A compound in blueberries could help to burn fat, a study has found.

Researchers in Japan have found that a substance in the fruit, pterostilbene, a polyphenol, could cause muscles to lose fat.

In a lab test, researchers exposed the compound to muscle cells from mice.

They found that it caused the cells to start breaking down ectopic fat, a type of fat more common in people who are obese or severely obese that raises the risk of conditions such as type two diabetes and high blood pressure.

Researchers said this happened because the compound triggered a pathway in cells that causes them to begin to break down more fats.

'Our findings establish a scientific framework for developing functional foods and nutritional supplements that target muscle fat metabolism,' Dr Takakazu Mitani, lead study author, said.

'However, beyond the potential of pterostilbene itself, this work provides an experimental framework for identifying other natural compounds [for weight loss].’

Most fat in the body is stored as subcutaneous fat, or under the skin. But people can also build up deposits of ectopic fat, which literally means fat 'in an abnormal place.'

These deposits can build-up in the liver, heart, pancreas and muscles, and raise the risk of multiple complications.

Doctors say those who are obese or severely obese or have larger waistlines are at higher risks, but warn that the fat can also build up in people with flat stomachs. Ectopic fat can only be detected using a detailed body scan.

To reduce these deposits, doctors normally recommend exercise. But scientists are now investigating whether a compound could also help.  

In the study, published in the journal Food Bioscience, researchers at Shinshu University investigated the potential for pterostilbene and four other compounds to clear ectopic fat in muscle cells, or fat stored within the cells.

The other compounds were stilbene, resveratrol, 3-methoxy-resveratrol and 4'-methoxy-resveratrol. Resveratrol is found in grapes, cranberries and others.

In the lab, researchers exposed muscle cells from mice that had ectopic fat deposits to all five compounds for seven days.

They found that pterostilbene triggered them to lose the most fat.

The team said they found that the compound stopped the breakdown of a protein called peroxisome proliferator-activated receptor delta, which is essential for fat breakdown.

By doing this, it led to more of the protein accumulating in the cells, leading to more fat deposits being broken down. 

The scientists said much more research is needed, including in other animals and in humans, to confirm their findings. 

But the research has a similar result to other previous studies in animals which found that pterostilbene could reduce body weight and fat deposits in the liver.

As the study was carried out in cells in the lab, it was not clear what the overall dose was for oral consumption of pterostilbene. But it is likely to be high. 

In a 2014 study where rats lost weight after receiving the compound, the rodents were fed 15 milligrams per kilogram of body weight. That's equivalent to more than 25,000 blueberries per kilogram, or roughly two million blueberries per day for the average adult.