Blood Test Warns of Dangerous 'Deep Belly' Fat

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In earlier research, Kahn's team also found that the levels of RBP4 were elevated in people with insulin resistance, people who are obese, and people with type 2 diabetes. This was also the case in healthy people with a family history of diabetes.

According to Kahn, there's ongoing research into drugs that could lower RBP4 levels.

But there's another tried-and-true means of lowering RBP4, she added.

"Levels can also be regulated by physical exercise," Kahn said. In prior research, her team showed that "people who benefited from an exercise program lowered their levels of serum RBP4 when they got more insulin-sensitive," she said.

Kahn had also shown in earlier research that teens who went on a low-carbohydrate diet along with an exercise program lowered their RBP4 levels.

One expert thinks that lowering RBP4 levels might help treat heart disease and type 2 diabetes.

"This study suggests that RBP4 can be a good biomarker to quantify visceral adiposity, which is closely linked to metabolic syndrome," said Dr. Tae-Hwa Chun, from the Department of Internal Medicine, Metabolism, Endocrinology and Diabetes at the University of Michigan. "This article also supports the notion that all the fats are not equal in their functions."

In experiments with mice, RBP4 decreases insulin sensitivity of muscle and liver tissue, which is considered a precursor to diabetes, Chun said.

"It is still not clear whether RBP4 regulates insulin sensitivity by controlling retinoic acid metabolism or by directly acting on muscle or liver cells," Chun said. "The drug Fenretinide, which is shown to lower RBP4 levels, has been already used as a chemotherapeutic agent for cancer. The side effects of the drug, however, need to be carefully weighed against its possible benefit for metabolic diseases."

In another report published in the same issue of the journal, a research team led by Bruce Spiegelman of the Dana-Farber Cancer Institute in Boston identified a gene called PRDM16 that regulates the production of so-called "brown fat" in mice. Brown fat is a type of fat that actually generates heat and counters obesity caused by overeating.