"Low GI" is one of the more useful ideas in eating with PCOS, and one of the most over-sold. Used well, it is a way of choosing between two kinds of bread. Used badly, it becomes a list of numbers to memorise and a reason to feel you have failed because you ate a potato. This page tries to keep it in its place: what the glycaemic index tells you, what it does not, and the foods that rank low.
It sits under the PCOS diet guide, which explains why insulin is the lever in PCOS. GI is one tool for that lever, not the whole toolbox.
What GI means and what it does not
The glycaemic index, as Diabetes UK defines it, is a ranking from 0 to 100 of how quickly a carbohydrate-containing food makes blood sugar rise after you eat it. A food scoring 55 or below is low GI and raises blood sugar slowly — "slow release" carbohydrate. Between 56 and 69 is medium. 70 or more is high, and raises it quickly.
What it does not tell you is how much carbohydrate you ate. GI is measured on a portion of food containing 50 grams of carbohydrate, eaten on its own, and in real life we eat different amounts in combination with other foods. Diabetes UK's own example: pasta has a lower GI than watermelon, but pasta carries far more carbohydrate, so a similar plateful of pasta moves blood sugar more. The measure that combines GI with the amount of carbohydrate is glycaemic load, and Diabetes UK says plainly that the amount of carbohydrate has a bigger effect on blood sugar than GI alone.
So GI answers "how fast", not "how much". Both matter. Portion size matters more.
Why it matters with insulin resistance
The 2023 international guideline calls insulin resistance a pathophysiological factor in PCOS, and says women with PCOS have an increased risk of impaired glucose tolerance and type 2 diabetes regardless of age or BMI. Food that pushes glucose up fast demands more insulin to bring it down; when the body is already resistant to insulin, that demand is met with more insulin still. Slower carbohydrate asks less of the system. The mechanism is covered in insulin resistance and PCOS.
The evidence for low-GI eating comes mostly from diabetes. Diabetes UK reports that choosing low-GI foods can particularly help manage long-term blood glucose (HbA1c) in people with type 2 diabetes, that it helps keep blood sugar steadier after meals day to day, and that a diet high in fat, high in GI and low in fibre is associated with an increased risk of type 2 diabetes.
One thing to be clear about: the PCOS guideline does not prescribe a low-GI diet. It finds no evidence that any one diet composition beats another for PCOS, and recommends healthy eating tailored to you. Low GI is a way of doing healthy eating — the NHS's advice to choose higher-fibre, wholegrain carbohydrates over white ones lands in the same place — not a separate diet with its own rules.
Low-GI carbohydrates
From the Diabetes UK lists, the foods that rank low (55 or below) include:
- Fruit — strawberries, raspberries, pears, apples, oranges, grapes, dried apricots.
- Vegetables — carrots, tomatoes, spinach, mushrooms, broccoli. Most vegetables are low or medium GI.
- Pulses — beans, peas and lentils of every kind. These are the quiet workhorses of a PCOS plate: carbohydrate, protein and fibre in one ingredient.
- Grains — coarse oatmeal such as steel-cut oats, rye bread, and mixed-grain breads that keep the grains whole.
- Dairy — unsweetened milk and unsweetened yoghurt, low because of their protein and fat.
- Starchy vegetables — yam and plantain.
Medium-GI foods (56 to 69) are still good choices, and include sweet potato, new potatoes, basmati rice, couscous, chapatti, plain popcorn, pineapple, melon and ripe bananas. High-GI foods (70 or more) include white bread and some wholemeal bread, ordinary potatoes however they are cooked, bagels, doughnuts, sweets, sugar-sweetened breakfast cereals and sugary drinks.
Diabetes UK's everyday swaps are the practical version: brown or basmati rice instead of white; granary, pumpernickel or rye bread instead of white or wholemeal; new potatoes with the skin on instead of old floury ones; wholewheat pasta cooked al dente instead of chips; coarse oats or unsweetened muesli instead of sugary cereal; wholemeal chapatti with dhal.
