If you have diabetes and want the grain that raises blood sugar least, whole barley wins clearly, with a glycaemic index (GI) of about 28. Rolled oats (about 55) and most millets (from below 55 into the 60s, depending on type) come next, while instant oats, white rice and white bread sit at the high end, above 70.
The ranking only helps if you also watch the portion, the form of the grain and what you eat with it. Here’s how the four compare, using measured values rather than guesses.
What does glycaemic index mean, in plain terms?
GI ranks carbohydrate foods by how fast they raise blood glucose compared with pure glucose (which scores 100). Diabetes UK uses these bands:
- Low GI: 55 or below. Raises blood sugar slowly.
- Medium GI: 56 to 69.
- High GI: 70 or more. Raises blood sugar quickly.
Diabetes UK also makes a point that’s easy to forget: the amount of carbohydrate you eat has a bigger effect on blood sugar than GI alone. A huge bowl of a low-GI grain can still push your numbers up more than a small portion of a medium-GI one.
Oats vs barley vs quinoa vs millets: the numbers
The GI values below come from the international tables of GI values published in Diabetes Care (glucose = 100) and, for millets, a 2021 systematic review and meta-analysis in Frontiers in Nutrition. Carbohydrate, fibre and protein are per 100 g of cooked grain from USDA FoodData Central.
| Grain (as eaten) | GI | GI band | Carbs per 100 g cooked | Fibre per 100 g cooked | Protein per 100 g cooked |
|---|---|---|---|---|---|
| Barley, boiled | 28 | Low | 28.2 g (pearled) | 3.8 g | 2.3 g |
| Rolled oats porridge | 55 | Low | See note below | See note below | See note below |
| Instant oat porridge | 79 | High | – | – | – |
| Millets (average of many types) | 52.7 | Low | 23.7 g (millet) | 1.3 g | 3.5 g |
| Millet porridge (tested as porridge) | 67 | Medium | – | – | – |
| Quinoa | Not in the tables used here | – | 21.3 g | 2.8 g | 4.4 g |
| White rice, boiled (for comparison) | 73 | High | 28.2 g | 0.4 g | 2.7 g |
| Brown rice, boiled | 68 | Medium | – | – | – |
| White wheat bread | 75 | High | – | – | – |
Note on oats: porridge nutrition depends heavily on how much water or milk you use, so a per-100 g cooked figure isn’t very meaningful. Check the dry weight on the pack instead; a typical serving is 40 to 50 g dry.
Two things jump out. First, the same grain can land in different bands depending on how it’s processed: rolled oats are low GI, instant oats are high. Second, white rice and white bread, the default starch for much of the world, are both well above 70.
Barley: the lowest GI grain you can buy
At a GI of 28, barley is in a different league from the others. It’s also rich in beta-glucan, a soluble fibre that turns gel-like in the gut and slows digestion. The US Food and Drug Administration allows a heart health claim for foods providing 3 g or more a day of beta-glucan soluble fibre from whole oats or barley, linked to lower cholesterol, which matters because heart disease is a major long-term risk in diabetes.
How to use it:
- Swap half the rice in a pilaf, risotto or biryani for pearl barley.
- Add a handful to soups and stews (Scotch broth is the classic UK version).
- Cook a batch, cool it and keep it in the fridge for grain salads through the week.
- In India, barley (jau) flour can be mixed into wheat flour for rotis.
The downside is time: barley takes noticeably longer to cook than rice, and hulled barley longer still. A pressure cooker or an overnight soak helps.
Oats: low GI only in the right form
Rolled oats made into porridge scored 55 in the international tables, right on the low-GI line. Instant oat porridge scored 79, which is higher than white bread. The finer the oats are cut and the more they’re pre-cooked, the faster your body breaks them down.
- Best choices: steel-cut (pinhead) oats or old-fashioned rolled oats.
- Use with care: quick oats, instant sachets, and anything labelled “flavoured”, which often has added sugar.
- Make it steadier: add protein and fat. Diabetes UK notes that protein, fat and fibre all slow carbohydrate absorption. Try oats with Greek yoghurt, a spoon of nut butter, chia or flaxseed, or savoury oats with an egg and vegetables.
- Overnight oats made with rolled oats are a handy option if mornings are rushed.
Oats are also a source of beta-glucan, so they count towards that FDA 3 g figure too.
Millets: good on average, but type and cooking matter
The Frontiers in Nutrition meta-analysis pooled data from 39 GI studies across many millet types. It found:
- The average GI of millets was 52.7, about 36% lower than milled rice (71.7) and refined wheat (74.2).
- Low-GI millets (below 55) included foxtail, barnyard, fonio, teff and Job’s tears.
- Medium-GI millets (55 to 69) included pearl millet (bajra), finger millet (ragi), kodo, little millet and sorghum (jowar).
- In people with diabetes, eating millets long term lowered fasting blood sugar by about 12% and after-meal blood sugar by about 15%.
