Japanese researchers have solved the long-standing mystery of why people grow fat with age.  Researchers at the University of Shizuoka said that as people age, thermogenic (heat production) activity of brown fat slows down.

The body contains two types of fat - brown and white fat. The white fat is formed around the stomach and thighs as a result of overeating. On the other hand, the brown fat is considered to be a good fat that helps burn bad white fat around the belly.

As the brown fat becomes less efficient (burning less 'bad' white fat), individuals aged 40 and above have to engage in extra amount of physical activity and eat more salads than their younger counterparts in order to lose weight.

"Our brown fat stops working as we age. Unfortunately, until a way to turn it back on is developed, we would have to be prepared to eat more salads and lean proteins, while logging more miles on the treadmill than our younger counterparts," Gerald Weissmann, editor-in-chief of The FASEB Journal, said in a press release.

For the study, the researchers removed platelet-activating factor receptors (PAFR) gene in first group of mice. The second group was left untouched. The researchers discovered that the mice belonging to the first group became overweight with age when compared to the normal group.

 "The research revealed that PAFR-deficiency causes brown adipose tissue (BAT) dysfunction - which converges to induce the development of obesity - due to impaired thermogenic activity of BAT," Junko Sugatani, a researcher at school of pharmaceutical sciences, said.

The researchers also found a potential metabolic on/off switch that could reactivate brown fat. This finding can help develop new/alternative treatments for obesity-related conditions such as diabetes, heart disease, high blood pressure and some cancers.

"Future studies on how PAF/PAFR signaling controls UCP1 levels through beta3-AR production in the BAT of animals and humans may reveal new therapeutic targets to treat metabolic disorders associated with obesity," said Sugatani.

The finding has been published in The FASEB Journal.