CV Risk and Saturated Fats: The Debate Roils On

March 17, 2014

CAMBRIDGE, UK — A meta-analysis has revived the debate over best dietary recommendations for cardiovascular health; specifically, whether there's an evidence base supporting the traditional message to consume foods rich in long-chain omega-3 and omega-6 polyunsaturated fatty acids (PUFA) and avoid those laden with saturated fats[1]. But questions about the report emerged even before its publication today.

"We found essentially null associations between total saturated fatty acids [SFA] and coronary risk" in studies looking at dietary fat intake and those focusing on circulating fatty-acid levels, according to the authors, led by Dr Rajiv Chowdhury (University of Cambridge, UK). Nor were there significant associations between CV risk and dietary intake of long-chain omega-3 and omega-6 PUFAs. Other findings suggested that dietary supplements containing those fatty acids don't significantly reduce coronary risk.

The group's meta-analysis of over 70 reports, including prospective cohort studies and randomized trials, is published in the March 18, 2014 issue of the Annals of Internal Medicine.

"Our findings do not support cardiovascular guidelines that promote high consumption of long-chain omega-3 and omega-6 and polyunsaturated fatty acids and suggest reduced consumption of total saturated fatty acids," they write.

The analysis shows "no strong evidence" to justify those cardiovascular guidelines, "especially for saturated fat," senior author Dr Emanuele Di Angelantonio (University of Cambridge) told heartwire . So there's a need for further trials to explore the issue, he said, to determine just what the recommendations should be.

But the meta-analysis has already been questioned. In an email exchange with heartwire , Dr Eric B Rimm (Harvard School of Public Health, Boston, MA) said, "My colleagues were quite surprised at the findings. We uncovered a serious mistake in their review of PUFA that likely will change the results substantially." And the parts of the meta-analysis focusing on PUFA didn't summarize the relevant studies correctly, according to Rimm, who added that "the results are in serious question."

Moreover, the group's conclusion about saturated fat "has little context, because it likely represents the result of when you exchange saturated fat in your diet for refined grain. Thus, saturated fat is no better or worse than eating white bread. We have known that for decades, so [it] is not new."

Rimm said he and his colleagues have contacted the report's authors about their issues with the analysis.

Also contacted by heartwire , Dr Alice H Lichtenstein (Tufts University, Boston, MA) replied by email, "The majority of the evidence suggests that replacing saturated fat with polyunsaturated fat reduces heart disease risk, whereas replacing saturated fat with carbohydrate does not. This new study only assessed one factor, an indicator of dietary fat, and not the whole picture, making the conclusions questionable."

Regarding assertions of errors in the report, Di Angelantonio said, "We recently spotted some minor mistakes in some of the data that will not in any way affect the main results of the study." He confirmed that another group contacted him and his coauthors about "some other minor mistake," adding, "We are making an erratum that will be sent to [Annals of Internal Medicine] in the next 24 hours, so there will be an updated version. But it's unlikely that the main conclusions will change."

As for the analysis itself, it covered 45 prospective observational studies and 27 randomized controlled trials looking at dietary PUFA intake, levels of circulating PUFA, and intake of fatty-acid dietary supplements in populations throughout the most of the world.

Relative Risk (95% CI) for Coronary Events, Top vs Bottom Third of Total Dietary Fatty-Acid Intake Levels in Prospective Cohort Studies*

Fatty-Acid Type RR (95% CI)
Saturated 1.02 (0.97–1.07)
Monosaturated 0.99 (0.89–1.09)
Long-chain omega-3 0.93 (0.84–1.02)
Omega-6 1.01 (0.96–1.07)
Trans 1.16 (1.06–1.27)

*32 studies, 530 525 participants, mean follow-up 5–23 years. All adjusted for age, sex, smoking, diabetes, and blood pressure, and other influences on CV risk

"Among studies with available data," the group writes, "there were moderate positive correlations between dietary intake and circulating composition of total omega-3 and omega-6 polyunsaturated fatty acids and weak positive correlations for total saturated and monounsaturated fatty acids."

Relative Risk (95% CI) for Coronary Events, Top vs Bottom Third of Circulating Fatty-Acid Levels in Prospective Cohort Studies*

Fatty-Acid Type RR (95% CI)
Saturated 1.06 (0.86–1.30)
Monosaturated 1.06 (0.97–1.17)
Long-chain omega-3 0.84 (0.63–1.11)
Omega-6 0.94 (0.84–1.06)
Trans 1.05 (0.76–1.44)

*19 studies, 32 307 participants, mean follow-up 1.3–30.7 years

Also, there was evidence that "circulating levels of eicosapentaenoic and docosahexaenoic acids . . . and arachidonic acid are each associated with lower coronary risk."

Consistent with the literature and guidelines, total dietary trans-fatty-acid intake was positively associated with coronary disease risk.

Relative Risk (95% CI) for Coronary Events in Randomized Trials, Fatty-Acid Dietary Supplements vs Control Group*

Parameter RR (95% CI)
Alpha linolenic 0.97 (0.69–1.36)
Long-chain omega-3 0.94 (0.86–1.03)
Omega-6 0.89 (0.71–1.12)

*27 trials, 103 052 participants, mean follow-up 0.1–8 years

Di Angelantonio pointed out that his group's analysis is not the first to question the evidence base for an adverse effect of dietary saturated fat on cardiovascular health.

Primary funding was provided by the British Heart Foundation, Medical Research Council, Cambridge National Institute for Health Research Biomedical Research Centre, and Gates Cambridge. Chowdhury declared no conflicts of interest; disclosures for the coauthors are listed in the report.

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