There is a reason why people with more stored fat find it difficult to lose weight compared to others. In a joint study, scientists from the University of Cambridge in the U.K. and Toho University in Japan explain that certain fat cells produce a protein that inhibits weight loss.

The process of burning energy to produce heat, called thermogenesis, occurs in fat cells known as brown adipocytes. However, the researchers found that fat cells produce a protein called sLR11, which inhibits thermogenesis and prevents the body from losing weight.

What's more, they found that the more fat cells a person has, the more amount of sLR11 protein gets produced in that person's body. In other words, the fatter a person is, the more that person's body resists burning calories.

"Our discovery may help explain why overweight individuals find it incredibly hard to lose weight. Their stored fat is actively fighting against their efforts to burn it off at the molecular level," study author Andrew Whittle said in a press release.

In a study involving mice, the researchers discovered that sLR11 binds to fat cell receptors to prevent the activation of thermogenesis. In a way, this protein signals the body to store fat more efficiently, thus preventing weight loss.

"We have found an important mechanism that could be targeted not just to help increase people's ability to burn fat, but also help people with conditions where saving energy is important such as anorexia nervosa," lead researcher Toni Vidal-Puig said.

The study was published online Nov. 20 in the journal Nature Communications.