Every once in a while, an important nutrition research study is published and immediately becomes the Mick Jagger of the scientific and media world. Such a paparazzi-worthy study was published last year in the Annals of Internal Medicine and challenged decades-old guidance regarding dietary fat intake.
Despite a long history of recommending low total fat intake (particularly saturated fat), in recent years, some studies have questioned this recommendation. These studies’ findings suggested that perhaps saturated fat might not be the arch enemy of cardiac health, after all.
However, until the publication of this meta-analysis, the subject had not come to the attention of the public in such a forceful way. This particular meta-analysis looked at the associations between fatty acids and coronary heart disease (CHD), reviewing numerous prior studies, each with thousands of participants, warranting a closer look to determine whether its conclusions should challenge years of research pointing to the importance of minimizing saturated fat intake.
The study had some important findings:
- No Observed Associations
- In prospective studies, dietary intake of omega-6 polyunsaturated fatty acids (PUFAs) was not associated with CHD.
- No associations (in dietary intake studies or circulating fatty acid composition) were observed between total and individual intake of monounsaturated fatty acids (MUFAs) and risk of heart disease, consistent with available data.
- No associations were found between total saturated fatty acids and coronary risk in studies using dietary intake or circulating biomarkers.
- Observed Associations
- Omega-3 PUFAs were associated with lower risk of cardiovascular disease.
- As is widely accepted, total trans fatty acid intake was positively associated with coronary disease risk.
Like all research, this study has its strengths and weaknesses. The authors conducted a systematic review and meta-analysis (considered to be of the highest level of scientific evidence) of prospective, observational studies and randomized, controlled trials (RCTs), with data collected from more than 600,000 participants in 18 countries. However, although the sheer number of subjects is impressive, the large body of evidence draws different conclusions regarding saturated fats and heart health, which the authors do not adequately acknowledge. Additionally, self-reported intake data collected in observational studies is not as accurate as the controlled environment offered by a RCT.
The “Rock Stars” of Fatty Acids
Many in the research community have pointed out that these findings may be misleading due to the omission of important feeding studies and studies examining PUFAs. At the crux of the issue, however, is the question of what should replace saturated fat in the diet. For example, evidence suggests that if saturated fat is replaced in the diet with refined starch or sugars, then the relative risk for heart disease is unchanged. But, if saturated fat makes up more than the recommended 10 percent of calories, then replacing saturated fats with PUFAs (e.g. seafood, soybean and canola oils, walnuts, and flaxseed) will have a positive effect on heart disease risk. Replacing saturated fat with MUFAs (e.g. olive and canola oils, lean meats, avocados, almonds, and peanuts) may also have a positive effect on heart health, but more RCTs need to be conducted in order to confirm the possible benefits.
(I Can’t Get No) Satisfaction?
Ultimately, the study concludes that current evidence “does not yield clearly supportive evidence for current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of saturated fats.” The authors do state, however, that the findings from these studies should be interpreted with caution, not only because of differences in study design and populations between studies, but because of the relatively small number of studies looking at the benefits of alpha-linolenic and omega-6 PUFAs for heart health which, if available, could impact the conclusion.
As with all science that is evolutionary rather than revolutionary, further research is needed to add to the understanding of dietary fats and risk of CHD. Similarly, future nutrition guidance will take the findings of this meta-analysis into consideration as another piece of the puzzle.
You Can Get the Fat That You Want (and Need)
For a review of dietary fat consumption recommendations, the 2010 Dietary Guidelines for Americans (Chapter 3) is an excellent resource. Keep in mind that the scientific evidence and resulting guidance is currently being reviewed and will be updated based on the latest available science in the 2015 Dietary Guidelines.
For help understanding the basics of fats, fatty acids, and the foods that contain them, be sure to check out IFIC Foundation’s latest resource on the topic, “Dietary Fats: Balancing Health & Flavor.”