A diet that contains fish oil rich in omega-3 fatty acids may help the body metabolize fat better and thereby gain less weight, according to a study conducted by researchers from the Kao Corporation in Tochigi, Japan, and published in the Journal of Nutrition.

Researchers took mice that had been bred with a predisposition to obesity and fed them a high-fat diet (containing 30 percent of its calories from fat) for five months. Half of the animals had this diet supplemented with 8 percent fish oil.

The mice whose diet had been supplemented with fish oil showed greater activity of several genes related to the metabolism of fats, including carnitine palmitoyltransferase 1a, cytochrome P450 4A10, and malic enzyme.

The supplemented mice also showed greater activity of enzymes related to metabolism. Activity of enzymes related to fatty acid beta-oxidation was 1.2 times higher in the supplemented mice, while the activity of enzymes related to omega-oxidation and malic was 1.6 and 1.7 times higher, respectively.

The results follow a study conducted by researchers from the University of South Australia at Adelaide in May, which found that overweight adults between the ages of 25 and 65 who exercised and received a fish oil supplement each day reduced their fat mass by approximately 1.5 kilograms. In addition, blood triacylglycerol levels decreased by 14 percent, and blood levels of HDL ("good") cholesterol increased by 10 percent.

In the Australian study, participants were given 260 milligrams of docosahexaenoic acid (DHA) and 60 mg or eicosapentaenoic acid (EPA) each day.

A third study, conducted by researchers from the University of Georgia in 2006, found that DHA appeared to decrease fat accumulation and positively influence the programmed death of fat cells.

A number of studies have previously linked omega-3 fatty acids to improved cognitive function and decreased risk of cancer and heart disease.