Re: Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)
The “International Expert Movement to improve dietary fat quality” (IEM) submits the following comments on “Re-evaluation of the Traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968- 1973)”
The topic of dietary fat intake is one of great interest and one of great confusion for consumers. A recent publication appears to be adding to that confusion. In the manuscript “Re-evaluation of the Traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968- 1973)” Ramsden et al reexamined data that is more than 40 years old. These data had not been previously used in the Minnesota Coronary Experiment (MCE), and by doing an updated meta-analysis, the authors attempted to determine if the original outcomes were in fact supported by current randomized controlled trials (RCTs). Unfortunately their conclusions are plagued with several limitations.
The Minnesota Coronary Experiment (MCE) had a more than 75% dropout rate after one year. This makes it difficult to determine real outcomes of diet change and disease due to the short study duration and the lack of statistical power to detect any effects of treatment on endpoints. Outcomes related to mortality were published in 1989 by Frantz, and were included in meta-analyses setting current dietary guidelines, but the original study did not report on associations between cholesterol and endpoints.1 In addition; the association between changes in blood cholesterol levels and death was observational, so the outcome, identical in both study diets, is really associative, not causal.
The overall dietary intake, along with trans fat intake, of subjects in the MCE was not assessed meaning that any study outcomes could be subject to other dietary factors, especially trans fat. Given the impact of trans fats on heart disease risk this failure to assess trans fat intakes makes the extrapolation of diet –outcome-relations of the MCE to current dietary patterns questionable. The MCE study also did not assess LDL cholesterol levels, weight loss, smoking status or presence of existing coronary disease – variables that can significantly affect outcomes - making any conclusion from the study open to question.
This new analysis also attempted to compare mortality outcomes from other RCT’s to the MCE and found 4 smaller RCT’s that studied replacement of saturated fats with linoleic rich vegetable oil. These studies did not all use mortality as an endpoint so comparing the outcomes of these trials was not reviewing comparable studies. In addition, because the MCE trial was the largest RCT in the meta-analysis conducted by Ramsden et al the MCE trial contributed the greatest weight to the results of the meta-analysis.
We note that many of the references used in this publication were out of date and/or not supportive of the statements that they were linked with. The current body of scientific evidence continues to support the importance of limiting saturated fat and replacing it with unsaturated fats, especially polyunsaturated fats, including but not limited to, the essential fatty acid linoleic acid.
The “2013 AHA/ACC Guideline on Lifestyle Management to Reduce Cardiovascular Risk A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines” 2 clearly reviewed the evidence supporting lowering saturated fats and choosing polyunsaturated fats instead as a means of lowering LDL-Cholesterol, thus reducing heart disease risk.
The 2015 US Dietary Guidelines Committee scientific report also addressed the topic of saturated fats and disease risk with a systematic review of both RCTs and observational studies and reported the following:
“Strong and consistent evidence from RCTs shows that replacing SFA with unsaturated fats, especially PUFA, significantly reduces total and LDL cholesterol.”
“Strong and consistent evidence from RCTs and statistical modeling in prospective cohort studies shows that replacing SFA with PUFA reduces the risk of CVD events and coronary mortality.”
“For every 1 percent of energy intake from SFA replaced with PUFA, incidence of CHD is reduced by 2 to 3 percent. However, reducing total fat (replacing total fat with overall
carbohydrates) does not lower CVD risk.” 3
Changing dietary habits is a challenging task for consumers. Studies that do not put their outcomes in context or do not draw conclusions that reflect a cause and effect outcome only contribute to the confusion. Ramsden et al have conducted a data analysis that can be viewed as adding to the body of evidence on the topic of fats and cardiovascular disease. However, the analysis does not provide evidence that indicates how to change dietary habits, and in our view only adds confusion to the topic of healthful fats.
1. Frantz, ID. Et al. Test of Effect of Lipid Lowering by Diet on Cardiovascular Risk. The Minnesota Coronary Survey. Atherosclerosis 1989; 9:129-135
2. Eckel, R. et al. AHA/ACC guideline on lifestyle management to reduce cardiovascular risk: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 2014 Jun 24;129(25 Suppl 2):S76-99.
doi: 10.1161/01.cir.0000437740.48606.d1. Epub 2013 Nov 12. 2013 .
3. Scientific Report of the 2015 Dietary Guidelines Advisory Committee. http://health.gov/dietaryguidelines/2015-scientific-report/pdfs/scientif.... Accessed April 20. 2016
Authors (IEM committee members)
Helmut Heseker, Professor. MD, PhD Institute of Nutrition, Consumption and Health
Faculty of Natural Sciences University Paderborn. IUNS Council Member
BERTHOLD V. KOLETZKO, Professor of Paediatrics. MD PhD (Dr med Dr med habil)
Head Div. Metabolic Diseases & Nutritional Medicine, Univ. Munich Medical Centre, Munich, Germany.
CONNIE DIEKMAN, MEd, RD, CSSD, LD, FAND
Director of University Nutrition at Washington University in St. Louis, Missouri.
GERARD HORNSTRA, PhD Med
Professor Em. of Experimental Nutrition, Maastricht University, Maastricht, The Netherlands
JOYCE NETTLETON, DSc; Specialist in seafood nutrition and science communication.
Dr Joyce Nettleton has an independent consulting practice, ScienceVoice Consulting, in Denver, CO.
Competing interests: No competing interests