Two new studies raise yet more questions about current dietary guidelines for a healthy heart — specifically the recommendations to eat less saturated fat and more polyunsaturated fats, including omega-3 fatty acids.
The studies found that both types of fat appear to have no effect — neither bad nor good — on the risk of heart disease.
Saturated fat is the kind found mainly in fatty meats and whole-milk dairy products. Polyunsaturated fats generally come from plant-based foods, primarily nuts, flaxseeds, avocados and certain vegetable oils, such as olive and canola. Omega-3 fatty acids are a type of poloyunsaturated fat. One of its key sources is fish, especially salmon and sardines.
Study #1
The first study, published Monday in the Annals of Internal Medicine, was a meta-analysis. It examined data from 72 randomized and observational studies involving more than 500,000 people. These studies not only looked at what people said they ate, but some also measured the amount of fatty acids in their blood and tissue, a more objective assessment.
Twenty-seven of the studies were randomized controlled trials — the “gold standard” of clinical research studies — that gave participants either a polyunsaturated supplement (such as fish oil) or a placebo, and then followed them to see if the supplement had any effect on their risk of heart disease.
The meta-analysis found that saturated fats had no noticeable negative effect on people’s heart disease risk. Nor did polyunsaturated fats have a statistically significant positive effect on that risk.
Only trans fats — the artificially created partially hydrogenated vegetable oil found in many fast foods and processed bakery goods — was confirmed as being associated with an increased risk of heart disease.
“The pattern of findings from this analysis did not yield clearly supportive evidence for current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of saturated fats,” concluded the study’s authors.
Study #2
The second study, published Monday in the journal JAMA Internal Medicine, was a randomized controlled trial involving more than 4,000 people with age-related macular degeneration (AMD), a progressive and debilitating eye disease that is the leading cause of severe vision loss and legal blindness among older Americans.
The study, called Age-Related Eye Disease Study 2 (AREDS2), has been trying to determine if omega-3 supplements could help slow down the progression of AMD. The researchers running the study decided to also look at whether the supplements reduced the risk of heart disease.
In 2013, the AREDS2 researchers reported that taking omega-3 fatty acid supplements has no effect on the progression of AMD. In the new study, they report that it also does not reduce the risk of heart disease.
People in the study who were randomized to take omega-3 supplements (350 milligrams of DHA and 650 milligrams of EPA) were just as likely after five years to have a stroke, a heart attack or die from heart disease as those who took a placebo.
“Our results are consistent with a growing body of evidence from clinical trials that have found little [cardiovascular] benefit from moderate levels of dietary supplementation,” the authors conclude.
Needed: ‘A careful reappraisal’
In a press statement released with the Annals of Internal Medicine study, Dr. Rajiv Chowdhury, the University of Cambridge cardiovascular epidemiologist who led the study, said it was time for “a careful reappraisal of our current nutritional guidelines.”
The need for that reappraisal is urgent for, as Chowdhury also noted in the press statement, cardiovascular disease is the single-leading cause of death and disability worldwide.
Here in the United States, more than 600,000 people die of cardiovascular disease each year, making it the leading cause of death for both men and women, according to the Centers for Disease Control and Prevention.
“With so many affected by this illness,” said Chowdhury, “it is critical to have appropriate prevention guidelines which are informed by the best available scientific evidence.”
Marker studies
Again, these appear to be marker studies: ones that look at measures of health which are assumed to have an impact on mortality, rather than at mortality itself. This is only an assumption.
We need a direct measure of the effect on mortality of specific diets.
And there is the usual problem of meta analyses (literally: ‘beyond analysis’). The assumption is that combining a large number of small (and imperfect) studies will produce the same outcome as a single large well controlled study. This assumption does not always hold up.
We need more of our resources directed to the kind of research necessary to answer these good questions.
Question the assumptions
It seems the studies focus on supplements, not real food. It may be premature to draw conclusions about best eating habits based on studies of supplements.