People who follow a healthy diet and regularly exercise tend to have less abdominal fat, including those deep layers of belly fat that are especially unhealthy, a new study suggests.

Researchers found that among nearly 3,000 middle-aged adults, those who maintained a healthy diet - including lots of fruits, vegetables, whole grains and low-fat dairy - generally had less abdominal fat than those with less-desirable diets.

The same was true of men and women who regularly exercised, as compared with their sedentary counterparts.

Like healthy eaters, exercisers had less abdominal fat just below the skin, as well as less visceral fat - deep layers of fat that surround the abdominal organs and are especially likely to contribute to diseases like diabetes and heart disease.

In contrast, smokers generally had more visceral fat than non-smokers, the researchers report in the journal Diabetes Care.

Many past studies have found that smokers typically weigh less than non-smokers, but these latest findings suggest that smokers may nevertheless have more deep abdominal fat, according to the researchers, led by Dr.

Esther A. Molenaar of the University Medical Center Utrecht, in the Netherlands,

The investigators based their findings on data from 2,926 U.S adults who were 50 years old, on average. Participants completed surveys on their lifestyle habits and underwent CT scans to measure their abdominal fat.

Besides the effects of diet, exercise and smoking, high alcohol intake was related to greater visceral fat in men, though not women.

More studies are needed to see whether there are particular components of a healthy diet, or specific types of exercise, that help reduce visceral fat, according to Molenaar and her colleagues.

As for why smokers tended to have more visceral fat, the reasons are unknown. One possibility, the researchers note, is that smoking encourages deep-fat accumulation because it reduces the action of estrogen and boosts the production of male hormones in both men and women.

SOURCE: Diabetes Care, March 2009.