occasionally mislead.

The practical version

Two questions instead of a calculation:

How fast is this form of the food? Steel-cut or instant. Dense or airy. Whole or pureed.

How much of it am I actually eating?

Get both roughly right and you've captured what glycemic load formalizes.

Why the index still matters

Because within a category, it's the useful comparison. Basmati versus short-grain rice, sourdough versus soft white, steel-cut versus instant — same food, same portion, different speed. That's where index earns its keep.

Load is what stops you being frightened of watermelon.

Try this week: pick one food you've been avoiding on index alone and check whether the portion you'd actually eat contains much carbohydrate. Several "forbidden" foods aren't.

Education, not medical advice.