Fish oil has been proven to reduce risk of heart disease , stroke, cut blood pressure and cholesterol levels. Now, it may even help burn fat, according to a new study published in the journal Scientific Reports. A long time ago researchers looked under a microscope and discovered two different types of fat in the body — white and brown. Now Japanese researchers from Kyoto University have figured out a possible way to transform fat-storing cells (white) into fat-burning cells (brown).

When a person is born, their body is full of brown fat cells, which convert fat into energy the body can use. Over time, however, the number of brown fat cells decrease, and they’re replaced with white fat cells, which serve as energy reserves in the body (aka excess fat). A recently discovered fat cell, called a beige fat cell, acts a lot like brown fat cells. Without these fat metabolizing cells, fat accumulates in the person’s body as they age. Knowing this, the research team set out to see if certain types of food could increase beige cell counts.

"We knew from previous research that fish oil has tremendous health benefits, including the prevention of fat accumulation," said the study’s senior author Teruo Kawada, a researcher at Kyoto University, in a press release. "We tested whether fish oil and an increase in beige cells could be related."

The team started by feeding two groups of mice high-fat diets. One of these groups, however, had fish oils added into their food. The mice that ate this fish oil-laced food gained 5 to 10 percent less weight and 15 to 25 percent less fat when compared to those that had a regular high-fat diet.  Researchers believe the fish oil was able to decrease body weight and fat accumulation by increasing the number of beige cells, which in turn ramped up oxygen consumption and intestinal temperature, and ultimately led to thermogenesis and calorie burning.  

Fish is a hallmark in the Mediterranean diet, which has been proven to lower risk of heart disease and help people lose weight. But it wasn’t until researchers examined fish oil that they understood the main driver of the dietary benefits. Those who followed a heart-healthy Mediterranean diet were 47 percent less likely to develop heart disease, according to a recent 10-year-long study presented at the American College of Cardiology’s meeting.

"People have long said that food from Japan and the Mediterranean contributes to longevity, but why these cuisines are beneficial was up for debate," Kawada said. "Now we have better insight into why that may be."

Source: Kawada T, Kim M, and Goto T, et al. Fish oil intake induces UCP1 upregulation in brown and white adipose tissue via the sympathetic nervous system. Scientific Reports. 2015.