CHICAGO - Here's a health tip in a nutshell: Eating a handful of nuts a day for a year - along with a Mediterranean diet rich in fruit, vegetables and fish - may help undo a collection of risk factors for heart disease.

Spanish researchers found that adding nuts worked better than boosting the olive oil in a typical Mediterranean diet. Both regimens cut the heart risks known as metabolic syndrome in more people than a low-fat diet did.

"What's most surprising is they found substantial metabolic benefits in the absence of calorie reduction or weight loss," said JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital.

In the study, appearing yesterday in the Archives of Internal Medicine, the people who improved most were told to eat about three whole walnuts, seven or eight whole hazelnuts, and seven or eight whole almonds. They did not lose weight, on average, but more of them succeeded in reducing belly fat and improving their cholesterol and blood pressure.

Manson, who was not involved in the study, cautioned that adding nuts to a Western diet - one packed with too many calories and junk food - could lead to weight gain and more health risks.

"But using nuts to replace a snack of chips or crackers is a very favorable change to make in your diet," Manson said.

The American Heart Association says 50 million Americans have metabolic syndrome, a combination of health risks, such as high blood pressure and abdominal obesity. Finding a way to reverse it with a diet people find easy and satisfying would mean huge health improvements for many Americans, Manson said.

Nuts help people feel full while also increasing the body's ability to burn fat, said lead author Jordi Salas-Salvado of the University of Rovira i Virgili in Reus, Spain.

More than 1,200 Spaniards, ranging in age from 55 to 80, were randomly assigned to follow one of three diets. They were followed for a year. The participants had no prior history of heart disease, but some had risk factors including Type 2 diabetes, high blood pressure and abdominal obesity.

At the start, 751 people had metabolic syndrome, about 61 percent, distributed evenly among the three groups.

The low-fat group was given basic advice about reducing all fat in their diets. Another group ate a Mediterranean diet with extra nuts. The third group ate a Mediterranean diet and was told to make sure they ate more than four tablespoons of olive oil a day.

After one year, all three groups had fewer people with metabolic syndrome, but the group eating nuts led the improvement, now with 52 percent having those heart risk factors. In the olive-oil group, 57 percent had the syndrome.

In the low-fat group, there was very little difference after a year in the percentage of people with the syndrome.