March 17th, 2014
05:00 PM ET
Many health organizations, including the American Heart Association, recommend eating polyunsaturated fatty acids - particularly those called omega-3s and omega-6s - for heart health. But new research once again casts doubt on whether these fatty acids have any effect on reducing your risk of heart disease.
A meta-analysis published Monday in the journal Annals of Internal Medicine did not find significant evidence to support eating a diet high in polyunsaturated fatty acids and low in saturated fats. It didn't seem to matter whether the fats came from dietary sources or supplements.
"Current evidence does not clearly support guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats," the study authors concluded.
And a second study, published in the journal JAMA Internal Medicine, found that supplementing a diet with long-chain omega-3 polyunsaturated fatty acids did not reduce study participants' heart disease risk.
Fatty fish such as salmon, trout and herring all have high levels of polyunsaturated fats; so do nuts, seeds and several vegetable oils, according to the American Heart Association. Monounsaturated fats can be found in olive oil, canola oil, avocados and peanut butter, for example. The AHA recommends that most fats you eat be polyunsaturated or monounsaturated.
A meta-analysis looks at past studies to see if patterns in the data hold up across many experiments. In that sense, the research method is stronger than just one study. But there could be inaccuracies and biases in the individual studies analyzed, as well as methodological differences among them that make conclusions about the combined findings more complicated.
The first study
For this new meta-analysis published in Annals of Internal Medicine, researchers reviewed a large spectrum of studies on the subject: 32 observational studies looking at fatty acids from dietary intake, 17 observational studies of fatty acid biomarkers, and 27 randomized, controlled trials examining fatty acid supplementation.
Focusing on the randomized trials of supplementation, the meta-analysis found that long-chain omega-3 and omega-6 polyunsaturated fatty acids did not reduce the likelihood of coronary events. But further study of this subject is warranted, researchers wrote, as "the available evidence is generally limited."
The meta-analysis found no consistent association between a person's total saturated fatty acid intake and his or her coronary risk. Researchers also did not find an association between monounsaturated fatty acid consumption and coronary risk.
The second study
A second study published Monday also failed to find fatty acids lead to a risk reduction in cardiovascular events.
Research in the journal JAMA Internal Medicine found that supplementing a diet with long-chain omega-3 polyunsaturated fatty acids did not reduce a person's risk of cardiovascular disease. Researchers analyzed data from 4,203 elderly people with age-related macular degeneration.
So what's going on? There are a few shortcomings in this study, Dr. Evangelos Rizos and Dr. Evangelia Ntzani wrote in an accompanying commentary. For instance, 20% of the study participants had known cardiovascular disease, and participants were aware of which treatment they were receiving. The authors also did not publish information about participants' triglyceride levels, which are thought to be reduced by omega-3 supplementation.
Given the lack of evidence in previous studies for omega-3 supplementation, Rizos and Ntzani said that more similar randomized trials would be "unjustified." They instead call for a meta-analysis and for trials that "focus on the remaining gaps of knowledge" such as studying the effect of high doses of omega-3s on patients with high levels of triglycerides.
"Patients raising the question of taking omega-3 supplements should be informed of the uncertainty surrounding their choice, and regular dietary consumption of (whole) fish should be preferentially encouraged as a source (of these fatty acids)" instead of supplements, Rizos and Ntzani wrote.
International guidelines do not agree on how much, and which types, of fatty acids are best to eat. There is no reason to change the current guidelines put forth by the American Heart Association, said Linda Van Horn, spokeswoman for the AHA. She said this study's results are not surprising.
The general advice - avoid trans fats, reduce saturated fat, increase intake of fruits, vegetables and whole grains - still stands, Van Horn said.
Duffy MacKay, senior vice president for scientific and regulatory affairs at the Council for Responsible Nutrition, said in a statement that the researchers of the Annals of Internal Medicine study raise an "interesting viewpoint" but a "potentially irresponsible one."
"Unfortunately, their conclusions, if taken to heart, leave consumers to rely on genetics and fate to avoid coronary heart disease - an unacceptable situation given the fact that the scientific literature contains so many studies that point to benefit for omega-3 fatty acids," MacKay said.
The AHA is holding a national meeting this week; experts there will have the opportunity to "consider what this paper means," Van Horn said.
About this blog
Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.