We've all heard that to reduce the risk of heart disease, we need to cut back on saturated fat. But new research is refining that advice, saying replacing that fat with polyunsaturated fats is more important than lowering saturated fat intake alone.

The research found that people who replace saturated fats with polyunsaturated fats -- the kind found in vegetable oils -- have a 19 per cent lower risk of heart disease than those who don't make the switch.

Harvard School of Public Health researchers reviewed eight studies involving more than 13,600 participants. All of the studies were randomized clinical trials in which participants specifically replaced saturated fat in their diet by increasing their consumption of polyunsaturated fat. All the studies also included data on heart disease events, such as heart attacks and stroke.

They found that for every 5 per cent increase in polyunsaturated fat consumption, heart disease risk was reduced by 10 per cent. They also found that the benefits associated with polyunsaturated fat consumption increased with longer duration of the studies.

The study is published online in the journal PLoS Medicine.

For about 60 years, we've been advised to reduce our consumption of saturated fat, which is found mostly in foods from animals, such as meat and dairy. Yet even as many have made such reductions, there has been little scientific evidence that it has resulted in fewer incidence of heart disease.

That's in part because previous studies didn't note what the saturated fat has been replaced with, the authors of this study note.

The researchers note that as the food industry has reduced saturated fat in its products, it's often replaced them with trans fats. (For example, hydrogenated oil has replaced lard in many products.) Yet, a wealth of evidence in recent years has shown trans fat may be just as dangerous, if not more dangerous, than saturated fat.

Surveys also show that while saturated fat has fallen in North American diets, it's generally been replaced with increased consumption of refined flours and sugars.

This study suggests that it's critical to increase the intake of foods high in polyunsaturated fat, such as safflower oil, fatty fish such as salmon and trout, and nuts and seeds such as walnuts and sunflower seeds.

"The specific replacement nutrient for saturated fat may be very important," lead author Dariush Mozaffarian, assistant professor in the department of epidemiology at HSPH said in a statement.

"Our findings suggest that polyunsaturated fats would be a preferred replacement for saturated fats for better heart health."

The Institute of Medicine recommended that 5 to 10 per cent of calories should come from polyunsaturated fats. The results from this study suggest that upper limit may be too low, the study authors contend. They noted that the participants in the studies they reviewed consumed about 15 per cent energy from polyunsaturated fats.