Not all fats are created equal, according to recent research at the Harvard School of Public Health.

A study published yesterday in PLoS Medicine and led by Dariush Mozaffarian, an assistant professor of epidemiology at HSPH, showed that replacing saturated fats with a higher than previously recommended percentage of polyunsaturated fats was associated with a significantly decreased risk of coronary heart disease, the leading killer of adults in developing countries.

Poor diet is a risk factor of coronary heart disease, and this study provides quantifiable support for the long-accepted claim that saturated fats in particular can make a person more susceptible to the disease.

According to Mozaffarin, dietary recommendations had been “to reduce total fat intake” because of its link to heart disease.

“Implicitly the message was that all fat is bad and that saturated fat is particularly bad,” he said.

Mozaffarian and his team, which included HSPH researchers Sarah Wallace and Renata Micha, examined the results of several randomized clinical trials of participants who increased their intake of polyunsaturated fats for a year.

Meta-analysis showed participants had a 19 percent reduced risk of coronary heart disease compared to a control group. This means that with each five percent increase in the proportion of calories from polyunsaturated fats, there was a ten percent decrease in coronary heart disease episodes. They also found that a diet made up of 15 percent polyunsaturated fats was more effective at reducing risk than a diet with the previously recommended ten percent.

By encouraging the replacement of saturated fats with polyunsaturated fats and by increasing the percentage of calories that can be allocated to polyunsaturated fats, Mozaffarian said the study’s results are relevant to both industry and individuals.

Mozaffarian said that people often replace fat with carbohydrates. Food producers also frequently substitute saturated fat for trans fat—both of which have detrimental effects.

“The replacement nutrient hasn’t received any attention,” he said.

Mozaffarian said it generally takes ten to twenty years for new research to influence guidelines and for those guidelines to reach public consciousness. Frank B. Hu, a professor of nutrition and epidemiology at HSPH, said this study could begin the “paradigm shift” to focus on “quality of fat” instead of just the quantity.