This is Part 2 in the series which examines the enduring belief that dietary saturated fat causes heart disease.
INTRODUCTION: The “diet-heart hypothesis” is the belief that saturated fat and dietary cholesterol cause heart disease was first proposed by Ancel Keys in the 1950s. He encouraged Americans to reduce their fat intake by a third, while at the same time openly admitted as late as 1967 that there was little direct evidence that a change in diet would reduce the risks of arteriosclerosis . As covered in the first part of this article, three Harvard researchers, Stare, Hegsted and McGrady were paid generously by the sugar industry to publish their review in the New England Journal of Medicine vindicating sugar as a cause of heart disease and laying the blame squarely on dietary fat; and in particular on saturated fat. These researchers concluded that there was “only one avenue” by which diet contributed to the development and progression of “hardening of the arteries” (atherosclerosis), resulting heart disease and that was due to how much dietary cholesterol people ate and its effect on blood lipids . This sounds like a very certain claim, however it is known that they lacked evidence because a year later (1968) a report from the Diet-Heart Review Panel of the National Heart Institute made the recommendation that a major study be conducted to determine whether changes in dietary fat intake prevented heart disease – because such a study had not yet been done (see Part 1) .
Fast forward ten years and in 1977, one of the three researchers who was paid by the sugar industry, Dr. DM Hegsted contributed to and edited the 1977 US Dietary Guidelines , which embodied his findings 10 years earlier. Americans were told they should reduce their intake of saturated fat and cholesterol to reduce their risk of heart disease.
The rest, they say, is history.
The same year (1977), Canada’s Food Guide recommended that Canadians limit fat to <30% of daily calories with no more than 1/3 from saturated fat, but did not specify an upper limit for dietary cholesterol. This was based on the belief that total dietary fat and saturated fat were responsible blood levels of LDL cholesterol levels and total serum cholesterol, not dietary cholesterol .
Recommendations for the continued restriction of dietary fat continued in both the US and Canada in 2015 are based on the enduring belief that lowering saturated fat in the diet will lower blood cholesterol levels and reduce heart disease.
The question is does it?
NOTE TO CANADIANS: Canadian Dietary Recommendations regarding dietary intake of saturated fat are based on 'health claim assessments' conducted by Health Canada which are directly tied to American research and recommendations. Eighteen years ago, Health Canada reviewed the 'health claim' regarding Dietary Fat, Saturated Fat, Cholesterol, Trans Fats and Coronary Heart Disease and based on the US literature available from 1993-2000 and concluded that a health risk exists between saturated fat and heart disease, as stated here; "The effectiveness of lowering dietary saturated fat in reducing plasma cholesterol, especially low-density lipoprotein (LDL)- cholesterol, the major risk factor for CHD, is well established." Since Health Canada's review in 2000 (18 years ago), the link between dietary saturated fat and heart disease remains public health policy.
While it has been shown that saturated fats can raise LDL-cholesterol such a finding is meaningless unless it is specified which type of LDL-cholesterol goes up. There is more than one type of LDL-cholesterol, small, dense LDL cholesterol which easily penetrates the artery wall is associated with heart disease [6,7,8,9], whereas the large, fluffy LDL cholesterol is not [10, 11].
Another factor that needs to be considered is that dietary saturated fat also consistently raises the “good” HDL-cholesterol which moves cholesterol away from the arteries and back to the liver, where it can either be re-used or eliminated [12,13].
What are the findings of current scientific literature?
Eight recent meta-analysis and systemic reviews which reviewed evidence from randomized control trials (RCT) that had been conducted between 2009-2017 did not find an association between saturated fat intake and the risk of heart disease [14-21].
Furthermore, recently published results of the largest and most global epidemiological study published in December 2017 in The Lancet  found that those who ate the largest amount of saturated fats had significantly reduced rates of mortality and that low consumption (6-7% of calories) of saturated fat was associated with increased risk of stroke.
Here is a synopsis of the findings of the eight meta-analysis and systemic reviews;
“Intake of saturated fatty acids was not significantly associated with coronary heart disease mortality” and “saturated fatty acid intake was not significantly associated coronary heart disease events”
Skeaff CM, PhD, Professor, Dept. of Human Nutrition, the University of Otago, Miller J. Dietary Fat and Coronary Heart Disease: Summary of Evidence From Prospective Cohort and Randomised Controlled
“There were no clear effects of dietary fat changes on total mortality or cardiovascular mortality”.
Hooper L, Summerbell CD, Thompson R, Reduced or modified dietary fat for preventing cardiovascular disease, 2012 Cochrane Database Syst Rev. 2012 May 16;(5)
“Current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats.”
