Researchers gain some insight into why some fat is good and other fat is bad

Doctors know that excessive upper body fat can increase insulin resistance, potentially leading to diabetes and metabolic disease. They also have shown that lower-body fat, in the thighs for example, seems to protect against such illnesses.

Now a team at the Mayo Clinic has possibly shown why: Abdominal fat cells grow in size, while lower body fat cells grow in number.

The difference in the way the two types of cells grow may influence their effects on the body, said Dr. Michael Jensen, the lead author of the study appearing online Monday in the Proceedings of the National Academy of Sciences. “Different mechanism, different impact,” he said in a statement.

The team recruited 28 extremely lucky test subjects to systematically overeat for eight weeks. The group -- 15 men and 13 women, all normal weight and all 27 to 31 years old -- gorged themselves on “giant candy bars, ice cream shakes, high-calorie drinks and almost anything else they wanted to eat,” according to a Mayo Clinic news release. On average, they gained 5.5 pounds of upper body fat and 3.3 pounds of lower-body fat.

The scientists found that gaining that much lower-body fat resulted in the creation of 2.6 billion new fat cells, challenging the notion that the number of fat cells remains constant in adults once they’ve hit age 20. The paper suggests that the ability to store fat through the creation of cells in the lower body staves off the expansion of cells in the upper body -- the kind of fat gain that promotes disease.

The research did not indicate if test subjects were happier after two freewheeling months of eating chocolate.

--Eryn Brown / Los Angeles Times