'Good' fat's role in obesity explored
Keeping a healthy weight means balancing how much food you take in with how much energy you put out. Eat too much and the excess is stored as fat. Exercise more and that fat melts away.
But what if fat itself could help burn calories?
New research reported in tomorrow's New England Journal of Medicine adds to growing knowledge about brown fat, the "good" fat that has been studied in mice for its connection to body weight and metabolism.
Babies are born with brown fat deposits that help keep them warm by burning calories instead of storing them, but scientists believed that brown fat disappeared or lay in dormant islands by adulthood. A team led by Dr. Aaron Cypess of the Joslin Diabetes Center has found that brown fat persists in adults and remains active. And in a correlation with potential implications for treating obesity, the researchers found that the more brown fat people had, the lower their body-mass index was, especially in older people.
"There really is a meaningful amount of brown fat in adult human beings and it is functional," Cypess said in an interview. While much remains to be learned, "this now is an entirely new approach to treating obesity."
Cypess and colleagues from Harvard Medical School, Beth Israel Deaconess Medical Center, Brigham and Women's Hospital, and Massachusetts General Hospital looked for brown fat deposits on the PET-CT scans of 1,972 patients. The patients had the whole-body imaging tests to look for cancer or other problems.
The researchers found brown fat with signs of metabolic activity among 106 people, or 7.5 percent of the women and 3.1 percent of the men. People who were over 64 and had a higher body mass index were the least likely to have significant amounts of brown fat. They also examined tissue samples from 33 patients and found a protein involved in generating heat in brown fat.
The authors think the low percentage of people in whom brown fat was detected is likely an underestimate because PET-CT scans would pick up only elevated metabolic activity.
In a link to the heat-generating properties of brown fat, the level of activity rose in cold weather and fell when it was warm, according to weather records for Boston when the patients had their PET-CT scans.
In another article in the Journal, Dutch researchers found that brown fat can be activated by exposing people to cold temperatures. A third study, from Finland and Sweden, also looked at cold and brown fat, finding the same relationship to body mass index.
"These studies, by showing the presence and activity of brown adipose tissue in adult humans, are a powerful proof of concept that this tissue might be used as a target for interventions, pharmacologic and environmental, aimed at modulating energy expenditure," Dr. Francesco Celi of the National Institute of Diabetes and Digestive and Kidney Diseases, writes in an editorial also appearing in the Journal.
Cypess and his co-authors reported having received support from drug and medical device makers. Cypess and two others have pending patent applications related to brown adipose tissue detection, stimulation, or imaging.
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Elizabeth Cooney is a former
health reporter for the Worcester Telegram & Gazette, where she also was a
business reporter and an editor. Earlier in her career, she edited medical
books and journals at Little, Brown, and worked for Boston magazine.Boston Globe Health and Science staff:
- Gideon Gil, Health and Science Editor
- Ishani Ganguli, Short White Coat blogger
