A measure of insulin response to food, developed to capture what the glycemic index misses.
What the evidence says
- The insulin index was developed by Susanna Holt and colleagues at the University of Sydney[1]
- Measures insulin response directly rather than inferring it from blood sugar[1]
- Uses isoenergetic 1000-kJ (240-kcal) portions of food for standardized comparison; 38 foods across 6 categories tested on groups of 11–13 healthy subjects[1]
- Glycemic and insulin scores were highly correlated (r = 0.70, P < 0.001, n = 38) but not identical[1]
- Protein-rich foods and bakery products (rich in fat and refined carbohydrate) ”elicited insulin responses that were disproportionately higher than their glycemic responses”[1]
- A separate study opens from the premise that milk products ”produce high insulin responses, despite their low GI”. In it, reconstituted milk powder and whey gave glucose areas 62% and 57% below a white-wheat bread reference, the whey meal came with a 90% higher insulin area, and the authors conclude that ”Milk proteins have insulinotropic properties; the whey fraction contains the predominating insulin secretagogue”[2]
- Holt’s across-food correlations point the other way, and both facts are that paper’s own. Across the food set, total carbohydrate (r = 0.39, P < 0.05, n = 36) and sugar (r = 0.36, P < 0.05, n = 36) contents were positively related to mean insulin scores, while fat (r = −0.27, NS, n = 36) and protein (r = −0.24, NS, n = 38) were negatively related — both non-significant. Note the scopes: this is nutrient content correlated across the tested foods — n = 36 for carbohydrate, sugar and fat, n = 38 for protein, against a set of 38 — whereas the disproportionate-insulin finding above is about particular foods measured against their own glycemic response. Different questions, so the two do not contradict[1]