This study was published in the BMJ 2016 Apr 12;353:i1246
Study title and authors:
Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73).
Ramsden CE, Zamora D, Majchrzak-Hong S, Faurot KR, Broste SK, Frantz RP, Davis JM, Ringel A, Suchindran CM, Hibbeln JR.
USA Department of Physical Medicine and Rehabilitation, Program on Integrative Medicine, University of North Carolina, Chapel Hill, NC, USA
Chris.Ramsden@nih.gov.
This study can be accessed at: http://www.ncbi.nlm.nih.gov/pubmed/27071971
The objective of this study was to review the findings (by analysing unpublished "recovered" data from the original study investigators) of the Minnesota Coronary Experiment. The Minnesota Coronary Experiment was a double blinded, parallel group, randomized controlled dietary intervention trial conducted between 1968 - 1973, and was to designed to prove that increasing the polyunsaturated fat, (linoleic acid), and decreasing saturated fat in the diet would reduce cardiovascular events and deaths. It was the largest (9,570 participants, aged 20-97 years) and perhaps the most rigorously executed dietary trial of cholesterol lowering by replacement of saturated fat with vegetable oil rich in linoleic acid.
In the study participants were recruited from mental hospitals or nursing homes in the Minnesota area. They were divided into two groups:
(1) The intervention diet group had their dietary saturated fat cut in half (from 18.5% to 9.2% of calories) and their polyunsaturated linoleic fat intake massively increased from 3.4% to 13.2% of calories (a 280% increase).
(2) The control diet group did not change their saturated fat intake but did increase polyunsaturated linoleic acid intake from 3.4% to 4.7% of calories.
The "recovered" data, included previously unpublished records of serum cholesterol and autopsy reports and an extensive collection of study documents.
Using the "recovered" data the study found:
(i) The intervention group had significant reduction in cholesterol levels of 13.8%.
(ii) The control group had a small reduction in cholesterol levels of 1%.
(iii) A 30 mg/dL (0.78 mmol/L) decrease in cholesterol levels was associated with 22% higher risk of death from any cause.
(iv) Autopsy reports showed that participants in the intervention diet group had a 90% increased risk of a heart attack compared to participants in the control diet group.
The researchers also did a systematic review of the scientific literature and identified five randomized controlled trials that provided vegetable oil(s) rich in linoleic acid in place of saturated fat. These five trials included 10,808 participants. The average change in cholesterol levels in the course of the randomized controlled trials ranged from 7.8% to 13.8% lower in the intervention versus control groups.
The review of the five trials found:
(v) Those in the (low cholesterol) intervention groups had a 13% increased risk of death from coronary heart disease compared to those in the higher cholesterol control groups.
(vi) Those in the (low cholesterol) intervention groups had a 7% increased risk of death from all causes compared to those in the higher cholesterol control groups.
The above investigators also "recovered" unpublished data from the Sydney Diet Heart Study (1966-73) where the results of the trial was not fully reported. Ramsden commented: "Our recovery and 2013 publication of previously unpublished data from the Sydney Diet Heart Study (SDHS, 1966-73) belatedly showed that replacement of saturated fat with vegetable oil rich in linoleic acid significantly increased the risks of death from coronary heart disease and all causes, despite lowering serum cholesterol."
Critical points arise from this study:
(1) Key findings from landmark randomized controlled trials including the Sydney Diet Heart Study and the Minnesota Coronary Experiment were not fully published.
(2) Participants who had greater reductions in cholesterol levels had a higher, rather than lower, risk of death.
The question must be asked: "Why did the original investigators suppress this information?"
Is it because the results of the studies were clearly at odds with their beliefs?
Ramsden concluded: "It is interesting to speculate whether complete publication of randomized controlled trial results might have altered key policy decisions promoting replacement of saturated fat with linoleic acid rich oils (such as the 1977 McGovern report and National Cholesterol Education Program (1984-85) or contributed to a shift in research priorities."