Having junk in your trunk is healthier than a spare tire around the gut, new research suggests. The extra padding on the backside and thighs could even help to protect against disease.
The results come from a review that summarizes various studies on the health effects of different fat stores in the body, particularly around the hips and thighs.
"The fact that body fat's distribution is quite important for your health has been known for some time now," said lead researcher Konstantinos Manolopoulos of the University of Oxford in England. But this new article summarizes a body of research showing that such hip and thigh fat can help to reduce the risk of diabetes and heart disease. The review also suggests a mechanism for conveying those benefits.
The next step is to figure out how our bodies decide where to store fat, say, in the stomach versus the butt. "Once this is understood then one could think about therapeutic approaches to make use of that," Manolopoulos told LiveScience. "Maybe to make use [of it] in a preventive way by redistributing the fat."
Manolopoulos and his colleagues detail their findings this week in the International Journal of Obesity.
Fat not created equal
When looking through the studies, the researchers found that not all fat is created equal.
Stomach fat is considered more metabolically active than lower body fat. While that may sound good, as this fat breaks down easily, the result is a release of substances called cytokines, which have been linked to cardiovascular disease, insulin resistance and diabetes. In fact, research on mice reported in 2008 revealed that belly fat boosts inflammation and is linked with hardening of the arteries – known to increase the risk of heart attacks.
But scientists think lower body fat, like that around the hips and thighs, produces beneficial hormones that protect against these diseases, though more research is needed to firm up this expectation.
In addition, this lower body fat also traps fatty acids. While this long-term storage can make it tricky to slim down your butt and thighs, it's healthier for you if some fat stays put.
"If fatty acids are not stored in fat but are stored in other organs like the liver or the arteries this makes you prone to develop diabetes and heart disease," Manolopoulos said. He added, "One moment on the lips, forever on the hips. It really is exactly this phenomenon; the fat that goes there stays there," on the hips and thighs.
Evidence of healthy butt fat
He says the most compelling evidence for the link comes from population studies showing the more fat individuals have in this hind area the less likely they are to develop diabetes and heart disease later in life.
Other evidence includes instances of Cushing's syndrome, in which patients lose their hip and thigh fat while gaining stomach fat. These patients are known to have an increased risk for diabetes and heart disease.
The scientists aren't sure how the body decides where to store fat, but it's partially genetic.
That genetic force can be seen in the gender differences in how fat gets stored, with women having much more of the healthy, lower body fat than men. And females have a much lower risk for heart disease, Manolopoulos said.
"As long as you are female and your hormones are female hormones you are protected from cardiovascular disease," Manolopoulos said. "The moment you go into menopause and your hormones change, you lose your typical female appearance and you gain stomach fat and at the same time your risk for heart disease and diabetes becomes comparable to men of the same age."
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Jeanna served as editor-in-chief of Live Science. Previously, she was an assistant editor at Scholastic's Science World magazine. Jeanna has an English degree from Salisbury University, a master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a graduate science journalism degree from New York University. She has worked as a biologist in Florida, where she monitored wetlands and did field surveys for endangered species. She also received an ocean sciences journalism fellowship from Woods Hole Oceanographic Institution.