Margarine and butter have long been debated as to which of them is healthier and now, a new study finds just that.

Previous studies have found the relationship between eating foods rich in saturated fat and developing heart disease, but the new study, published this week in the Journal of the American College of Cardiology, found that what is taken in place of the bad fat can have a significant effect on health.

Foods rich in saturated fat that are replaced with those rich in unsaturated fat, such as plant-based oils and margarine, can significantly lower the risk of heart disease.

For the study, investigators from the Harvard T.H. Chan School of Public Health looked into the diet of thousands of participants.

Researchers provided questionnaires that asked about the participants' details on their lifestyle, diet, medical history, and new diseases for almost 30 years.

Questions included specific food eaten in the past year and the type of oil used for cooking or baking.

What researchers noted in particular is how the participants usually replace the calories consumed from saturated fat with those from refined carbohydrates, such as flour and white bread, instead of consuming unsaturated fats found in plant-based oils, nuts, and carbohydrates like whole grains.

Those who are more into saturated fats tend to have increased risk of heart disease compared to those who cut down on the bad fat.

Conversely, those who go for polyunsaturated fats (those found in vegetable oils) have lowered risk compared to those who ditch these nutrients.

Frank B. Hu, M.D., Ph.D., one of the study authors, said that cardiologists should also take part in their patients' decision to change their lifestyle and diet. They should encourage their patients to eat more healthy carbohydrates and foods rich in unsaturated fats.

The take-home message is not just to lower consumption of bad fat, but also to think about the foods that are being replaced.

Surely, cutting down on foods rich in animal-based fat can protect the heart, but switching to carbohydrate-rich food like pasta, starches, or food from refined flour, is just as bad as eating saturated fats.