It's no secret that stress isn't good for you. But what's less clear is how social stressors like a high-pressure job or a failing marriage affect your physical well-being.

Researchers at Wake Forest University who study stress in monkeys think they may have discovered a clue: fat. More specifically, the particular form of fat called visceral fat that tends to build up in the abdomen （those dreaded beer bellies and love handles）. Researchers believe this abdominal fat lodges deep within visceral organs, such as the heart, liver and blood vessels, and may be an indicator of increased heart attack risk. In a study of 42 female monkeys, the scientists found that those with the most social stress - in the monkeys' case, that meant being at the bottom of the social hierarchy - packed away the most fat around the middle.

"For years now there has been a recognition that the pattern in which people lay down fat is associated more with health than the absolute amount of fat," says study co-author Carol Shively, a pathologist at Wake Forest. "Fat cells that live in the visceral depot behave differently than cells that live in other areas of the body."

Recent evidence suggests that visceral fat cells are active, unlike the fat cells found elsewhere in the body just under the skin, known as subcutaneous fat. Those fat cells are essentially just storage sinks for calories. But visceral fat cells actively secrete hormones and other agents that affect the metabolism of sugar and the way the body burns calories. In people, visceral fat has been linked to metabolic changes, such as higher blood pressure and blood sugar levels, that increase risk for diabetes and heart disease.

Shively and her colleagues also knew that people who produce excessive amounts of the stress hormone cortisol tend to have bulky waistlines; they have apple-shaped bodies, rather than pear-shaped. So the researchers wanted to examine all these factors - stress, abdominal fat and health risk - in one study. The problem, of course, is that measuring the relationship between stress and visceral fat in people in a controlled fashion isn't easy. So, the team turned to monkeys. For nearly two and a half years, she and her team fed the animals a typical Western diet, with 40% of calories coming from fat, measured their cortisol levels and used CT scans to calculate the amount of visceral fat each monkey carried.

The monkeys were housed in groups of four, automatically prompting them to establish a linear hierarchy of dominance. The dominant monkey in each group experienced the least stress, according to researchers. "They were groomed more than the subordinates, and they would get relaxed. Their eyes would roll up, sort of like they were getting a massage," says Shively. Monkeys further down the power chain, however, appeared more stressed-out. They were more vigilant, constantly scanning their environment for potentially aggressive threats from the leader. They also spent more time alone, out of contact with the other monkeys.

CT scans showed that group leaders and the second most dominant monkeys showed lower amounts of visceral fat than their subordinates, who carried the bulk of their body fat in their guts. In human populations, something similar happens: Studies have linked lower social status to a higher incidence of metabolic syndrome - the condition whose symptoms include being overweight and having high blood pressure and high glucose levels - which promotes heart disease.

Together with Shively's findings, says Dr. David Katz, director and co-founder of the Yale Prevention Research Center, the human data suggests a possible cause-and-effect link: Stress may promote accumulation of visceral fat, which in turn causes metabolic changes in the body that contribute to heart disease and other health problems.

"This study shows that psychological stress, which we know can affect stress hormone levels, can have a fairly rapid influence on where extra calories go," he says. "I'm generally quite cautious about animal research but here I think we're seeing something that has direct relevance to human health as well."

众所周知，压力不是件好事。但是，社会压力如何影响身体健康，比如工作压力大，婚姻失败等，就不太清楚了。

Wake Forest大学的猴子研究人员认为，他们可能找到了一条线索：脂肪。更具体的说是，一种特定的往往在腹部堆积的内脏脂肪（导致那些可怕的啤酒肚和游泳圈）.研究人员认为，这种腹部脂肪蓄积在内脏器官的深处，比如心、肝、血管等，可能表明心脏病的几率更大。通过研究42只母猴，科学家们发现那些社会压力最大的猴子，即最底层的猴子，腹部脂肪最多。

研究的合伙作者Carol Shively是Wake Forest的一名病理学家。他说："多年来，人们认识到脂肪增加的模式和健康的关联，大于和绝对脂肪量的关系。""内脏器官中的脂肪细胞在不同的身体里活动也不一样。"

最近的发现表明，内脏脂肪细胞是活性的，不同于身体中其他部位的皮肤下面的脂肪细胞，也就是皮下脂肪。这些皮下脂肪细胞只是存储卡路里的容器。但是活性的内脏脂肪细胞分泌影响糖代谢和身体燃烧热量的激素和其他因素。就人类而言，内脏脂肪和新成代谢的变化有关，如血压血糖增加，进而增加了糖尿病和心脏病的风险。

Shively及其同事都知道，分泌过多的压力荷尔蒙皮质醇的人往往大腹便便，身材更像苹果，而不是梨子。因此，研究人员希望检查以下因素，例如压力、腹部脂肪和健康风险，并将结果集中到一份研究里。当然，问题在于用控制的方式测算压力和内脏脂肪的关系并非易事。所以，他们用了猴子。近两年半的时间里，Shively和她的团队让猴子们吃典型的西餐，其中四成热量来自脂肪。他们测算猴子的皮质醇水平，利用CT扫描，计算每只猴子体内的内脏脂肪数量。

猴子们四只一组，可以促使他们自发的形成上下等级关系。研究人员说，每组中占据统治地位的猴子压力最小。Shively说，"上级的猴子被梳理毛发的次数超过下属，他们可以很放松，眼睛上翻，就像接受按摩一样。"但是那些越底层的猴子似乎压力越大。他们更警觉，常常左顾右盼，防止来自首领的潜在威胁。他们独处的时间也更多，不和其他猴子交流。

CT扫描的结果表明，首领们和次级首领猴子的内脏脂肪低于他们的下属，下属们都拖着肥肥的肚子。在人类的世界里，情况有些类似。研究发现社会地位低往往导致代谢问题的发病率更高，例如超重，高血压和高血糖，这些都会导致心脏病。

除了Shively的发现，耶鲁预防研究中心的主任兼合伙创办人，David Katz说，人类的实验数据中存在一种可能的因果关系。压力可能会促进内脏脂肪的堆积，进而导致代谢变化，引发心脏病和其他健康问题。

他说，"我们都知道心理压力影响压力荷尔蒙的水平，而这份研究表明心理压力也会迅速影响额外热量的走向。""对于动物的研究，我一般都很谨慎。但是，我想这份研究显示出某种直接影响人类健康的因素。"