The findings, published in the Annals of Internal Medicine, have sparked renewed debate about fats and heart health.
The new study should trigger a review of current diet guidelines for heart health, according to the researchers who did the analysis. Other experts, including one from the American Heart Association, disagree.
There is some common ground. All agree that dietary fat is just one factor that drives heart disease risk. Paying attention to the other factors is also important.
WebMD asked a study co-author, a cardiologist, a nutrition expert, and the American Heart Association to elaborate.
What did the analysis look at and find?
Researchers looked at 72 published studies on fats and heart disease. The studies involved more than 600,000 people from 18 countries. Some people already had heart disease, while others did not. The researchers reanalyzed the results, an approach called a meta-analysis.
They looked at whether different fats helped or hurt your heart. The different fats included:
- Saturated fats (found in meats, whole-fat dairy products, and baked goods)
- Polyunsaturated fats, such as omega-3 and omega-6 (found in fish, nuts, seeds, and vegetable oils)
- Monounsaturated fats (found in olive and canola oils)
- Trans fats (found in fried foods and baked goods, and being phased out of the food supply)
The surprise? Saturated fats, long thought to raise heart disease risks, had no effect. Neither did monounsaturated fats, which are thought to help the heart, says study researcher Dariush Mozaffarian, MD, at the Harvard School of Public Health.
Which fats did have an effect? Trans fats, known to raise bad cholesterol and lower good cholesterol, were linked with a higher risk of heart disease, as expected. Omega-3s from food helped. Omega-6s appeared to help.
What do the researchers say about the findings?
Nutritional guidelines on fats and heart health by such organizations as the American Heart Association may deserve another look, the study authors say.
The focus should move beyond just the fat content of food, Mozaffarian says. "We can't judge the healthfulness of a food [only] by how many grams of saturated fat it has. We really should be moving toward a food-based analysis.
"It's not just the fat grams, and the type of food, but the way the food is processed," he says. For instance, the analysis found that a type of saturated fat linked with milk and dairy products reduced heart disease risk.
Based on the analysis, Mozaffarian and his colleagues say, the current heart health guidelines that promote eating more foods with omega-3s and omega-6s and less of those with saturated fats are not needed.
What do others say?
Other experts find fault with the study and its conclusions.
"Mainly I think the findings should be disregarded," says Walter Willett, MD, chair of nutrition at the Harvard School of Public Health, who was not involved in the study. While the analysis suggests that ''saturated fat is not quite as bad as its reputation, it depends on what you compare it to," he says.
"If you replace saturated fat with carbohydrates or refined starch or sugar, you are not changing your heart disease risk," he says. ''If you replace saturated fat with polyunsaturated fat, you do get a reduction in heart disease risk."
One analysis is not enough to change dietary advice, says James Blankenship, MD, director of cardiology at Geisinger Medical Center.
In the analysis, the researchers themselves cite a number of caveats and limitations, such as study participants self-reporting their fat intake.
In response to the study, the American Heart Association says its guidelines remain the same. For heart health, it recommends a diet rich in fruits and vegetables, whole grains, fish, nuts, and unsaturated fats.
Less than 6% of the diet should include saturated and trans fats, the association says.
Is there some common ground about how to protect heart health?
Judging how heart-healthy a food is must take more than fat into account, Mozaffarian says. For instance, a lower-fat meat that is processed is not heart-healthy, he says.
Willett agrees. "It's important to look at single nutrients, but also at whole food groups," he says. Blankenship offers these steps proven to benefit the heart:
- Get regular exercise -- at least a half-hour a day.
- Maintain a healthy body weight.
- See your doctor and find out your heart disease risk. Know your blood pressure and cholesterol levels.
"Don't spend so much time looking at food labels," Blankenship says. Instead, he says, go to the grocery store's produce department and load up.
If cholesterol and saturated fat don't play as large a role as we thought in heart disease, what's behind the heart disease problem?
Multiple factors, Blankenship says. They include obesity, genetics, sedentary lifestyles, diabetes, and high blood pressure. A poor diet drives risk, he says, "but it's not the only thing."
Mozaffarian reports receiving fees from Bunge, Pollock Institute, Quaker Oats, Life Sciences Research Organization, Foodminds, Nutrition Impact, Amarin, Astra Zeneca, Winston and Strawn LLP, and UpToDate, and serving on the scientific advisory board for Unilever North America.
The study was funded by the British Heart Foundation, the Medical Research Council, Cambridge National Institute for Health Research Biomedical Research Centre, and Gates Cambridge.