Fasted healthy volunteers eat a food with 50g available carbohydrate (total carbs minus fiber); the 2-hour blood glucose area under the curve is compared to pure glucose (=100).Jenkins 1981. Key: only 5-10 people per group — a small-sample average.
2 · High vs low GI curves
High- foods (white bread, glucose) spike fast and crash; low-GI foods (legumes, whole grains) rise gently with lower peaks.The area under the curve (not the peak) is the glycemic index () metric — it captures both height and duration.
3 · GL multiplies in the portion
multiplies by the available carbohydrate in a real serving, so watermelon, with a high GI but few carbs per serving, has a low GL.Watermelon has ~72 (high), but one serving has only 6g available carb — = GI × carbs/100 ≈ 4 (low). GI uses a fixed lab carb dose; GL approximates your actual glycemic load.
4 · You are not the average
For the same food, glycemic response varies widely between individuals — driven by insulin sensitivity, microbiome, processing, and co-ingested fat/protein/fiber.Matthan 2016, using standardized white-bread tests (serum glucose, not ), found inter-individual CV ~25% and intra-individual ~20%. GI/ is a lens, not a law.