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Saturated fat and cardiovascular disease

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Whether saturated fat is a risk factor for cardiovascular disease (CVD) is a question with numerous controversial views.[1] Although there is a scientific consensus in the heart-health and medical communities that saturated fat is a risk factor for CVD, individual studies produce conflicting results and notable authors have given opposing viewpoints. The following sections are presented in descending order of reliability for medical sources.

Secondary sources

Systematic reviews in reputable medical journals

A 2010 systematic review and meta-analysis of randomized controlled trials commissioned by the National Heart, Lung, and Blood Institute found that substitution of poly-unsaturated fat for saturated fat led to a 19% reduction in Coronary Heart Disease.[2] The American Dietetic Association's 2008 systematic review found that a diet with 25%-35% total fat but less than 7% saturated fat and trans fat lowers the risk of coronary heart disease.[3] A 1999 review found that substitution of the fat from one ounce of nuts for equivalent energy from saturated fat was associated with a 45% reduction in risk of coronary heart disease.[4]

In 2009, a systematic review of prospective cohort studies or randomized trials concluded that there was "insufficient evidence of association" between intake of saturated fatty acids and coronary heart disease, and pointed to strong evidence for protective factors such as vegetables and a Mediterranean diet and harmful factors such as trans fats and foods with a high glycemic index.[5] However, this systematic review included studies that adjusted for serum lipids or other dietary lipids which were also included in the previously described meta-analysis.[1][5] A 2009 meta-analysis of cohort studies and randomized controlled trials from the University of Otago, New Zealand, found that the results of the cohort studies showed no association between coronary heart disease mortality nor total coronary heart disease events when saturated fat was increased in place of carbohydrates. In the randomized controlled trials where the ratio of polyunsaturated fat to saturated fat had been increased, the risk of coronary heart disease fatality was not changed, but the risk of total coronary heart disease events was decreased. The analysis was critical of the limitations of the primary evidence available, considering the evidence from cohort studies to be mostly unreliable.[6]

Some meta-analyses have found a significant relationship between saturated fat and serum cholesterol levels,[7][8] and serum cholesterol levels and cardiovascular disease,[9] yet 11 of the 15 studies that measured the relationship between saturated fat and coronary heart disease in this meta-analysis were adjusted for serum lipids or other dietary lipids. The remaining 4 studies found a significant relationship between saturated fat and coronary heart disease.[10] Furthermore, a positive relationship between saturated fat and fatal coronary heart disease was found despite an over-adjustment for serum lipids.[10]

In 2010, a meta-analysis of prospective cohort studies supported by the National Dairy Council including 348,000 subjects found no statistically significant relationship between cardiovascular disease and dietary saturated fat.[1][11]

A 2006 meta-analysis of prevention dietetic studies found the benefit of a modified fat diet in primary prevention is potentially significant if it is maintained for a sufficient length of time.[12]

A 2008 pooled analysis of 11 cohort studies supported by the National Heart, Lung, and Blood Institute, National Institutes of Health, the Danish Heart Foundation and the Danish Medical Research Council found that substituting polyunsaturated fatty acids in place of saturated fatty acids at a rate of 5% of energy intake led to 13% decrease in coronary events and a 26% decrease in coronary deaths.[13]

Specialist/professional textbooks

Position statements and guidelines of major health organizations

Medical establishments

The World Health Organization (WHO) has concluded that saturated fats negatively affect cholesterol profiles, predisposing individuals to heart disease, and recommends avoiding saturated fats in order to reduce the risk of a cardiovascular disease.[14][15][16]

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.[17]

Mayo Clinic highlighted oils that are high in saturated fats include coconut, palm oil and palm kernel oil. Those of lower amounts of saturated fats, and higher levels of unsaturated (preferably monounsaturated) fats like olive oil, peanut oil, canola oil, avocados, safflower, corn, sunflower, soy and cottonseed oils are generally healthier.[18]

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.[19]

Heart-health organizations

Consumption of saturated fat is a risk factor for cardiovascular disease in the view of the Canadian Heart and Stroke Foundation,[20] the American Heart Association,[21] the British Heart Foundation,[22] the National Heart Foundation of Australia,[23] the National Heart Foundation of New Zealand [24] and the World Heart Federation.[25] The Irish Heart Foundation states that saturated fats can raise your LDL cholesterol and increase your chances of getting heart disease.[26]

Governmental guidelines

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.[27] 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.[28][29]

Primary sources

Studies in reputable medical journals

Studies of dietary customs of certain ethnic groups may be confounded by other cultural customs. For example, Fulani of northern Nigeria get around 25% of energy from saturated fat, yet their lipid profile is indicative of a low risk of cardiovascular disease. However, this finding may be due to their high activity level and their low total energy intake.[30]

An evaluation of data from Harvard Nurses' Health Study found that "diets lower in carbohydrate and higher in protein and fat are not associated with increased risk of coronary heart disease in women. When vegetable sources of fat and protein are chosen, these diets may moderately reduce the risk of coronary heart disease."[31]

Pacific island populations who obtain 30-60% of their total caloric intake from fully saturated coconut fat have low rates of cardiovascular disease.[32]

A study published in the Lancet in 1994 found that how long-term dietary intake of essential fatty acids affects the fatty-acid content of aortic plaques is not clear.[33]