Chowdhury R, Warnakula S, Kunutsor S et al, Association of Dietary, Circulating, and Supplement Fatty Acids with Coronary Risk: A Systematic Review and Meta-analysis, Ann Intern Med. 2014 Mar 18;160(6):398-406
“The present systematic review provides no moderate quality evidence for the beneficial effects of reduced/modified fat diets in the secondary prevention of coronary heart disease. Recommending higher intakes of polyunsaturated fatty acids in replacement of saturated fatty acids was not associated with risk reduction.”
Schwingshackl L, Hoffmann G Dietary fatty acids in the secondary prevention of coronary heart disease: a systematic review, meta-analysis and meta-regression BMJ Open 2014;4
“The study found no statistically significant effects of reducing saturated fat on the following outcomes: all-cause mortality, cardiovascular mortality, fatal MIs (myocardial infarctions), non-fatal MIs, stroke, coronary heart disease mortality, coronary heart disease events.”
Note: The one significant finding was an effect for saturated fats on cardiovascular events however this finding lost significance when subjected to a sensitivity analysis (Table 8, page 137).
Hooper L, Martin N, Abdelhamid A et al, Reduction in saturated fat intake for cardiovascular disease, Cochrane Database Syst Rev. 2015 Jun 10;(6)
“Epidemiological evidence to date found no significant difference in CHD mortality and total fat or saturated fat intake and thus does not support the present dietary fat guidelines. The evidence per se lacks generalizability for population-wide guidelines.”
Harcombe Z, Baker JS, Davies B, Evidence from prospective cohort studies does not support current dietary fat guidelines: a systematic review and meta-analysis, Br J Sports Med. 2017 Dec;51(24):1743-1749
“Available evidence from randomized controlled trials (1968-1973) provides no indication of benefit on coronary heart disease or all-cause mortality from replacing saturated fat with linoleic acid rich vegetable oils (such as corn oil, sunflower oil, safflower oil, cottonseed oil, or soybean oil).”
Ramsden CE, Zamora D, Majchrzak-Hong S, et al, Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73), BMJ 2016; 353
“Available evidence from adequately controlled randomised controlled trials suggest replacing saturated fatty acids with mostly n-6 PUFA is unlikely to reduce coronary heart disease events, coronary heart disease mortality or total mortality. These findings have implications for current dietary recommendations.”
Hamley S, The effect of replacing saturated fat with mostly n-6 polyunsaturated fat on coronary heart disease: a meta-analysis of randomised controlled trials, Nutrition Journal 2017 16:30
Only one recent meta analysis conducted by the American Heart Association (by the authors of the Diet-Heart Policy for Americans, mentioned above) found a relationship between saturated fat intake and coronary heart disease, yet failed to examine cardiovascular mortality (death) or total mortality .
NOTE: In 1961, the American Heart Association was the author of the original policy paper recommending to limit saturated fats to protect against heart disease and therefore has a significant interest in defending its longtime institutional position.
With the exception of the American Heart Association review, the conclusion of 9 different meta-analysis and review papers of randomized control trials conducted by independent teams of scientists worldwide do not support the belief that dietary intake of saturated fat causes heart disease.
The PURE (Prospective Urban Rural Epidemiology) was the largest-ever epidemiological study and was published in The Lancet in December 2017 . It recorded dietary intake in 135,000 people in 18 countries over an average of 7 1/2 years, including high-, medium- and low-income nations. It found;
“High carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to lower total mortality. Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke. Global dietary guidelines should be reconsidered in light of these findings.”
Dehghan M, Mente A, Zhang X et al, The PURE Study – Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet. 2017 Nov 4;390(10107):2050-2062
Those critical of the study say that it has methodological problems, including problems related to the authors dividing consumption of macronutrients (protein, fat and carbohydrate) into 4 groups (quintiles). Some say that this is reason the data showed an inverse relationship between saturated fat and cardiovascular disease . Criticisms also include that one cannot compare data between countries of substantially different level of income because “low fat consumption is very uncommon in high income countries” and that ‘the ability to afford certain foods may change the dietary pattern (e.g. high-carbohydrate and low-fat diets may be associated with poverty) .
Both the American and Canadian governments are currently in the process of revising their Dietary Guidelines and I feel that what is needed now is an external, independent scientific review of the current evidence-base for the belief that saturated fat contributes to heart disease.
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- Keys A, Aravanis C, Blackburn HW et al. Epidemiological studies related to coronary heart disease: characteristics of men aged 40–59 in seven countries Acta Med Scand 1967 460: 1–392.
