Brown rice has an average glycemic index of 55, which places it right at the boundary between low GI (55 and under) and medium GI (56 to 69). Depending on the variety and how you cook it, brown rice can fall squarely into the low GI category or creep into medium territory. It consistently scores lower than white rice, which averages around 64 to 73 on the GI scale.
What the Numbers Actually Look Like
The glycemic index ranks foods from 0 to 100 based on how quickly they raise blood sugar. Foods scoring 55 or below are considered low GI, 56 to 69 are medium, and 70 or above are high. A systematic review of rice studies found brown rice averages 55 ± 5, meaning most varieties land between 50 and 60. White rice, by comparison, averages 64 ± 7, with some varieties pushing into the high GI range at 73 or above.
That average of 55 makes brown rice a borderline low GI food. Some specific varieties and cooking methods will keep it solidly low, while others push it into the medium range. The short answer: brown rice is low to medium GI, and meaningfully lower than white rice in every comparison.
Why Variety Matters More Than You’d Expect
Not all brown rice behaves the same way in your body. The key factor is a starch component called amylose. Rice with more amylose digests more slowly, producing a gentler blood sugar curve. Rice with less amylose (and more of its counterpart, amylopectin) breaks down faster and spikes glucose more sharply.
Long-grain varieties like Doongara, which contains up to 30% amylose, tend to score lowest on the GI scale. Whole-grain long-grain rice cooked for just 10 minutes has been measured at a GI of about 44, well within the low range. Basmati rice falls in the middle, with amylose content around 20 to 25%. Short-grain varieties like Koshihikari, popular in Japanese cooking, tend to score higher because they contain more of the rapidly digested starch. Short-grain rice has been measured with a GI around 65 to 84 depending on preparation.
If keeping your GI low is a priority, choosing long-grain brown rice gives you the best starting point.
How the Bran Layer Slows Digestion
Brown rice is simply white rice with its outer bran layer still intact. That bran does two things that affect blood sugar. First, it creates a physical barrier around the starchy interior of each grain, slowing the rate at which digestive enzymes can reach and break down the starch. This means glucose enters your bloodstream more gradually.
Second, the bran is rich in insoluble fiber, which has been consistently linked to improved insulin sensitivity. When this fiber reaches your large intestine, gut bacteria ferment it and produce short-chain fatty acids. These compounds appear to help your body manage blood sugar more effectively over time, beyond just the immediate meal. Brown rice contains nearly all insoluble fiber, the type most strongly associated with reduced diabetes risk.
Cooking Time Changes the Score
How long you cook brown rice significantly affects its GI. Longer cooking promotes greater starch gelatinization, which is a fancy way of saying the starch granules swell, soften, and become much easier for your body to digest quickly. Easier digestion means a faster blood sugar spike.
In one study, whole-grain long-grain rice cooked for 10 minutes had a GI of about 44. Doubling the cooking time to 20 minutes raised the GI to 55, a 25% increase. This is a meaningful jump that can push a low GI rice into medium territory. The practical takeaway: cook brown rice until it’s done, but don’t let it sit simmering longer than necessary. Mushy, overcooked rice will always raise blood sugar faster than rice with a firmer bite.
When studies compare brown and white rice cooked for the same amount of time, brown rice consistently produces lower blood sugar responses. But brown rice needs longer cooking than white rice to become palatable, and when each type is cooked for its own realistic time, the gap between them narrows. The advantage is still there, but it’s smaller than you might assume from the raw GI numbers alone.
The Cooling Trick That Actually Works
Cooking rice and then refrigerating it for about 24 hours before reheating creates something called resistant starch. This is starch that has re-crystallized into a structure your digestive enzymes can’t easily break down, so it passes through more like fiber than like a typical carbohydrate.
The effect is real and measurable. In one study, chilled and reheated rice contained about 12 grams of resistant starch per 100 grams compared to 7.5 grams in freshly cooked rice, a 59% increase. People who ate the cooled-and-reheated rice experienced significantly lower peak blood sugar (9.9 vs. 11 mmol/L) and a dramatically smaller area under the blood sugar curve compared to eating the same rice freshly made. For every 100 grams of chilled rice, roughly 5 fewer grams of carbohydrate are actually digested and absorbed.
This makes meal prepping brown rice a genuinely useful strategy. Cook a batch, refrigerate it, and reheat portions throughout the week. The resistant starch remains even after reheating, so you get the benefit without eating cold rice.
Glycemic Load Gives a Fuller Picture
The glycemic index only tells you how fast a food raises blood sugar, not how much it raises it in a real-world serving. That’s where glycemic load comes in, which factors in how many carbohydrates you’re actually eating. A food can have a moderate GI but still produce a significant blood sugar response if you eat a large portion.
A typical serving of cooked brown rice (about 150 grams, or three-quarters of a cup) contains roughly 33 to 36 grams of carbohydrate. With a GI of 55, that works out to a glycemic load around 18 to 20, which falls in the medium range. Keeping your portion to half a cup drops the glycemic load into the low category. Pairing rice with protein, healthy fat, or vinegar-based dressings also slows digestion and blunts the blood sugar response, effectively lowering the real-world impact regardless of the GI number on paper.
How Brown Rice Compares to Other Grains
- Barley: GI of 25, significantly lower than brown rice and one of the lowest GI grains available.
- Oatmeal: GI of 61, slightly higher than brown rice on average.
- White rice: GI of 64 to 73 depending on variety, consistently higher than brown rice.
If you’re specifically trying to minimize blood sugar impact and rice isn’t essential to the meal, barley is a substantially better option. But within the rice category, brown rice, especially long-grain varieties cooked just until tender and cooled before reheating, offers the lowest glycemic response you can get.