- Minimally processed millets worked better than heavily processed ones.
Note that “millet porridge” tested separately in the international tables came out at 67. Cooking a grain into a soft, wet porridge tends to raise its GI, so a millet upma or pilaf with vegetables is likely to behave better than a thin, smooth porridge.
Millets are everyday food in parts of India and Africa and are easy to find in most supermarkets elsewhere (sorghum and teff are often sold as gluten-free flours). Ragi dosa, jowar or bajra roti, and foxtail millet in place of rice all work well.
Quinoa: the protein pick
Quinoa doesn’t appear in the international tables we used, and we’d rather leave a number out than quote one we couldn’t check. What we can say from USDA data is that 100 g of cooked quinoa has 21.3 g of carbohydrate, 2.8 g of fibre and 4.4 g of protein, compared with 28.2 g of carbs, 0.4 g of fibre and 2.7 g of protein in the same weight of cooked white rice. So, gram for gram, quinoa gives you fewer carbs and more fibre and protein than white rice.
Quinoa is naturally gluten-free and quicker to cook than barley. Rinse it well first to remove the bitter coating. It’s a good base for salads, or a swap for couscous or rice.
Which grain is best for diabetes?
On GI alone: barley, then rolled or steel-cut oats and most millets, then brown rice, with instant oats and white rice last. In real life, the best grain is the one you’ll eat regularly in a sensible portion. A practical rotation might look like this:
- Breakfast: steel-cut or rolled oats with nuts or yoghurt, or a millet dosa with sambar.
- Lunch: a barley and vegetable soup, or a quinoa salad with chickpeas.
- Dinner: foxtail millet or a rice-and-barley mix with dal, fish or chicken and plenty of vegetables.
If you’re trying to bring your numbers down from the prediabetes range, our guide on prediabetes signs and how to reverse it explains the weight and activity targets that matter alongside food choices.
Tips that lower the blood sugar effect of any grain
- Keep portions moderate. The CDC plate method suggests filling one quarter of a 9-inch (23 cm) plate with carb foods. Your dietitian can tailor this.
- Don’t overcook. Grains cooked until soft and mushy are digested faster. Diabetes UK suggests cooking pasta al dente for this reason.
- Add protein, fat and fibre. Beans, lentils, eggs, fish, paneer, tofu, nuts and vegetables all slow the rise.
- Mix grains. Half white rice, half barley or millet is an easy first step for families.
- Check the label. “Multigrain” bread can still be mostly refined wheat. Look for whole grain as the first ingredient.
- Test, don’t guess. If you use a glucose meter or CGM, check your reading 2 hours after a meal with a new grain to see your own response.
For more on how different carbohydrate foods behave, see good carbs vs bad carbs and brown vs white rice.
When to see a doctor or dietitian
Changing your staple grain is safe for most people, but get advice first or soon after if:
- You take insulin or a sulfonylurea (such as gliclazide or glimepiride) and are cutting carbohydrates a lot, because your risk of low blood sugar (hypoglycaemia) goes up.
- You get shaky, sweaty, confused or have readings below 70 mg/dL (3.9 mmol/L) after changing your diet. The CDC defines that as low blood sugar.
- Your readings stay well above the targets your care team set, or you’re losing weight without trying.
- You have coeliac disease (barley contains gluten, and oats are often contaminated with it unless labelled gluten-free) or kidney disease, which can change how much protein and potassium you should have.
- You get bloating or stomach pain after adding a lot of fibre quickly. Increase slowly and drink enough water.
Get emergency help if someone with diabetes is confused, very drowsy, having a seizure or can’t swallow safely. Call your local emergency number (911 in the US, 999 in the UK, 112 in the EU and India).
Frequently asked questions
Is barley better than oats for diabetes?
On GI, yes: boiled barley tested at 28 versus 55 for rolled oat porridge. Both contain beta-glucan, so both are good choices. Oats are easier for breakfast; barley suits lunches and dinners.
Are instant oats bad for people with diabetes?
Instant oat porridge has a GI of 79 in the international tables, which is high. You don’t have to ban it, but steel-cut or rolled oats are a better everyday choice, especially without added sugar.
Which millet has the lowest GI?
In the 2021 meta-analysis, foxtail, barnyard, fonio, teff and Job’s tears were in the low-GI group. Pearl millet, finger millet (ragi), kodo, little millet and sorghum were medium GI on average.
Can I eat quinoa every day if I have diabetes?
Most people can, in sensible portions. It has fewer carbs and more protein and fibre than white rice per 100 g cooked. Count it as your starch for that meal, not an extra.
Is brown rice low GI?
Not quite. Boiled brown rice tested at 68 in the international tables, which is medium GI, compared with 73 for white rice. It still gives you more fibre, but barley, rolled oats and many millets rank lower.
This article is for general information and is not a substitute for advice from a doctor. If you have symptoms or a health condition, please consult a qualified healthcare professional.
