A new study suggests that women who have liposuction to trim their tummies may gain some fat deeper within the abdomen -- a type of fat that's particularly unhealthy.

Brazilian researchers found that within months of abdominal liposuction, there may be an increase in the so-called "visceral" fat that surrounds the abdominal organs.

But the good news, they say, is that regular exercise may prevent that deep fat from forming.

Fat is not "inert tissue," said study leader Fabiana Benatti, of the University of Sao Paulo.

"Removing it by surgery may have important consequences such as the compensatory growth of visceral fat, which may be deleterious in the long term," Benatti told Reuters Health in an email.

Visceral fat is particularly undesirable because it's more closely connected to the risks of type 2 diabetes and heart disease, versus the superficial abdominal fat just under the skin.

The current study, according to Benatti's team, appears to be the first to give "compelling evidence" that visceral fat builds up after liposuction -- at least if you don't exercise.

Exercise deep fat away?

The findings are based on 36 normal-weight women who had liposuction to take away a small amount of superficial tummy fat. All had been sedentary before the procedure.

Benatti's team randomly assigned half of the women to start an exercise program two months after their liposuction. Those women worked out three times a week, walking on a treadmill and doing light strength training, while the rest stuck with their usual lifestyle.

Four months later, the study found, women who'd remained sedentary still had flatter tummies, but were showing a gain in visceral fat -- a 10 percent increase, on average.

In contrast, women who'd been exercising showed no such gain, the researchers report in the Journal of Clinical Endocrinology and Metabolism.

It's not really clear why visceral fat increases post-liposuction, according to Benatti.

"But we believe it may be because this particular fat depot is more metabolically active than the other fat depots," she said.

Another reason, Benatti said, may be because liposuction destroys the "architecture" of fat cells just below the skin. So fat regain may be redirected to still-intact visceral fat cells.

Liposuction no treatment for obesity

In general, experts say that liposuction should not be seen as a substitute for a healthy diet and exercise. And it's intended to reduce stubborn pockets of fat, not as a treatment for obesity, according to the American Society of Plastic Surgeons (ASPS).

In fact, the group says the best candidates for liposuction are people who are normal weight to moderately overweight, and already regularly exercise.

Based on these latest findings, staying active post-liposuction is key, Benatti said.

"If one should choose to undergo liposuction," she said, "it is very important, if not essential, that this person exercises after the surgery."

In the U.S., about 204,700 people underwent liposuction in 2011, according to the ASPS. That was down 42 percent from a decade before.

The known shorter-term risks of liposuction include blood clots, skin or nerve damage, and loose or "rippling" skin where the fat was removed. But little is known about whether liposuction is related to any longer-term health problems, Benatti's team notes.