Eating whole grains instead of refined grains may have benefits for your waistline, a new study suggests.

Adults who ate three or more servings of whole grains per day, and limited their refined grains to less than one serving per day, had 10 percent less belly fat than those who did not follow this diet, study researcher Nicola McKeown, a scientist with the USDA Human Nutrition Researcher Center on Aging at Tufts University, said in a statement.

For comparison, a slice of 100 percent whole wheat bread or a half-cup of oatmeal constitutes one serving of whole grains, and a slice of white bread or a half-cup of white rice represents a serving of refined grains, she said.

The findings held true even after the researchers accounted for other facts that may have influenced the results, such as the participants' smoking, alcohol intake, fruit and vegetable intake, percentage of calories from fat and physical activity.

The study involved 2,834 men and women, ages 32 to 83, who filled out questionnaires about their diet. The participants also underwent body scans to determine their fat distribution — researchers measured how much fat was around the belly, so-called visceral fat, and how much was found in other parts of the body under the skin, known as subcutaneous fat.

Visceral fat is thought to be worse for you than subcutaneous fat. Previous work has linked belly fat with the development of metabolic syndrome, a cluster of symptoms including hypertension, unhealthy cholesterol levels and insulin resistance, which can develop into cardiovascular disease or Type 2 diabetes.

However, eating lots of whole grains didn't have the same benefits if people also consumed a lot of refined grains as well. Those who ate more than four servings of refined grains per day did not show improvements in their visceral fat volumes even if they also consumed whole grains, McKeown said.

"This result implies that it is important to make substitutions in the diet, rather than simply adding whole grain foods. For example, choosing to cook with brown rice instead of white, or making a sandwich with whole-grain bread instead of white bread," McKeown said.

The researchers noted the study only shows an association, and future work in a larger, more diverse population will be needed to confirm the findings.

This study was funded by the National Heart Lung and Blood Institute, the USDA and a research grant from the General Mills Bell Institute of Health and Nutrition.

The results were published in the November issue of The American Journal of Clinical Nutrition.