Two things change a food's GI without changing its name. Cooking method, processing and ripeness all shift it — a riper banana ranks higher, and a grain milled to flour ranks higher than the same grain left whole. That is why "wholegrain" and "wholemeal" are not the same: wholemeal bread contains the whole grain but ground up, and can rank as high as white; bread with visible whole grains ranks lower.
Protein and fat slow the rise
GI values describe a food eaten alone, and almost nobody eats bread alone. Diabetes UK explains that protein, fat and fibre all slow the digestion and absorption of carbohydrate, so combining foods changes the GI of the meal. Fibre acts as a physical barrier. Fat lowers GI — which is why chocolate has a low GI and crisps rank below plain boiled potato. Protein lowers it too, which is why milk and yoghurt rank low.
This is the most useful fact on the page, because it turns a list of forbidden foods into a way of building a plate. A potato on its own is high GI; a potato with fish and vegetables is a different meal. Toast on its own is high GI; toast with eggs is not the same event. The habit the PCOS diet guide recommends — build each plate around protein, vegetables and a slower carbohydrate, rather than eating carbohydrate on its own — is the practical application. The 7-day PCOS meal plan is that habit written out for a week.
Diabetes UK adds a caution that follows from the same fact: not every low-GI food is a healthy one. Chocolate ranks low because of its fat, not because it is good for you.
Reading a label
GI is not printed on food labels, and the NHS and Diabetes UK both point you to what is. The NHS gives the sugar thresholds: more than 22.5 grams of total sugars per 100 grams means a food is high in sugar, and 5 grams or less per 100 grams means it is low. For the "slow release" question, look for fibre — Diabetes UK says wholegrains and high-fibre foods slow carbohydrate absorption — and for whether the grain is whole or milled, which the ingredients list shows and the front of the pack often does not. A "wholemeal" loaf and a "wholegrain" loaf can carry the same wholesome-looking words and behave differently.
In the app: scan a barcode and PCOS Pal gives the food a score built from its protein and carbohydrate share and, where the value is known, its glycaemic index. It is a quick comparison between two packets, not a verdict on a food.
Limits of GI
Diabetes UK asks the question directly — is it OK to focus only on GI? — and answers no. A diet chosen on GI alone can end up high in fat and calories and unbalanced. GI is one aspect of a healthy diet, alongside protein, fat, fibre, and the balance of the plate: low in saturated fat, salt and free sugars, with fruit, vegetables, wholegrains, pulses, nuts, fish and unsweetened dairy. Diabetes UK's summary is that the most important thing is to watch carbohydrate portion sizes and spread carbohydrate evenly across the day; choosing low-GI options on top of that is a bonus.
For PCOS, that fits the guideline exactly. There is no low-GI diet to follow. There is a way of eating that keeps blood sugar steadier, and this list is one of the ways to get there.
Sources
- Diabetes UK — Glycaemic index and diabetes
- Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of PCOS (Human Reproduction, full text at PMC)
- NHS — 8 tips for healthy eating
This article is for education. It is not medical advice, diagnosis or treatment — talk to a clinician about your own care.
More in this series
- PCOS diet: what to eat, and why it works — What the evidence says about eating with PCOS: insulin, the pattern that helps, the foods worth limiting, and why no rigid plan is required.
- Anti-inflammatory eating for PCOS: what is real — Where "anti-inflammatory" and PCOS actually meet, which foods the evidence supports, which only marketing does, and how it overlaps with insulin advice.
- Foods to limit with PCOS, and why banning them backfires — The foods worth eating less often with PCOS, the evidence for each, and why "limit" beats "never" for a diet you can keep.
- Insulin resistance and PCOS, explained — What insulin resistance is, why it is so common in PCOS, how it is actually tested, and what food, movement, sleep and medication each do about it.
- PCOS breakfast ideas that hold you until lunch — Why breakfast is where PCOS eating plans break, the protein-fibre-fat template that fixes it, ten breakfasts that use it, and what to do about coffee.
- A 7-day PCOS meal plan you can actually keep — Seven days of ordinary meals built on the pattern the evidence supports, with a shopping list and swaps, and no food group cut out.