How glycemic load adds the portion
Glycemic load, or GL, combines GI with the amount of available carbohydrate in a serving. The University of Sydney’s explanation of GL gives the calculation: multiply the GI by carbohydrate grams in the portion, then divide by 100.
Consider an imaginary food with a GI of 60. A portion containing 15 grams of available carbohydrate has a calculated GL of 9: 60 × 15 ÷ 100. If the portion contains 30 grams, the calculated GL becomes 18. The food’s GI has stayed the same; the amount eaten has changed.
This is an illustration, not a tested serving recommendation. A GL of 18 does not mean blood glucose will rise by 18 mg/dL. Neither number can predict an individual’s exact reading after eating.
Real meals also contain combinations of foods. Preparation, processing, and the other nutrients in a meal can affect the response. NHS Scotland’s GI guidance emphasizes that the amount of carbohydrate matters and that a high-GI food can still contribute useful nutrients. These limitations are reasons to consider the whole meal rather than judge a food from one number.
