Japanese Pigmented Rice Contains Unique Beneficial Fats

Study of 56 japonica rice varieties finds black and green rice to be healthier choices

Rice feeds more than half of the world's population, yet we still only partly understand the nutrients it contains. More than 85% of the rice we eat is composed of starch, though it also contains some protein (around 10%), small amounts of fat (roughly 2%), a few vitamins, and trace elements. Because fats, or lipids, make up such a small fraction of rice, they have received relatively little scientific attention, despite playing an important role in nutrition, flavor, and grain quality.

To address this gap, researchers at Hokkaido University studied japonica rice varieties, which are short- to medium-grain rice most familiar as Japanese rice. They become soft, tender, and slightly sticky when cooked, and account for roughly 15% of global rice consumption. The researchers collected and analyzed 56 japonica rice cultivars from across Japan, including brown, red, green, and black varieties. Their findings were published in the journal Food Research International in January 2026.

"Although lipids make up only a small proportion of rice, they are critical in determining its nutritional value," explains lead author Associate Professor Siddabasave Gowda. "They help maintain cell membrane integrity, store energy, and support essential signaling processes in the body."

Thanks to advances in analytical technologies, such as liquid chromatography and mass spectrometry, scientists can now study dietary lipids in food in far greater detail than before. Using these tools, they identified 196 different types of lipid molecules belonging to five major groups in a comprehensive analysis of japonica rice varieties.

The team also discovered that colorful Japanese rice varieties, particularly black and green rice, have a higher health-promotion index given their unique lipid composition. They contain potentially beneficial fats, including compounds known as FAHMFAs (fatty acid esters of hydroxy medium-chain fatty acids) and LNAPEs (N-acyl-lysophosphatidylethanolamines). These lipids were linked to anti-inflammatory effects and improved metabolic health in certain biological systems previously. This is the first time FAHMFAs have been identified in rice.

The researchers also studied how these pigmented rice varieties affect blood sugar. They did this by simulating human digestion in the laboratory. Selected rice samples were cooked and then exposed to digestive enzymes to measure how quickly their starches broke down, an indicator of how sharply each type of rice could raise a person's blood sugar level after a meal.

Black and green japonica rice produced a slower rise in blood sugar levels compared with typical white rice. This suggests that they contain starch that is digested more slowly and released into the bloodstream more gradually. As a result, these pigmented rice varieties could be used to make food products that will support heart health, manage blood sugar, and reduce the risk of lifestyle-related conditions such as type 2 diabetes.

This study builds on the researchers' broader efforts to characterize previously unknown bioactive lipids using advanced analytical techniques. "Our research group has previously discovered novel bioactive lipids in Japanese dietary fish, herbal teas, and seaweeds," Gowda adds, "helping to shed light on Japan's underexplored lipid-rich food resources."

"People may be interested in learning about the health benefits of different pigmented rice varieties and based on this knowledge, choosing the type that best suits their needs," says Gowda. "We also hope our findings will support the development of new 'functional' rice products to better manage diabetes and other lifestyle-related diseases."

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This study was supported by the Japanese Society for the Promotion of Science Grants (25K00258) and JST SPRING (Grant Number JPMJSP2119).