Conventional medical wisdom about heart health rests on evidence that in general, diets high in saturated fats and low in polyunsaturated ones raise heart risks slightly to modestly.
But this official advice has never acknowledged the abundant and growing evidence that the story is just not that simple.
First, context matters. Studies in which people consume the same amounts and proportions of saturated fat within different diets yield very different outcomes.
The most prominent – but far from uncommon – example is the so-called “French Paradox”. (The French diet is high in saturated fat, but that nation has lower rates of heart disease than America does.)
Second, it matters which of the various forms of saturated fat people consume the most, because each has different effects on blood fat profiles and heart risk, with some having no negative impacts.
Third, despite what we’ve been told for decades, it’s far from clear that replacing saturated fat with the polyunsaturated omega-6 fats that predominate in most common vegetable oils is beneficial … especially in light of the negative, inflammatory effects that accompany “over-substitution” of saturated fats with omega-6 fats (see “Polyunsaturated fats aren’t interchangeable”, below).
So it’s encouraging to see leading researchers challenge the scientifically sloppy scapegoating of saturated fats … and to see that critique make waves at a major food science/technology summit.
Is saturated fat the real heart villain?
The debate about just how bad saturated fats really are for our health – and whether what we are replacing them with is potentially worse – received high profile exposure at last month’s Institute of Food Technologists (IFT) Expo in New Orleans.
The debate was fueled by a lecture on public health advice about fat consumption, delivered by Dr. Rozenn Lemaitre … a prominent heart-health researcher from the cardiovascular research unit at the University of Washington.
She noted that saturated fat reduction is conventional, poorly examined wisdom … and that we should be more concerned about the food factors that replace it … especially refined carbohydrates.
And as she said, the evidence linking saturated fat and risk of cardiovascular disease is “not conclusive”, and must be considered in the context of its replacement by refined carbohydrates.
Others raised the overlooked evidence that the decades-long policy of replacing saturated fats – like butter and lard – with even greater quantities of mostly polyunsaturated vegetable oils high in omega-6 fats has had dire consequences.
Their comments dovetailed with the debate sparked by a high profile meta-analysis (review of prior studies) published last year by researchers at Harvard and Children’s Hospital Oakland, which found “no significant evidence … that dietary saturated fat is associated with an increased risk of coronary heart disease [CHD] or cardiovascular disease [CVD].” (Siri-Tarino PW et al. Am J Clin Nutr. 2010 Mar;91(3):502-9)
In a second study, the same scientists echoed Dr. Khosla’s point: “More data are needed to elucidate whether CVD risks are likely to be influenced by the specific nutrients used to replace saturated fat.” (Siri-Tarino PW et al. Am J Clin Nutr. 2010 Mar;91(3):535-46)
Scientists gathered at a symposium in Copenhagen last May also pointed out that individual saturated fatty acids have different cardiovascular effects, making a person’s general saturated fat intake a poor gauge of risk.
They also noted that major food sources of saturated fat such as milk contain other constituents that could reduce the risk of heart disease.
As for replacing saturated fats with monounsaturated fats (e.g., olive oil, macadamia nut oil, hi-oleic sunflower oil, canola oil, avocados), they concluded that “insufficient evidence exists to judge the effect on coronary heart disease risk of replacing saturated fatty acids with [monounsaturated fatty acids]” (Astrup A et al. 2011).
Polyunsaturated fats aren’t interchangeable: Your omega-3/6 balance matters
Commenting on the debate at the FTI Expo, Dr. Pramod Khosla of Wayne State University in Detroit raised a key point:
“Saturated fat per se is not really doing anything [harmful] when it comes to cardiovascular disease risk. What’s more crucial is to look at what people are replacing it with.”
The U.S. 2010 Dietary Guidelines for Americans advise people to consume less than 10 percent of calories from saturated fatty acids by replacing them with monounsaturated and polyunsaturated fats.
But evidence continues to grow showing that this official advice needs urgent adjustment.
Captain Joseph Hibbeln, M.D. – a leading fatty acid researcher at the National Institutes of Health (NIH) – commented that it would have been “more helpful” if those guidelines had been specific about which polyunsaturated fats to favor … lest they do more harm than good.
As he noted, “A clear distinction should be made between omega-6 and omega-3 polyunsaturated fats in future advice.”
Five years ago, Dr. Hibbeln and renowned fatty acid researcher William E. Lands, Ph.D., co-authored a landmark evidence review that linked the overload of omega-6 fats in Western diets to their high rates of heart disease, dementia, and more … see “Report Finds Americans Need More Omega-3s ... and Far Fewer Omega-6 Fats.”
That study and others show that consuming too many of the omega-6 polyunsaturated fats in soy foods and common vegetable oils (e.g., soy, corn, safflower, and cottonseed) is inherently unhealthful.
At the same time, few Americans get enough of the more heart-beneficial omega-3s … whether the plant form omega-3 (ALA) in beans, dark leafy greens, walnuts, and flaxseed, or, better yet, EPA and DHA, which the body can absorb from fish fat, or can make – but very inefficiently – from ALA.
Dr. Hibbeln said that the ratio of omega-6 to omega-3 fatty acids in the modern diet is currently far out of kilter, with Americans now getting almost 10 percent of their calories from omega-6 fats due to excessive consumption of vegetable oils and the many prepared or packaged foods high in them.
He went on to stress that omega-6s exert pro-inflammatory effects, and that excess consumption of them makes it more difficult for the body to convert the short-chain omega-3s in plant foods into the long-chain omega-3s (EPA and DHA) essential to brain, cardiovascular, and overall health.
As we reported, he and his colleagues published a stunning study proving that claims about the benefits of omega-6 fatty acids made by the American Heart Association were based on clinical studies in which participants had been consuming both omega-3s and omega-6s, yet the conclusions ignored the omega-3s. (See “Heart Group's Omega-6 Advice Takes a Huge Hit”.)
“If you pool results of trials just looking at omega-6 polyunsaturated fats you see no heart benefit … they actually signal harm.”
For more on the effects of America’s “omega imbalance”, see the Omega-3 / Omega-6 Balance section of our news archive.
Astrup A, Dyerberg J, Elwood P, Hermansen K, Hu FB, Jakobsen MU, Kok FJ, Krauss RM, Lecerf JM, LeGrand P, Nestel P, Risérus U, Sanders T, Sinclair A, Stender S, Tholstrup T, Willett WC. The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: where does the evidence stand in 2010? Am J Clin Nutr. 2011 Apr;93(4):684-8. Epub 2011 Jan 26. Review.
Hu FB, Stampfer MJ, Manson JE, Ascherio A, Colditz GA, Speizer FE, Hennekens CH, Willett WC. Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women. Am J Clin Nutr. 1999 Dec;70(6):1001-8.
Lemaitre R. Cell membrane fatty acids and coronary heart disease. Institute of Food Technologists (IFT) Expo, New Orleans, June 2011. Accessed at http://www.ift.org/meetings-and-events/past-meeting-resources/technical-abstracts-search/Abstract Search Details.aspx?id=50857&techtitle=Cell membrane fatty acids and coronary heart disease
Micha R, Mozaffarian D. Saturated fat and cardiometabolic risk factors, coronary heart disease, stroke, and diabetes: a fresh look at the evidence. Lipids. 2010 Oct;45(10):893-905. Epub 2010 Mar 31. Review.
Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. 2010 Mar;91(3):535-46. Epub 2010 Jan 13
Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Saturated fat, carbohydrate, and cardiovascular disease. Am J Clin Nutr. 2010 Mar;91(3):502-9. Epub 2010 Jan 20. Review.