- McGandy, RB, Hegsted DM, Stare,FJ. Dietary fats, carbohydrates and atherosclerotic vascular disease. New England Journal of Medicine. 1967 Aug 03; 277(5):242–47
- The National Diet-Heart Study Final Report.” Circulation, 1968; 37(3 suppl): I1-I26. Report of the Diet-Heart Review Panel of the National Heart Institute. Mass Field Trials and the Diet-Heart Question: Their Significance, Timeliness, Feasibility and Applicability. Dallas, Tex: American Heart Association; 1969, AHA Monograph no. 28.
- Introduction to the Dietary Goals for the United States – by Dr D.M. Hegsted. Professor of Nutrition, Harvard School of Public Health, Boston, MASS., page 17 of 130, https://naldc.nal.usda.gov/naldc/download.xhtml?id=1759572&content=PDF
- McDonald BE, The Canadian experience: why Canada decided against an upper limit for cholesterol, J Am Coll Nutr. 2004 Dec;23(6 Suppl):616S-620S.
- Tribble DL, Holl LG, Wood PD, et al. Variations in oxidative susceptibility among six low density lipoprotein subfractions of differing density and particle size. Atherosclerosis 1992;93:189–99
- Gardner CD, Fortmann SP, Krauss RM, Association of Small Low-Density Lipoprotein Particles With the Incidence of Coronary Artery Disease in Men and Women, JAMA. 1996;276(11):875-881
- Lamarche B, Tchernof A, Moorjani S, et al, Small, Dense Low-Density Lipoprotein Particles as a Predictor of the Risk of Ischemic Heart Disease in Men,
- Packard C, Caslake M, Shepherd J. The role of small, dense low density lipoprotein (LDL): a new look, Int J of Cardiology, Volume 74, Supplement 1, 30 June 2000, Pages S17-S22
- Genest JJ, Blijlevens E, McNamara JR, Low density lipoprotein particle size and coronary artery disease, Arteriosclerosis, Thrombosis, and Vascular Biology. 1992;12:187-195
- Siri-Tarino PW, Sun Q, Hu FB, Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease, The American Journal of Clinical Nutrition, Volume 91, Issue 3, 1 March 2010, Pages 502–509
- Mensink RP, Zock PL, Kester A, Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials, The American Journal of Clinical Nutrition, Volume 77, Issue 5, 1 May 2003, Pages 1146–1155
- Toth PP, The “Good Cholesterol” – High Density Lipoprotein, Circulation 2005;111:e89-e91
- Skeaff CM, PhD, Professor, Dept. of Human Nutrition, the University of Otago, Miller J. Dietary Fat and Coronary Heart Disease: Summary of Evidence From Prospective Cohort and Randomised Controlled Trials, Annals of Nutrition and Metabolism, 2009;55(1-3):173-201
- Hooper L, Summerbell CD, Thompson R, Reduced or modified dietary fat for preventing cardiovascular disease, 2012 Cochrane Database Syst Rev. 2012 May 16;(5)
- Chowdhury R, Warnakula S, Kunutsor S et al, Association of Dietary, Circulating, and Supplement Fatty Acids with Coronary Risk: A Systematic Review and Meta-analysis, Ann Intern Med. 2014 Mar 18;160(6):398-406
- Schwingshackl L, Hoffmann G Dietary fatty acids in the secondary prevention of coronary heart disease: a systematic review, meta-analysis and meta-regression BMJ Open 2014;4
- Hooper L, Martin N, Abdelhamid A et al, Reduction in saturated fat intake for cardiovascular disease, Cochrane Database Syst Rev. 2015 Jun 10;(6)
- Harcombe Z, Baker JS, Davies B, Evidence from prospective cohort studies does not support current dietary fat guidelines: a systematic review and meta-analysis, Br J Sports Med. 2017 Dec;51(24):1743-1749
- Ramsden CE, Zamora D, Majchrzak-Hong S, et al, Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73), BMJ 2016; 353
- Hamley S, The effect of replacing saturated fat with mostly n-6 polyunsaturated fat on coronary heart disease: a meta-analysis of randomised controlled trials, Nutrition Journal 2017 16:30
- Sachs FM, Lichtenstein AH, Wu JHW et al, Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association, Circulation. 2017 Jul 18;136(3)
- Dehghan M, Mente A, Zhang X et al, The PURE Study – Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet. 2017 Nov 4;390(10107):2050-2062
- Sigurdsson, AF, The Fate of the PURE Study – Fat and Carbohydrate Intake Revisited, Doc’s Opinion, October 16 2017, www.docsopinion.com/2017/10/16/pure-study-fats-carbohydrates/
Note: References 11-23 were from a document prepared by the Nutrition Coalition
Special thanks to Dr. Carol Loffelmann and Dr. Barbra Allen Bradshaw of The Canadian Clinicians for Therapeutic Nutrition for their tireless research.
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