Rice is a dietary staple for more than half of the world’s population, but scientists still have much to learn about its nutritional makeup. More than 85% of the rice people eat consists of starch. It also contains protein (around 10%), fat (roughly 2%), vitamins, and trace elements. Because lipids make up such a small share of the grain, they have received far less attention than starch, even though they can influence nutrition, flavor, and overall grain quality.
Researchers at Hokkaido University set out to take a closer look at these overlooked fats by studying japonica rice, the short- to medium-grain type commonly associated with Japanese rice. When cooked, japonica rice typically becomes soft, tender, and slightly sticky. It represents about 15% of rice consumption worldwide.
The team examined 56 japonica rice cultivars collected from across Japan, including brown, red, green, and black varieties. The findings were published in Food Research International.
Mapping the Hidden Fats in Rice
“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.”
Modern analytical methods have made it possible to investigate food lipids in far greater detail. Using technologies such as liquid chromatography and mass spectrometry, the researchers carried out a broad analysis of the fats present in japonica rice.
They identified 196 different lipid molecules spanning five major groups.
Black and Green Rice Stand Out
The results also revealed notable differences among rice varieties. Pigmented Japanese rice, especially black and green rice, scored higher on the researchers’ health-promotion index because of their distinctive lipid profiles.
These colorful varieties contained potentially beneficial fats, including compounds called FAHMFAs (fatty acid esters of hydroxy medium-chain fatty acids) and LNAPEs (N-acyl-lysophosphatidylethanolamines). In certain biological systems, these types of lipids have previously been associated with anti-inflammatory activity and improved metabolic health.
The study marks the first time FAHMFAs have been detected in rice.
Testing How Rice Affects Blood Sugar
The researchers also investigated how pigmented rice might influence blood sugar. Rather than testing people directly, they recreated aspects of human digestion in the laboratory.
Selected rice samples were first cooked and then treated with digestive enzymes. The scientists measured how quickly the starch in each sample broke down. That rate can help indicate how rapidly a particular rice variety might raise blood sugar after a meal.
Black and green japonica rice produced a slower rise in blood sugar levels than typical white rice. The results suggest that starch in these varieties is broken down more slowly, allowing glucose to enter the bloodstream more gradually.
That property could make pigmented rice useful in developing foods intended to support heart health, improve blood sugar management, and lower the risk of lifestyle-related conditions such as type 2 diabetes.
Expanding the Search for Bioactive Lipids
The work is part of a wider effort by the research team to identify previously unknown bioactive lipids using advanced analytical techniques.
“Our research group has 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.”
The researchers say the findings could eventually help consumers better understand the nutritional differences among pigmented rice varieties while also encouraging the creation of new health-focused foods.
“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.”