As we resolve this New Year to slim down our waistlines, perhaps we should consider this – it gets harder to lose weight as we age because our “good” brown fat becomes less efficient at burning the calories stored in our “bad” white fat.

That was the conclusion of a new Japanese study of mice that was published recently. The study also suggests a possible way to reactivate brown fat that could lead to treatments for metabolic diseases.

Brown fat, or brown adipose tissue (BAT), is a “good” fat that we carry at the back of our necks. Although scientists have known for a long time that in newborns, brown fat helps them keep their body temperature stable after birth, not much was known about its function in adults until recently.

Now it appears that brown fat keeps us warm and slim by regulating the metabolism of the white or “bad” fat that we carry around the waist and thighs, where excess calories are stored.

For this latest study, Dr. Junko Sugatani, a researcher in the School of Pharmaceutical Sciences at the University of Shizuoka in Shizuoka, and colleagues, bred and analyzed two groups of mice.

One group of mice was missing a gene for the platelet-activating factor receptor (PAFR), while the other group was normal.

The mice missing the PAFR gene grew fatter with age compared with the normal mice.

The researchers found that the PAFR-deficient mice did not show changes in genes important for metabolism in fat, liver and muscle tissue, and concluded that lack of the PAFR gene causes dysfunction in the thermogenic activity (ability to generate heat) of brown fat which leads to obesity.

They suggest the study sheds light on how the molecular mechanisms involving the PAFR gene might offer a new target for treating obesity and related metabolic disorders, including diabetes, high blood pressure, heart disease, infertility, cancer and ulcers.

Dr Sugatani says:

“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.”

Dr. Gerald Weissmann, the Editor-in-Chief of the FASEB Journal that published the study, says:

“A common complaint is that older people have to work twice as hard with their diets and exercise to get half of the results of younger people.”

He adds:

“Now we have a much better idea why this is the case: Our brown fat stops working as we age. Unfortunately, until a way to turn it back on is developed, we’ll have to be prepared to eat more salads and lean proteins, while logging more miles on the treadmill than our younger counterparts.”

Meanwhile in another study, health behavior researchers found that for some people, retirement-age fitness is linked to having done sport at school.