Estimates of obesity in the U.S. range from 30% (Centers for Disease Control data) to 70% (persons selling online and television audience-focused weight-loss programs). We are a nation of fat or fat-obsessed persons, and rightfully so. CDC data shows that the cost of obesity, in 2008 dollars, was estimated at $147 billion. That amount of money would buy a lot of french fries or cheesecake or __ (name your poison).
We all help pay those high-dollar amounts in terms of rising healthcare costs, thus there is considerable interest in finding ways to not only avoid, but also to combat obesity.
In recent years researchers working to understand body fat biology have produced exciting information on differences in types of fat. For instance, we now understand that in addition to white adipose tissue, animals and humans also have brown and beige adipose tissue. White adipose tissue or WAT is commonly found in humans and mice subcutaneously and in visceral fat. Brown adipose tissue or BAT, and beige adipose, is less common, and in humans and mice, is found in deeper cervical, supraclavical and paraspinal areas.
Brown fat or brown adipose tissue (BAT) is metabolically active fat. It contains mitochondria, which contribute the brown color due to their iron content. Much has been learned about brown fat in the past 5-10 years, including that there is more than one type of this adipose tissue.
Not only is there brown, but also beige fat, or as the authors of this work (Schultz T.J., et al.) call it, recruitable brown adipose tissue (rBAT). The authors contrast the two brown fats by noting that constitutive brown adipose tissue (cBAT) is embryonic in origin and is found in the interscapular region of mice. rBAT is found in white adipose tissue (WAT) and in skeletal muscle in mice.
Furthermore, these two brown fats are from different cellular ancestors, cBAT coming from progenitors of skeletal muscle, while rBAT is derived from a non-myogenic lineage.
In May, this writer published a blog on fat research that sounded promising in the battle against obesity and diabetes. That blog focused on research that identified the compound irisin and the ability of irisin to convert metabolically-inactive white adipose tissue to energy-burning brown adipose tissue.
Perhaps indicative of the intensity with which research on brown fat is being pursued, Wu et al. published new information online last week in Cell (July 12, 2012) that there is, in fact yet another type of adipose tissue.
Announcing beige fat. The research is entitled “Beige Adipocytes Are a Distinct Type of Thermogenic Fat Cell in Mouse and Human.”
Brown fat, white fat…isn’t all adipose tissue the same?
Previously thought of as the domain of infants and hibernating bears, brown adipose tissue has been identified in the adult human body as well.
Two papers that appeared in The New England Journal of Medicine in 2009 reported that adult humans have brown fat, found in small blobs. These blobs showed on PET/CT scans when the people scanned were in cool surroundings, with room temperatures at 61–66°F. Blobs of brown fat show up on PET scans because these scans identify areas in the body where cells are more actively using glucose (1–2). Continue reading “The Fat You Wish You Had”