As many of you might remember from your animal development lessons, mammals are born with brown fat, a type of fat that stores energy and releases that energy as heat–which is very handy in creating body heat for critters that cannot generate heat by shivering. So cool (or hot, as the case may be)! As mammals get older, brown fat is greatly reduced unless they are hibernating mammals. Mammals are then sidled with white fat, which many of us have come to know as love handles and muffin tops and in most cases just adds to our growing overweight and obesity epidemic.
Published today in The Scientist and in Cell, researchers Dodd et.al. in Australia have demonstrated a strong, if not causative relationship, between the conversion of white fat to brown fat through the hormones leptin and insulin. These hormones have long been associated with metabolism, hunger and satiety and weight, but until now were not understood in this mechanism. Here is how it works: appetite suppressing neurons in the hypothalamus receive information from blood-borne leptin and insulin, telling the rest of the body, including fat tissue, that “we’re satisfied.” In the lab, mouse models were designed such that genes were disabled for two phosphatase enzymes that dim the responsiveness of these hypothalamic neurons to leptin and insulin. These mice converted white to brown fat and did not gain weight when fed a high-fat diet, unlike mice without the double gene knockout.
It will be interesting to study this mechanism in people, though we can’t use the same study design–genetic engineering isn’t possible in this way with humans. That being said, I just might sign up for a Phase II trial on this work. I’d be very enthusiastic about having more brown fat and less white fat!
Best regards and happy browning,