Understanding Glycaemic Index: A Practical Guide For Everyday Eating

Glycaemic index (GI) ranks carbohydrate-containing foods on a scale of 0 to 100 by how quickly they raise blood glucose after eating, relative to a reference (pure glucose at 100). High-GI foods (≥70) cause rapid rises; low-GI foods (≤55) produce a slower, more sustained response. Glycaemic load (GL) refines this by also accounting for the amount of carbohydrate per serving, which is closer to what actually happens in real meals.

The clinical evidence is strongest in type 2 diabetes management. A Cochrane review and several large meta-analyses show that low-GI dietary patterns can lower HbA1c by around 0.3–0.5 percentage points compared with higher-GI patterns — modest but meaningful, especially when stacked with other interventions. There is also reasonable evidence for benefits in postprandial blood glucose, lipid profiles, and satiety.

In practice, a few simple swaps capture most of the benefit. Choose oats, pulses, basmati rice, sweetcorn, sourdough, and most fruits over instant porridge, quick-cooking white rice, white bread, and many breakfast cereals. Pair carbohydrates with protein, fibre, and healthy fats — that single change blunts the glycaemic response of almost any meal. Cooling cooked starches (rice, potatoes, pasta) overnight increases resistant starch and lowers GI, even after gentle reheating.

Where GI is less useful: as a single rule. A Snickers bar has a moderate GI; that does not make it a good choice. GI also varies between people for the same food, depending on the gut microbiome, time of day, and recent activity. The best plan combines GI awareness with overall diet quality — fibre, micronutrient density, processing level, and portion control.

If you are managing diabetes, PCOS, or reactive hypoglycaemia, working through your typical week with a dietitian is the fastest way to identify the GI swaps that will actually move the dial for you. Generic lists are a starting point — the real value is in the personalised plan that follows.