'Good' Fat Could Fight Obesity

Scientists believe they have identified a 'good' fat tissue that helps burn calories and may lead to new treatments for obesity.

Reporting in three different studies in this week's edition of the New England Journal of Medicine, researchers from Europe and the U.S. say they have identified a fat known as brown adipose tissue in adults and discovered that it plays a role in how the body expends energy.

'At the very least, we have identified that there is an entirely new way of approaching the obesity problem,' said Aaron Cypess, an author of one of the studies and an endocrinologist at Joslin Diabetes Center in Boston.

The brown tissue was thought to be present primarily in young children and generally disappeared with age. Even when the brown fat was found in adults, it was believed to play no role in how the body stores and expends energy.

The advent of high-tech medical imaging, however, has given researchers a new glimpse into the human body that reveals that not only is brown fat present in adults, but that it also is metabolically active. The studies combined images taken with positron-emission tomography, or PET machines, with those from computed tomography, or CT machines, to identify the brown fat.

Brown tissue helps to regulate body temperature by generating heat. In contrast, white adipose tissue stores energy. Obese people have too much of the white tissue.

Francesco Celi, an endocrinologist at the National Institute of Diabetes and Digestive and Kidney Diseases, said the findings may lead to the development of drugs that either help the body produce more of the brown fat or activate existing brown tissue. Treatments likely would take years.

Obesity drugs have proved difficult to develop, and only a few have entered the marketplace. Most focus on curbing appetite or how food is absorbed in the body. Last fall, Merck & Co. scrapped development of its anti-obesity drug taranabant because of side effects.

The findings of Dutch researchers published in the NEJM raise the possibility of nondrug treatments related to brown fat, Dr. Celi said.

The researchers from Maastricht University found that brown tissue can be activated quickly by exposing people to colder temperatures. In their experiment, volunteers were tested after resting on their back for two hours in a room with a temperature of 61 degrees.

'Taken together, these studies point to a potential 'natural' intervention to stimulate energy expenditure: turn down the heat and burn calories,' Dr. Celi wrote in an editorial accompanying the studies. In an interview, he said there is still much research to be done and that the body may compensate for the increase in energy expenditure by triggering a desire to eat more to boost energy intake.

The studies also found that brown fat was more common in women, younger patients and patients who were thin.

Dr. Cypess and colleagues at Joslin are investigating the use of an artificial protein commonly used in spine surgery to stimulate brown tissue. The protein, known as bone morphogenetic protein, or BMP, is used to spur bone growth. Research suggests it also helps create brown fat.

科学家们相信他们发现了一种帮助燃烧卡路里的“有益”脂肪组织，可能会产生治疗肥胖症的新方法。

据本周《新英格兰医学期刊》(New England Journal of Medicine)刊登的三项不同的研究显示，来自欧洲和美国的研究人员表示，他们在成人体内发现了一种被称为褐色脂肪组织的脂肪，对人体能量消耗有着重要作用。

其中一份研究报告的作者、波士顿乔士林糖尿病中心(Joslin Diabetes Center)的内分泌学家塞比斯(Aaron Cypess)说，我们至少发现了一种治疗肥胖的全新方法。

褐色组织此前被认为主要存在于儿童体内，通常会随着年龄增长而消失。即便在成人体内发现褐色脂肪时，这种脂肪也被认为和人体储存与消耗能量没有关系。

不过，高科技医疗成像技术的出现让研究人员对人体有了新的了解：他们不仅在成人体内发现了褐色脂肪，而且还发现这种脂肪的新陈代谢很活跃。研究综合使用了正电子发射断层成象仪(PET)以及断层扫描成象仪(CT)，以识别褐色脂肪。

褐色组织通过生成热量帮助调节体温。相比之下，白色脂肪组织存储能量。肥胖症患者有过多的白色脂肪组织。

美国糖尿病、消化及肾脏疾病研究所(National Institute of Diabetes and Digestive and Kidney Diseases)的内分泌学家切利(Francesco Celi)说，这一发现可能有助于开发相关药物，帮助人体生成更多褐色脂肪，或是激活现有的褐色组织。相关治疗可能要耗时数年。

事实已经证明很难开发减肥药，只有少量药物进入市场。大多数减肥药都专注于控制食欲或是遏制人体对食物的吸收。去年秋天，默克公司(Merck)由于副作用的原因放弃了开发减肥药taranabant。

切利说，荷兰研究人员在《新英格兰医学期刊》公布的这一发现带来了从褐色脂肪着手进行非药物治疗的可能性。

荷兰马斯垂克大学(Maastricht University)的研究人员发现，人置身较低温度下就可以迅速激活褐色脂肪。在实验中，自愿者在一个华氏61度（摄氏16度）的房间里躺了两个小时后进行测试。

切利在研究报告的附加评论中写道，综合来看，这些研究都指向了一种可能的自然干预疗法，即通过降低热量和燃烧卡路里来刺激能量消耗。他在采访中表示，目前仍有很多研究需要做，人体可能会通过提高食欲以增加能量摄入，来弥补能量消耗的增加。

研究还发现，褐色脂肪在女性、年轻病人以及消瘦病人身上更为常见。

乔士林糖尿病中心的塞比斯和同事正在研究一种人造蛋白质的使用，这种蛋白质常用于脊椎外科，用以刺激褐色组织。这种被称为骨形成蛋白(BMP)的人造蛋白质被用于刺激骨骼生长。研究显示，它也有助于生成褐色脂肪。