Black and green japonica rice may offer a nutritional edge over white rice, according to Hokkaido University researchers who found the pigmented varieties both raise blood sugar more slowly and contain rare, potentially beneficial fats.

The team analysed 56 japonica cultivars – the short-to-medium-grain type behind most Japanese rice dishes – collected from across Japan, spanning brown, red, green and black varieties. Using mass spectrometry, they mapped 196 distinct fat molecules across five groups, an area of rice’s nutritional makeup that’s been largely overlooked given how little fat the grain contains overall.

Black and green rice stood out, scoring higher on the team’s health-promotion index. Their lipid profiles included FAHMFAs and LNAPEs – compounds tied in earlier research to reduced inflammation and better metabolic health – marking the first time FAHMFAs have been found in rice at all.

“Although lipids make up only a small proportion of rice, they are critical in determining its nutritional value,” said lead author Associate Professor Siddabasave Gowda, noting their role in cell function, energy storage and the body’s signalling processes.

Testing also showed black and green japonica raised blood sugar more gradually than white rice – a trait that could make them useful in foods designed to support metabolic health. The findings are published in Food Research International.