By Cari Nierenberg, Contributing writer
Published: 03/19/2014 08:33 AM EDT on LiveScience
Eating more of the "good" kinds of fat and less saturated fat may not be the best way to reduce the risk of heart disease, a new review suggests.
Researchers did not find a strong link that people who ate lots of the good (polyunsaturated) fats found in vegetable oils, and low amounts of saturated fats found in foods such as butter and pork, had a reduced risk of heart disease.
The researchers concluded their analysis "did not yield clearly supportive evidence for current cardiovascular guidelines" and that diet advice based on them "may require reappraisal." [Infographic: The 3 Types of Fats Explained]
However, the results did show a link between eating more trans fats, which are the partially hydrogenated oils added to foods to keep them fresh longer, and an increased risk of heart disease. In other words, the advice that people should avoid trans fats is still good advice.
The new study was a meta-analysis of 72 previous studies involving more than 600,000 people in 18 countries.
"Our report was an attempt to do the most comprehensive assessment of fatty acids by combining data from all previous studies into a single investigation," said study author Dr. Rajiv Chowdhury, a cardiovascular epidemiologist at the University of Cambridge in England. He said the data came from recent and well-designed studies that involved people who were initially healthy, as well as people who already had heart disease or were at risk for it.
The findings will be detailedin today's (March 18) issue of the journal Annals of Internal Medicine.
Chowdhury and colleagues carried out the study to shed light on the role of fat in coronary heart disease. Uncertainties about this role have raised questions about the optimum amounts and types of fat people should eat.
Some guidelines have suggested that eating more polyunsaturated fats, which are found in high levels in foods such as salmon, walnuts and sunflower seeds, may lower the risk of heart disease.
The researchers examined data from population studies of diets, and also looked at markers of fatty acid levels in the blood, which are considered a more accurate measure of eating patterns than self-reported diet information.
The analysis showed that when it came to eating specific types of fat — such as linoleic acid and arachidonic acid, which are both polyunsaturated fatty acids — the effects of the fat on cardiovascular risk varied widely, even when the researchers looked at members of the same family of fats, Chowdhury told Live Science.
Another analysis reviewed for the new study found no evidence that supplementing with omega-3 or omega-6 fatty acids could reduce heart disease risk, Chowdhury said.
But the researchers said that more research is needed, especially to determine if omega-3 supplements may help prevent heart disease in healthy people. (In fact, a study out this week in JAMA Internal Medicine suggested taking omega-3 supplements doesn't reduce risk of heart disease.)
What should people make of these results?
"We believe that a more 'food-focused' approach should be considered so that people consume the fatty-acid food sources that are beneficial — or not harmful to —cardiovascular health rather than pills," Chowdhury said. [11 Surprising Facts About the Circulatory System]
But these findings are not a reason to add foods such as red meat, bacon and cream, which are loaded with saturated fat, to the diet, the researchers said. Other research has suggested that when some people attempt to eat less saturated fat, they often eat more carbohydrates instead, rather than making healthier food choices.
When avoiding red meat and processed meats, people should replace those foods with nuts, fatty fish and healthy oils rather than with white rice, white bread, potatoes, sugary drinks or other refined carbohydrates, Chowdhury said.
"These data do not change the need for consuming a heart-healthy diet, they simply point out that not all fatty acids are created equally," said Linda Van Horn, a professor of preventive medicine and a research nutritionist at Northwestern University Feinberg School of Medicine in Chicago and American Heart Association spokeswoman, who was not involved in the study.
Van Horn said the paper questions the strength of the evidence underlying recommendations for eating a lot of polyunsaturated fats or limiting saturated fats. But the study stops short of making clear exactly what "high" and "low" mean, as well as determining what people's total fat intake should be, she said.
"The findings don't change anything that is in the American Heart Association (AHA) recommended diet because the study does not say that saturated fat is not a problem," Van Horn told Live Science. The AHA currently recommends that no more than 6 percent of a person's total daily calories come from saturated fat.
Saturated fats and trans fats should still be limited in the diet, she said. And polyunsaturated fats, such as safflower oil, and monounsaturated fats, like olive oil, are still useful for cooking.
"A diet high in fruits, vegetables, whole grains, unsalted nuts and fish remains the best course of action to achieve a heart-healthy diet," Van Horn said.