WEDNESDAY, Nov. 16 (HealthDay News) -- A new study offers further evidence that a Mediterranean-style diet is good for your heart.

The research found that unsaturated fats from foods such as avocados, olive oil and nuts increase the body's ability to use insulin. Reduced insulin action can lead to diabetes, which is a risk factor for heart disease.

Researchers examined how three different types of balanced diets consumed by 164 people with mild hypertension but no diabetes affected the body's ability to maintain healthy insulin levels and regulate blood sugar levels. The three diets were rich in either carbohydrates, protein or unsaturated fats such as those found in olive oil.

The participants ate each of the three diets for six weeks in a row, with two to four weeks off in between each diet. Blood samples were used to monitor insulin and glucose levels.

The diet rich in unsaturated fats improved insulin use significantly more than the high-carbohydrate diet, which featured refined carbohydrates such as pasta and white bread.

This beneficial effect of the unsaturated fat diet occurred even though the participants did not lose weight.

"A lot of studies have looked at how the body becomes better at using insulin when you lose weight," Dr. Meghana Gadgil, a postdoctoral fellow in the division of general internal medicine at the Johns Hopkins University School of Medicine, said in a Hopkins news release. "We kept the weight stable so we could isolate the effects of the macronutrients. What we found is that you can begin to see a beneficial impact on heart health even before weight loss."

The researchers said their findings show that dietary changes can improve heart health in those at risk for cardiovascular disease, even if they don't lose weight.

"The introduction of the right kind of fat into a healthy diet is another tool to reduce the risk of future heart disease," Gadgil said.

The study was to be presented Wednesday during the American Heart Association's annual meeting in Orlando, Fla. Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

The American Heart Association has more about a Mediterranean diet.