Saturated fat and cardiovascular disease controversy

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Whether saturated fat is a risk factor for cardiovascular disease is a question with numerous controversial views.[1] Medical, scientific, heart-health, governmental and intergovernmental, and professional authorities, such as the World Health Organization,[2] the American Dietetic Association,[3] the Dietitians of Canada,[3] the British Dietetic Association,[4] American Heart Association,[5] the British Heart Foundation,[6] the World Heart Federation,[7] the British National Health Service,[8] the United States Food and Drug Administration,[9] and the European Food Safety Authority[10] advise that saturated fat is a risk factor for cardiovascular disease, and recommend dietary limits on saturated fats as one means of reducing that risk. A 2015 systematic review presented a contrary position.[11]

History[edit]

Cholesterol and cardiovascular disease[edit]

The initial connection between arteriosclerosis and cholesterol was made by the Russian pathologist Nikolay Anichkov, prior to World War I.[12] Another significant contribution to the debate was made by the Dutch physician (internist) Cornelis de Langen, who noticed the correlation between nutritional cholesterol intake and incidence of gallstones (and soon after, arteriosclerosis and other "Western diseases") in the Javanese population in 1916.[13][14] De Langen reported on his findings at the conference of the International Society of Geographic Pathology in 1935. These observations were made on patients admitted to the municipal hospital in Jakarta. Consequently, he studied this phenomenon in defined populations outside the hospital. He showed that the traditional Javanese diet, very poor in cholesterol and other lipids, was associated with a low level of blood cholesterol as well as a low incidence of cardiovascular disease (CVD), while the prevalence of CVD in Europeans in Java, living on the Western diet, was significantly higher.[13] De Langen's colleague, Isidor Snapper, made a similar observation in North China in 1940. Since de Langen published his results only in Dutch, his work remained unknown to most of the international scientific community.[13]

Saturated fat and cardiovascular disease[edit]

The notion that saturated fat has a detrimental effect on human health gained attention for the first time in the 1950s.[15] It was promoted by Ancel Keys, a US nutritional scientist. Keys postulated a correlation between cholesterol levels and cardiovascular disease, and initiated a study of Minnesota businessmen (the first prospective study of CVD).[16] At a 1955 expert meeting of the World Health Organization in Geneva, Keys presented his diet-lipid-heart disease hypothesis.[17] At that time in the USA, the incidence of heart disease was rapidly increasing, with no apparent cause.[15] Keys reaped severe criticism at the conference. Consequently, he set out to develop the yearslong Seven Countries Study.[18]

Systematic reviews[edit]

Summary table[edit]

Systematic review Relationship between cardiovascular disease and saturated fatty acids (SFA)
Hooper, 2016[19] "The findings are suggestive of a small but potentially important reduction in cardiovascular risk on modification of dietary fat, but not reduction of total fat, in longer trials. Lifestyle advice to all those at risk of cardiovascular disease and to lower risk population groups, should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturates."
Ramsden, 2016[20] "Available evidence from randomized controlled trials shows that replacement of saturated fat with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes."
de Souza, 2015[21] "Saturated fats are not associated with all cause mortality, CVD, CHD, ischemic stroke, or type 2 diabetes, but the evidence is heterogeneous with methodological limitations."
Schwab, 2014[22] "there was convincing evidence that partial replacement of SFA [saturated fat] with PUFA [polyunsaturated fat] decreases the risk of CVD, especially in men."
Chowdhury, 2014[23] "Current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats."

Review details[edit]

A 2015 systematic review of randomized control trials by the Cochrane Library found that reducing saturated fat intake resulted in a 17% reduction in cardiovascular events, and that replacing saturated fats with cis unsaturated fats in particular is beneficial. It concluded: "Lifestyle advice to all those at risk of cardiovascular disease and to lower risk population groups should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturated fats."[24]

In 2014, a systematic review and meta-analysis of 72 published studies totaling 530,525 participants, looked at observational studies of dietary intake of fatty acids, observational studies of measured fatty acid levels in the blood, and intervention studies of polyunsaturated fat supplementation. The authors of the review 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.″[23]

However, Walter Willett, chair of the Department of Nutrition at Harvard School of Public Health, warns that the conclusions are seriously misleading, as the analysis contains major errors and omissions and should be retracted.[25] In response to the Chowdhury review, Drs. Willett, Frank Sacks, and Meir Stampfer commented that:

