第一篇大意便是如果把所有不同的脂肪酸进一步分类，那么不同的脂肪酸影响效果不一样，饮食中和血液中omega3，omega6与心血管事件呈负相关，而饱和脂肪和反式脂肪与心血管事件正相关。

CV Risk and Saturated Fats: The Debate Roils On

Steve Stiles

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*

*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*

*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*

Not All PUFAs Created Equal, Say Researchers

Michael O'Riordan

November 14, 2013

TORONTO, ON – Not all polyunsaturated fatty acids (PUFAs) are created equal, according to a new report, so simply replacing dietary saturated fats with polyunsaturated fatty acids might not be enough to lower the risk of heart disease^[1].

In an analysis published November 11, 2013 in CMAJ, two researchers argue that to obtain the "heart benefits" of polyunsaturated fatty acids, the emphasis should be on α-linolenic acid, an omega-3 fatty acid, and not on linoleic acid, which is an omega-6 fatty acid.

Given their concerns, Dr Richard Bazinet (University of Toronto, ON) and Dr Michael Chu (Western University, London, ON) argue that a broad cholesterol-lowering health claim for omega-6 fatty acids be reexamined. "We suggest that the health claim be modified such that foods rich in omega-6 linoleic acid but poor in omega-3 α-linolenic acid be excluded," they write.

In 2009, Health Canada's Food Directorate allowed a claim for polyunsaturated fatty acids by stating that when they replace saturated fats in the diet, there is a statistically significant reduction in total- and LDL-cholesterol levels, and the result is a reduction in the risk of coronary heart disease.

Not All PUFAs Have Same Effect

In their report, the Canadians argue that the full effects of substituting saturated fats with vegetable oils rich in polyunsaturated fats are not entirely clear. In a review of the data, they state there is "doubt as to whether the protective effects can be attributed to linoleic acid."

In one meta-analysis examining the sources of fatty-acid composition, the risk of cardiovascular death and MI was 22% lower when oils with a mix of α-linolenic and linoleic acid were used. "However, the rates of nonfatal myocardial infarction and death from coronary artery disease were not significantly lower when oils made up mostly of linoleic acid but relatively low in α-linolenic acid were substituted," write Bazinet and Chu.

The research also showed that soybean oil, which contains a mix of α-linolenic and linoleic acids, had a protective effect against coronary heart disease, but corn and safflower oils, which are rich in linoleic acid, did not. Data from the Sydney Diet Heart Study (SDHS) also revealed that safflower oil lowered LDL-cholesterol levels 8% to 13% but was associated with an increased risk of cardiovascular mortality.

For this reason, oils rich in linoleic acid should not be grouped together with oils that contain a mix of α-linolenic and linoleic acids, state Bazinet and Chu. They agree that it is not entirely possible to draw strong conclusions from the published data and that the reasons why linoleic acid was associated with increased cardiovascular mortality in SDHS are unclear. Still, they urge Health Canada to separate the two polyunsaturated fatty acids.

Bazinet reports support from Bunge, Unilever, and Kraft Foods. Chu reports support from Medtronic, Edward Lifesciences, and NeoChord.