UPDATED* - A high-profile study published in the Annals of Internal Medicine last week has re-opened the debate about whether saturated fat has been unfairly cast in the role of nutritional bogeyman. But how should policymakers respond?
*EDITOR'S NOTE MARCH 25 - Since this article was published, the meta-analysis has been revised to amend the conclusions about long-chain omega-3 fatty acids (click HERE ), but the sections on saturated fatty acids and omega-6 fatty acids have not changed. Click HERE for details.
The meta-analysis analyzed data from 600,000+ subjects in 49 observational studies and 27 randomized controlled trials investigating coronary disease risk and fatty acid intake, and concluded that “current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats”.
Its conclusions echo those of a meta-analysis published in the American Journal of Clinical Nutrition (AJCN) in 2010, which found “no significant evidence … that dietary saturated fat is associated with an increased risk of coronary heart disease”.
So how should the committee currently working on the 2015 Dietary Guidelines for Americans respond?
The powerful HDL (‘good’) cholesterol raising effect of saturated fat has been completely neglected by nutrition policy makers
One firm that thinks policymakers should sit up and take notice is palm oil giant Loders Croklaan, which says the issue is top of mind for formulators in the wake of the FDA’s current proposal to revoke the GRAS status of PHOs (partially hydrogenated oils), with many commentators warning against using palm oil instead owing to its high saturated fat content.
The firm's VP of R&D Gerald McNeill PhD told FoodNavigator-USA that pressure to cut saturated fat from butter and tropical oils such as palm and coconut oil ironically led to the widespread use of PHOs (which create harmful artificial trans fats), and the replacement of fats in general with carbs.
“The net result of focusing on saturated fat reduction was a significant raising of heart disease in the population,” claimed Dr McNeill.
Once it became clear that trans fats were bad news, the industry started ditching PHOs and palm oil usage went up again; but in recent years, it has come under renewed attack from groups claiming its high saturated fat content (40-50%) is a health risk because it raises LDL (‘bad’) cholesterol, he said.
Policymakers need to re-evaluate the role of saturated fat, and focus on more pressing nutrition issues
But by narrowly focusing on LDL, palm oil’s critics have missed a trick, claimed Dr McNeill.
“For decades the powerful HDL (‘good’) cholesterol raising effect of saturated fat has been completely neglected by nutrition policy makers, who considered only one marker (LDL), making saturated fat look much worse that it really is.”
He added: “Saturated fats are considered ‘bad’ because they increase serum LDL. However, high levels of HDL are associated with reduced risk of heart disease. Saturated fat also increases serum HDL, about the same relative amount as LDL, therefore approximately cancelling out the bad effect of LDL. In fact saturated fat increases HDL cholesterol more than any other major food ingredient.
“Using the much more accurate indicator of risk of heart disease - total:HDL ratio - saturated fat is expected to have no effect on heart disease, aligning exactly with the results of this meta-analysis.”
With “overwhelming results of excellent observational studies and the positive effect of HDL on saturated fat”, he argued, “policy makers need to re-evaluate the role of saturated fat, and refocus on more pressing nutrition issues”.
National Dairy Council: Milk fat may have unique properties that differentiate it from other fats
Greg Miller, PhD, MACN, executive vice president of research, regulatory and scientific affairs at the National Dairy Council, agrees that "the theme of this latest paper is that current recommendations to reduce saturated fat are not consistent with the available data, and that there is little or no effect of saturated fat on heart disease risk."
But he also stresses that not all saturated fatty acids are equal and that "milk fat may have unique properties that differentiate it from other fats".
He added: "Blood levels of a specific fatty acid [margaric acid] that is considered an indicator of milkfat intake were associated with reduced risk for coronary outcomes."
Penny Kris-Etherton: These data conflict with a large evidence base
So should the 2015 DG committee start re-writing the rules on fats?
Penny Kris-Etherton, PhD, RD, professor of nutrition at Pennsylvania State University, is not so sure, observing that the authors' conclusions are not consistent with the Lifestyle Guideline for CVD risk reduction only just issued by the American Heart Association (AHA) and the American College of Cardiology (ACC), which is based on "five years of work by elite scientists that were appointed by the federal government and highly respected professional organizations".
Not surprisingly, therefore, the meta-analysis was a hot topic at the AHA Nutrition Committee meeting last week - and needs careful review before we start throwing out the baby with the bathwater, she told FoodNavigator-USA.
For a start, she said, "These data conflict with a large evidence base that shows benefits of unsaturated fatty acids and adverse health consequences of saturated and trans fatty acids.
"This meta-analysis shows benefits of individual long chain n-3 fatty acids, but not of the composite long chain omega-3 fatty acids (EPA & DHA) which is perplexing [EDITOR'S NOTE - THIS IS THE PART OF THE PAPER THAT HAS SINCE BEEN AMENDED ]. The lack of adverse consequences of trans fatty acids in the Annals paper is very surprising."
The trans fat results and the omega-3 fatty acid results call into question the other results the authors report
She added: "On the basis of these results, I believe a very thorough assessment is needed of the methods the authors of the Annals paper used to collect the data and analyze it. The trans fat results and the omega-3 fatty acid results call into question the other results the authors report. Because of this, the scientific community must carefully review all aspects of the current paper."
Click HERE to read more about concerns expressed by some scientists about the paper.
Increases in BMI, ageing and gender have bigger effects on heart disease risk
Dr Tom Sanders, Professor of Nutrition & Dietetics at Kings College London, also noted that “the biomarkers which were used in the study are hopeless for estimating intakes of saturated and mono-unsaturated fats [something the authors acknowledge].”
But what about its overall conclusions?
He told FoodNavigator-USA: “I gather there is now a series of ‘best-sellers’ [in the pipeline] that say we got it all wrong about dietary fat. That is a bit simplistic.
“There is no doubt that LDL cholesterol causes coronary heart disease but you need another component and that is inflammation. Smoking plus high blood cholesterol were a lethal combination in the Western world.
“The lipid hypothesis I think is proven; it is just that modifying dietary fat composition does not have a huge effect. Increases in BMI, ageing and gender have bigger effects… Differences in SFA intake only explain about 5% of the variance in blood cholesterol levels between individuals in cross-sectional studies.”
Dietary patterns are probably more important than single nutrients
But he cautioned: “I don't think this paper is a carte blanche to eat lots of fatty meat and cream. The bottom line is that dietary patterns are probably more important than single nutrients.”
EDITOR'S NOTE MARCH 25 - Since this article was published, the meta-analysis has been revised to amend some of the data on long-chain omega-3 fatty acids, but the sections on saturated fatty acids and omega-6 fatty acids have not changed.
The revised version notes that "dietary long-chain omega-3 polyunsaturated fatty acids WERE associated with lower risk of coronary disease".
Click HERE for details.
Source: Annals of Internal Medicine
2014, Volume 160
‘Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk – A Systematic Review and Meta-analysis’
Authors: R. Chowdhury, S. Warnakula, S. Kunutsor, et al.