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Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)

BMJ 2016; 353 doi: https://doi.org/10.1136/bmj.i1246 (Published 12 April 2016) Cite this as: BMJ 2016;353:i1246

Re: Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)

While the results of the RCTs clearly show that reducing serum cholesterol does not affect mortality, it is noteworthy that all of the RCTs cited by Ramsden et al. [1] were relatively short term, and many were conducted on middle-aged people, in whom we would expect to see significant atherosclerosis anyway.

In 1996, Uusitalo and coworkers [2] reported an interesting experiment in Mauritius. Because of concerns about the high rate of CHD, the government of Mauritius decided in 1987 to change the composition of the cooking oil produced by the one (government owned) factory in the country, from one based on palm oil (and hence high in saturated fatty acids) to one based on soy bean oil, and therefore high in poly-unsaturated fatty acids. Five years later (1992) there was the expected significant reduction in mean serum cholesterol, but no mention of CHD mortality. The WHO Noncommunicable Disease Country profile for Mauritius in 2014 [3] shows a significant fall in CHD mortality starting in 2003 and continuing to 2012 (the last year for which the data were available). Overall from 2003 to 2012 there was a 32% reduction in CHD mortality among men and 40% among women.

The 16 year time lag between the start of the intervention and the beginning of the decrease in CHD mortality can be explained. During the early years, older people with significant atherosclerosis, and therefore already at risk of death, did not benefit from the dietary change – it was too late for them. It was only as younger people, who had been exposed to the improved oil from early adulthood, reached middle age that there was evidence of benefit; they had accumulated less atherosclerotic plaque throughout their lives.

This highlights a key problem in research on the effects of diet on health – if we want to see survival and improved health into our 8th or 9th decade, we are looking at long-term (life-long) experiments. Obviously these cannot be RCTs or other intervention trials.

References
1) Ramsden CE et al. 2016. Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data form the Minnesota Coronary Experiment (1968-73). BMJ 353: i246. http: //dx.doi.org/bmj.i1246
2) Uusitalo U et al. 1996. Fall in total cholesterol concentration over five years in association with changes in fatty acid composition of cooking oil in Mauritius: cross sectional survey. BMJ 313: 1044-6.
3) WHO 2014. Noncommunicable Diseases (NCD) Country profiles. www.who.int/nmh/countries/mus_en.pdf

Competing interests: No competing interests

15 August 2017
David A Bender
Emeritus Professor of Nutritional. Biochemistry
University College London
Amersham