Tertiary sources

Editorial, commentary and conference findings in reputable medical journals

A 2010 perspective in the American Journal of Clinical Nutrition found that the risk of Coronary Heart Disease is reduced when saturated fatty acids are replaced with polyunsaturated fatty acids but no clear benefit in replacing saturated fatty acids with carbohydrates or monounsaturated fatty acids.[34]

In a special article in Nutrition led by the University of North Carolina at Chapel Hill, the 2010 Dietary Guidelines Advisory Committee (DGAC) 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 SFA with increased risk of CVD is inconclusive.[35]

A 2009 review from the University of Sao Paolo found that the best evidence showed reduced intake of saturated fat decreased risk for coronary heart disease.[36] A 2009 review from King's College London found that epidemiological evidence suggested a negative influence on vascular function from saturated fat, but that the experimental evidence did not support this convincingly.[37]

A 2004 commentary from the Nestle Research Center stated that no randomized clinical trials of low-fat diets or low-saturated fat diets of sufficient duration had been carried out. The influence of varying saturated fatty acid intakes against a background of different individual lifestyles and genetic backgrounds were recommended as the focus in future studies.[38] Saturated fat intakes may be monitored more closely than were total fat intakes, therefore ignoring the possibility that simply a larger fat intake may lead to a higher risk of coronary diseases. It also suggests that other parameters may be overlooked, such as carbohydrates intakes.[39] A scientific conference hosted by the University of Reading (UK) and organized and facilitated by the International Dairy Federation’s Standing Committee on Nutrition and Health found that despite the contribution of dairy products to the saturated fatty acid intake of the diet, there was not clear evidence that dairy food consumption is consistently associated with a higher risk of CVD.[40]

Lay scientific books

Gary Taubes, a science writer specializing in controversy and three-time winner of the Science in Society Award of the National Association of Science Writers concludes "Dietary fat, whether saturated or not, is not a cause of obesity, heart disease, or any other chronic disease of civilization."[41][42]

Writing in Men's Health Magazine, Nina Teicholz proposed that intake of saturated fat is only correlated with heart disease, "not a clear, causal link." [43]

Self-published works

Mary G. Enig a biochemist and nutritionist who is a member of the International Network of Cholesterol Skeptics states there is strong evidence for the cardiovascular benefits of saturated fats.[44]

See also

References

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  2. ^ Mozaffarian D, Micha R, Wallace S (2010). "Effects on Coronary Heart Disease of Increasing Polyunsaturated Fat in Place of Saturated Fat: A Systematic Review and Meta-Analysis of Randomized Controlled Trials". PLoS Medicine. 7 (3): 1–10. doi:10.1371/journal.pmed.1000252. ISSN 1549-1277. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
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  11. ^ Siri-Tarino PW, Sun Q, Hu FB, Krauss RM (2010). "Saturated fat, carbohydrate, and cardiovascular disease". The American Journal of Clinical Nutrition. 91 (3): 502–9. doi:10.3945/ajcn.2008.26285. PMC 2824150. PMID 20089734. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
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  13. ^ Jakobsen, MU; O'Reilly, EJ; Heitmann, BL; Pereira, MA; Bälter, K; Fraser, GE; Goldbourt, U; Hallmans, G; Knekt, P (2009). "Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies". The American journal of clinical nutrition. 89 (5): 1425–32. doi:10.3945/ajcn.2008.27124. PMC 2676998. PMID 19211817.
  14. ^ World Health Organization Risk factor: lipids
  15. ^ World Health Organization Prevention: personal choices and actions
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  18. ^ Dietary fats: Know which types to choose Mayo Clinic website
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  21. ^ American Heart Association. "Fat". Retrieved 2011-03-12.
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  34. ^ Astrup; et al. (2011). "The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: where does the evidence stand in 2010?". American Journal of Clinical Nutrition. doi:10.3945/ajcn.110.004622. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)
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  38. ^ German JB, Dillard CJ (2004). "Saturated fats: what dietary intake?". The American Journal of Clinical Nutrition. 80 (3): 550–9. PMID 15321792. {{cite journal}}: Unknown parameter |month= ignored (help)
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  40. ^ German JB, Gibson RA, Krauss RM; et al. (2009). "A reappraisal of the impact of dairy foods and milk fat on cardiovascular disease risk". European Journal of Nutrition. 48 (4): 191–203. doi:10.1007/s00394-009-0002-5. PMC 2695872. PMID 19259609. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  41. ^ Taubes, Gary (2007). Good Calories, Bad Calories. Knopf. p. 609. Retrieved 2011-01-02. {{cite book}}: Unknown parameter |Page= ignored (|page= suggested) (help)
  42. ^ Taubes, Gary. (July 7, 2002). What if It's All Been a Big Fat Lie?. The New York Times Magazine. Retrieved March 13, 2011.
  43. ^ Teicholz, Nina. (October 10, 2007). What if Bad Fat Is Actually Good for You?". Men's Health Magazine.
  44. ^ Fallon, Sally and Mary Enig. (1999). The Truth About Saturated Fats. Nourishing Traditions – The Cookbook that Challenges Politically Correct Nutrition and the Diet Dictocrats. NewTrends. ISBN 0967089735.

Further reading