[Current Opinion Lipidology Feb 2011] Brown fat is greater in hibernating animals due to its activation by an internal antioxidant enzyme called heme oxygenase-1.
Modest biological threats such as radiation and food deprivation activate an internal guardian of genes called heme oxygenase-1 via the Nrf2 gene activator.
Over the past decade when PET scans began to be used to visualize the location, size and growth of tumors by the infusion of radioactive sugar, areas around the neck and collarbone exhibited active metabolic activity and uptake of sugar, evidence of heat and energy expenditure that was identified as brown fat.
The mistaken idea that brown fat is not found in adult humans was erased.
[Current Diabetes Reports April 2010] Brown fat is more commonly detected in women and in younger and leaner individuals.
It is now believed that brown fat can be activated to manage body weight.
[Current Opinion Clinical Nutrition Metabolic Care Jan 2011; American Journal Physiology Endocrinology Metabolism Oct 2010] Brown fat is not only distinguished from white fat by its color but also by its iron content that gives it a tan to dark red color.