″The meta-analysis of dietary fatty acids and risk of coronary heart disease by Chowdhury et al. contains multiple errors and omissions, and the conclusions are seriously misleading, particularly the lack of association with N-6 polyunsaturated fat. For example, two of the six studies included in the analysis of N-6 polyunsaturated fat were wrong. The relative risks for Nurses’ Health Study (NHS) and Kuopio Ischemic Heart Disease Study (KIHD) were retrieved incorrectly and said to be above 1.0. However, in the 20-year follow-up of the NHS the relative risk for highest vs lowest quintile was 0.77 (95 percent CI: 0.62, 0.95); ptrend = 0.01 (the authors seem to have used the RR for N-3 alpha-linolenic acid from a paper on sudden cardiac death), and in the KIHD the relative risk was 0.39; 95% confidence interval [CI], 0.21-0.71) (the origin of the number used in the meta-analysis is unclear). Also, relevant data from other studies were not included.
Further, the authors did not mention a pooled analysis of the primary data from prospective studies, in which a significant inverse association between intake of polyunsaturated fat (the large majority being the N-6 linoleic acid) and risk of CHD was found. Also, in this analysis, substitution of polyunsaturated fat for saturated fat was associated with lower risk of CHD. Chowdhury et al. also failed to point out that most of the monounsaturated fat consumed in their studies was from red meat and dairy sources, and the findings do not necessarily apply to consumption in the form of nuts, olive oil, and other plant sources. Thus, the conclusions of Chowdhury et al. regarding the type of fat being unimportant are seriously misleading and should be disregarded.″

Views[edit]

Mainstream authorities[edit]

Specialist/professional textbooks[edit]

The 2009 European Society of Cardiology Textbook of Cardiovascular Medicine states that, in cohort studies, the positive relationship between fat intake and CVDs was linked to their saturated fatty acid content.[26]

2007's Cardiovascular Prevention and Rehabilitation states that large epidemiological studies have shown consistent associations between the intake of saturated fatty acids and CHD mortality.[27]

According to the 2007 Critical Pathways in Cardiovascular Medicine, substituting unsaturated fat for saturated fat may lower LDL cholesterol without simultaneously lowering HDL cholesterol. This dietary principle partly underlies the Mediterranean style of diet, which has been associated with reduced cardiovascular event rates in two randomized controlled trials.[28]

The 2003 second edition of Evidence-based Cardiology in 'PartII: Prevention of cardiovascular diseases' recommends a low intake of SFA, less than 7% of daily calories, and intake of foods rich in myristic and palmitic acids should be especially reduced. The recommendation was evaluated to be supported by the best grade of available evidence.[29]

Position statements and guidelines of major health organizations[edit]

Medical establishments[edit]

In 2003 a World Health Organization (WHO) and Food and Agricultural Organization (FAO) expert consultation report concluded that "intake of saturated fatty acids is directly related to cardiovascular risk. The traditional target is to restrict the intake of saturated fatty acids to less than 10%, of daily energy intake and less than 7% for high-risk groups. If populations are consuming less than 10%, they should not increase that level of intake. Within these limits, intake of foods rich in myristic and palmitic acids should be replaced by fats with a lower content of these particular fatty acids. In developing countries, however, where energy intake for some population groups may be inadequate, energy expenditure is high and body fat stores are low (BMI <18.5 kg/m2). The amount and quality of fat supply has to be considered keeping in mind the need to meet energy requirements. Specific sources of saturated fat, such as coconut and palm oil, provide low-cost energy and may be an important source of energy for the poor."[30]

In its 2007 guidelines, the European Society of Cardiology states that there are strong, consistent, and graded relationships between saturated fat intake, blood cholesterol levels, and the mass occurrence of cardiovascular disease. The relationships are accepted as causal.[31]

The Mayo Clinic considers saturated fats potentially harmful and monounsaturated and polyunsaturated fats potentially helpful. It references the Dietary Guidelines for Americans, 2010 and recommends reducing foods rich in saturated fat and emphasizing options with more monounsaturated and polyunsaturated fats.[32]

