The rice on your plate may affect blood sugar differently than you think — scientists find black and green varieties contain unusual fats and slower-digesting starch

Rice is usually judged by its carbohydrate content. But researchers in Japan have found that the grain contains a much wider range of fats than commonly discussed, and some varieties may take longer to break down during digestion.

A study from Hokkaido University has identified 196 lipid molecules in Japanese rice, including a group of compounds never previously detected in rice. Black and green varieties stood out for their distinctive fat profiles and slower starch breakdown in laboratory experiments.

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The findings add to growing scientific interest in how different rice varieties may influence nutrition. They also raise a question relevant to anyone who eats rice regularly: does the type of grain matter as much as the amount?

The researchers examined 56 japonica rice cultivars collected from across Japan. Their findings were published in Food Research International.

The overlooked fats inside a grain of rice

Rice contains mostly starch, which explains why so much nutrition research has focused on its carbohydrates. Fat accounts for only around 2% of the grain, compared with roughly 10% protein and more than 85% starch.

That small fat fraction, however, is chemically diverse.

Lipids play roles in cell membranes, energy storage and biological signalling. They can also influence the nutritional properties and quality of food. Yet the full range of fats in rice has not been studied as extensively as its starch.

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The Hokkaido University team set out to examine that neglected part of the grain.

Their research focused on japonica rice, the short- to medium-grain variety commonly used in Japanese cooking. Once cooked, it tends to be soft and slightly sticky. Japonica accounts for about 15% of rice consumption worldwide.

The 56 cultivars in the study included brown, red, green and black rice. By comparing their chemical profiles, the scientists looked for differences that might explain why some varieties behave differently from others.

The analysis revealed a surprisingly broad collection of lipids.

Black and green rice contain distinctive compounds

The researchers identified 196 lipid molecules belonging to five major groups.

Pigmented rice, particularly black and green varieties, showed distinctive lipid profiles and higher scores on the study's health-promotion index.

Two groups of compounds drew particular attention: FAHMFAs, or fatty acid esters of hydroxy medium-chain fatty acids, and LNAPEs, also known as N-acyl-lysophosphatidylethanolamines.

Some lipids in these categories have been associated with biological processes involving inflammation and metabolic health. That does not mean the compounds automatically produce those effects when consumed in rice. Their activity, absorption and significance in the human body still need to be established.

The study's most unusual chemical finding was the detection of FAHMFAs in rice for the first time.

Associate Professor Siddabasave Gowda, the lead author, said the research group wanted to better understand the nutritional role of rice lipids, which have received less attention than starch.

The discovery gives scientists another way to distinguish between rice cultivars. Two grains that look different on the outside may also differ in the molecules they contain.

Why slower starch digestion matters for blood sugar

The fat findings were only part of the investigation. The researchers also tested how quickly starch from selected rice samples broke down under laboratory digestion conditions.

The process was straightforward: the rice was cooked, treated with digestive enzymes and analysed to measure starch breakdown.

Black and green japonica rice showed slower starch digestion than typical white rice in these experiments.

That difference matters because starch must be broken down into smaller sugars before glucose can be absorbed. The rate of digestion can influence how quickly glucose becomes available after eating.

A slower breakdown rate may therefore be relevant to foods designed to produce a more gradual release of carbohydrates.

But the experiment did not measure blood sugar in people. It also did not establish that black or green rice prevents diabetes, lowers long-term glucose levels or improves insulin sensitivity.

The researchers have identified a possible difference in digestion, not a proven dietary treatment.

Cooking method, serving size, the rest of a meal and individual metabolism can all affect the blood sugar response to rice. Those factors were not enough to be resolved by this laboratory study.

What the findings could mean for future rice products

The work is part of Hokkaido University's wider research into bioactive lipids in Japanese foods.

Gowda's group has also investigated unusual fats in dietary fish, herbal teas and seaweeds. The broader aim is to identify compounds that may have useful biological properties and understand where they occur in food.

The rice study adds pigmented grains to that research.

It could help scientists investigate whether particular cultivars have nutritional characteristics worth preserving or using in new food products. It may also encourage more detailed comparisons between rice varieties that are often grouped together simply as white, brown or coloured rice.

The researchers hope their findings will support the development of functional rice products for people concerned about diabetes and other lifestyle-related diseases.

That goal remains a future possibility.

Before any health claim can be made, scientists would need to determine whether the unusual lipids are absorbed in the body, whether they have measurable effects and whether the slower starch breakdown seen in the laboratory produces a different glucose response in humans.

For people choosing rice today, the study provides useful information about the grain's chemistry, but not a reason to treat one variety as a proven solution for blood sugar control.

The next step is to find out whether the differences observed in a laboratory also matter after the rice is eaten.

Frequently asked questions

1. Does black rice raise blood sugar more slowly than white rice?

The study found slower starch breakdown in black rice than in typical white rice during laboratory digestion tests. It did not directly measure blood sugar responses in humans.

2. What unusual fats were found in black and green rice?

The researchers identified compounds called FAHMFAs and LNAPEs. FAHMFAs were detected in rice for the first time in this study.

3. Is green rice good for people with diabetes?

The research does not establish that green rice improves diabetes or prevents the disease. Human studies would be needed to determine its effect on blood sugar.

4. How many rice varieties did the scientists study?

The team examined 56 japonica rice cultivars from across Japan, including brown, red, green and black varieties.