Low glycaemic index
What it is
A way of choosing carbohydrates by how fast they raise blood glucose relative to glucose itself — the glycaemic index — or by that index scaled to the amount eaten, the glycaemic load. Low-GI foods are typically legumes, whole grains, most vegetables and fruit; high-GI ones are white bread, most potatoes, white rice and sugar. The theory is that slower glucose means less insulin, less hunger and less fat storage; the trials are the test of that theory.
How it works in practice
Whole-grain bread instead of white, oats instead of cornflakes, legumes and vegetables at most meals, fruit rather than juice. In practice the index of a meal is hard to know — fat, protein and fibre in the same meal change it, and cooking and ripeness change it too — so the pattern collapses to a handful of sensible swaps.
What the evidence shows
The Cochrane review of low-GI and low-GL diets for people with overweight or obesity, updated in 2023, pooled ten randomised trials and found little or no difference in weight compared with higher-GI diets, with low-certainty evidence. An earlier version of the same review had been more favourable; the update is a good illustration of why this site dates its reviews. The swaps the pattern recommends are good ones for fibre, satiety and general health — but the mechanism it promises for weight does not survive controlled comparison, and the carbohydrate-and-insulin page explains why.
Who it tends to suit
People who want a simple rule for which carbohydrates without giving them up; people with diabetes or prediabetes, for whom glucose control has value of its own and a doctor's involvement; anyone who was going to eat more legumes and whole grains anyway.
How it most often fails
By trusting the index as a licence — low-GI foods have calories too, and a large bowl of lentils is still a large bowl. And by the tables: applied at the plate to mixed meals, the numbers do not mean much, and the pattern turns into anxiety about pasta.
What to watch
Total energy, as with everything; and the simplification into "whole grain good, white bad", which is roughly right for fibre and roughly irrelevant for weight.
In the app
The glycaemic index is not a policy the app verifies, and the catalogue carries composition rather than GI values; whole grains and legumes among your preferred foods express the pattern within the planner's energy and macro checks.