The British Dietetic Association guidelines found good evidence in systematic reviews of randomized controlled trials that reducing saturated fat reduces morbidity in patients with CVD.[33]

The 2007 position statement of the American Dietetic Association and the Dieticians of Canada holds that epidemiological studies have shown a positive association between the intake of saturated fatty acid and the incidence of coronary heart disease.[3]

The Harvard School of Public Health holds that saturated fats should be replaced with cis monounsaturated and polyunsaturated fats, but that they should not be replaced with refined carbohydrates.[34]

Heart-health organizations[edit]

Consumption of saturated fat is a risk factor for cardiovascular disease in the view of the Canadian Heart and Stroke Foundation,[35] the American Heart Association,[36] the British Heart Foundation,[6] the National Heart Foundation of Australia,[37] the National Heart Foundation of New Zealand [38] and the World Heart Federation.[7] The Irish Heart Foundation states that saturated fats can raise LDL cholesterol and increase the chance of developing heart disease.[39]

Governmental guidelines[edit]

The Dietary Guidelines for Americans, 2010 produced by the U.S. Department of Agriculture (USDA) and U.S. Department of Health and Human Services says the human body makes more than enough saturated fats to meet its needs and does not require more from dietary sources. It says higher levels of saturated fats are associated with higher levels of total cholesterol and low-density lipoprotein "bad" cholesterol and recommends reduced saturated fat intake.[40] The guidelines are based on the recommendations of the Dietary Guidelines Advisory Committee (DGAC) report that incorporated the results of the review of 12 studies from 2004 to 2009 conducted by the Nutrition Evidence Library (NEL) part of the Evidence Analysis Library Division of the USDA's Center for Nutrition Policy and Promotion. The NEL concluded that there was "strong" evidence that dietary saturated fats increased serum total cholesterol and LDL cholesterol and increased risk of cardiovascular disease.[41][42]

Editorial, commentary and conference findings[edit]

Recommendations for lower intake of saturated fat[edit]

A 2010 debate at the Academy of Nutrition and Dietetics's 93rd conference stated: "Regarding saturated fat, the key point agreed upon by the panel and scientific community at large was that researchers agree that replacing saturated fat with healthy polyunsaturated fats is beneficial for health and cardiovascular disease." Recommendations for dieticians emphasized using mono- and polyunsaturated fats whenever possible, avoiding trans fats. Further, "The evidence against saturated fat may not be as strong as dietary guidelines have interpreted [it is clear] that PUFAs (especially) and MUFAs are healthy fats", and that while there is room for saturated fats within the diet, but "[they] should not be viewed as good for you".[43]

A 2010 review found that the risk of coronary heart disease is reduced when saturated fatty acids are replaced with polyunsaturated fatty acids, but there was no clear benefit in replacing saturated fatty acids with carbohydrates or monounsaturated fatty acids.[44]

A 2009 review found that the best evidence showed reduced intake of saturated fat decreased the risk for coronary heart disease.[45]

Another 2009 review found that epidemiological evidence suggested a negative influence on vascular function from saturated fat, but that the experimental evidence did not support this convincingly.[46]

Opposition to reduced intake[edit]

A opinion critique of dietary guidelines which recommended lower intake of saturated fat summarized systematic reviews and meta-analyses that found insignificant effects on the incidence of cardiovascular diseases by reducing intake of saturated fat.[47]

The 2010 U.S. Dietary Guidelines Advisory Committee report was criticized for the "use of an incomplete body of relevant science; inaccurately representing, interpreting, or summarizing the literature; and drawing conclusions and/or making recommendations that do not reflect the limitations or controversies in the science" stating rather that the evidence associating dietary saturated fat with increased risk of cardiovascular disease is inconclusive.[48]

A 2010 meta-analysis concluded that no evidence exists that dietary saturated fat is associated with increased risk of cardiovascular diseases,[1] but this conclusion was disputed.[49]

A 2009 scientific conference reported that despite the contribution of dairy products to the saturated fatty acid intake of the diet, there was no clear evidence that dairy food consumption is consistently associated with a higher risk of cardiovascular disease.[50]

The Dairy Farmers of Canada published an opinion that summarized findings of a meta-analysis,[1] stating: "In light of new scientific data, it appears that saturated fat is not associated with an increased risk of cardiovascular disease."[51]

See also[edit]

References[edit]

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