NEW YORK (Reuters Health) - The quality of the food in your diet is more important than the quantity of carbohydrates or fat you're eating in terms of preventing heart disease, Harvard researchers report.

"We should be able to combine the good features of low fat diets and low carbohydrate diets and avoid the bad features of those diets," Dr. Frank Hu of the Harvard School of Public Health in Boston, the study's lead author, told Reuters Health.

"In the past when we recommended low fat, high carbohydrate diets we emphasized reducing fat. We usually don't talk about the quality of carbohydrates," he added.

Carbohydrates are considered poor quality if they are digested rapidly and cause a relatively speedy rise in blood sugar, for example sugared sodas or white bread. Higher quality carbs such as whole grains and vegetables are generally higher in fiber, take longer to digest and produce a slower, steadier blood sugar increase.

As reported in this week's New England Journal of Medicine, Hu and his team originally set out to assess the safety of low-carb diets, which are still popular for weight loss. They analyzed data on nutrition from 82,802 women participating in the Nurses' Health Study over a 20-year period. Information on the participants' diet was gathered every two to four years, so the study was able to capture changes in diet over time.

The percentage of calories a woman got from fats, carbohydrates or proteins had no influence on her heart disease risk, the researchers found. However, women who got more of their calories from healthier sources of protein, such as tofu, beans and whole-grain foods, as well as healthy fats like olive oil, were 30% less likely to develop heart disease over the course of the study.

Also, women who ate diets with the highest glycemic load -- meaning they ate more poor-quality carbs -- had a nearly doubled risk of heart disease.

Based on the findings, Hu advised, "We should definitely reduce the glycemic load of our diet and then use healthy sorts of fats instead of saturated fats and trans-fats and also consume healthy sorts of protein rather than animal protein." While people don't need to avoid animal protein entirely, he added, they should stick to healthier sources like fish and poultry.