Glycemic index versus load

Glycemic index ranks foods from 0 to 100 based on how quickly they raise blood sugar compared to pure glucose. Watermelon has a glycemic index of around 72, which sounds alarming until you realise it is 92 percent water. To consume enough carbohydrate from watermelon to meaningfully spike your blood sugar, you would need to eat an implausible quantity of it. Glycemic index is measured using a fixed amount of digestible carbohydrate from each food, which does not reflect how foods are actually eaten. It tells you how fast the carbohydrate travels. It does not tell you how much of it you are consuming.

What is happening

Glycemic load corrects for this by multiplying the glycemic index by the actual grams of carbohydrate in a typical serving and dividing by 100. A food with a high glycemic index but a small carbohydrate content per serving has a low glycemic load. Watermelon's glycemic load per typical portion is around 5, which is low. A bowl of white rice has a glycemic load of around 26, which is high. The difference matters when you are making food choices based on blood sugar impact, because glycemic index alone would mislead you in both directions.

The foods with consistently high glycemic loads in typical serving sizes are white bread, white rice, regular pasta, sweetened drinks, processed breakfast cereals and pastries. These are also the foods that dominate the quick meal and airport food environments that hospitality workers and frequent travellers navigate constantly. Choosing the lower glycemic load option in those environments, a protein and vegetable-based meal over a sandwich, still water over juice, oats over cornflakes, makes a measurable difference to blood sugar response and the energy stability that follows.

What to do next

Fat, protein and fibre all lower the glycemic load of a meal by slowing gastric emptying and reducing the speed at which glucose enters the bloodstream. This is why the composition of a meal matters more than the glycemic index of any single component within it. A potato eaten alone behaves differently from a potato eaten with olive oil, protein and vegetables. Thinking about meals rather than individual foods is the practical application of this, and it is a more useful framework than memorising glycemic index numbers for individual ingredients.

Sources: WHO healthy diet guidance, EUFIC healthy eating guidance, EFSA water guidance, WHO physical activity guidance.

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