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Analysis: Replacing saturated fat with linoleic acid may not confer mortality benefit
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In an analysis of unpublished data from a nearly 50-year-old study, researchers found that a diet replacing saturated fat with linoleic acid did not affect all-cause mortality.
“This research leads us to conclude that incomplete publication of important data has contributed to the overestimation of benefits — and the underestimation of potential risks — of replacing saturated fat with vegetable oils rich in linoleic acid,” Daisy Zamora, PhD, researcher in the department of psychiatry at the University of North Carolina School of Medicine, Chapel Hill, said in a press release.
The Minnesota Coronary Experiment was a double blind, randomized controlled trial of 9,423 participants from one nursing home and six mental hospitals in Minnesota who were assigned a control diet high in saturated fat from animal fats, margarines and shortenings or a cholesterol-lowering diet replacing saturated fats with linoleic acid from corn oil and corn oil polyunsaturated margarine. Outcomes of interest included all-cause death, relationship between change in cholesterol level and death, coronary atherosclerosis and MI.
Initial findings published in 1989 indicated that the cholesterol-lowering diet lowered cholesterol levels but did not affect MI, death from MI or all-cause mortality.
According to the release, the researchers for the present study discovered that planned analyses from the Minnesota Coronary Experiment were never published. They recovered raw data, including autopsy reports, and unpublished analyses. Based on those, they performed their own analyses of the Minnesota Coronary Experiment data and incorporated those findings into a meta-analysis of randomized controlled trials of cholesterol-lowering interventions.
Lower cholesterol
Zamora and colleagues found that the intervention group from the Minnesota Coronary Experiment had a greater reduction in serum cholesterol compared with controls (–13.8% vs. –1%; P < .001), there was no mortality benefit from the intervention in the overall cohort, men, women, those younger than 65 years or those aged at least 65 years.
After adjustment, the researchers found an elevated risk for death for each 30 mg/dL reduction in serum cholesterol (HR = 1.22; 95% CI, 1.14-1.32). This was most pronounced in people aged at least 65 years (adjusted HR = 1.35; 95% CI, 1.19-1.53).
There was no significant difference between the groups in coronary atherosclerosis score (P = .059) or aortic atherosclerosis score (P = .223).
The researchers also found that, among those for whom autopsy reports were available (76 from intervention group; 73 from control group), 41% of those in the intervention group had at least one MI vs. 22% in the control group (incidence rate ratio = 1.9; 95% CI, 1.01-3.72); and that there was no association between serum cholesterol and MI.
In the meta-analysis of 10,808 participants from five trials including the Minnesota Coronary Experiment, Zamora and colleagues found no association between cholesterol-lowering interventions and CHD mortality (HR = 1.13; 95% CI, 0.83-1.54) or all-cause mortality (HR = 1.07; 95% CI, 0.9-1.27).
Irrelevant to current recommendations
In a letter to the editor, Walter C. Willett, MD, DrPH, Fredrick John Stare Professor of Epidemiology and Nutrition and chair of the department of nutrition at Harvard T.H. Chan School of Public Health, wrote, “This report adds no useful new information and is irrelevant to current dietary recommendations that emphasize overall dietary patterns and replacing saturated fat with polyunsaturated fat, including sources of both [omega]-3 and [omega]-6 fatty acids.
“The diet used in the Minnesota trial was never consumed by any appreciable number of Americans and is not recommended by the American Heart Association or any group” and that “even in its time, the Minnesota trial, conducted among patients in mental hospitals, was a major failure due to the massive dropouts and very short duration on the assigned diets,” Willett wrote. – by Erik Swain
Disclosure: The researchers and Willett report no relevant financial disclosures.
Perspective
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Robert H. Eckel, MD
The evidence for restriction of saturated fats and lowering of LDL is convincing. Our American College of Cardiology/AHA Guideline on Lifestyle Management to Reduce CV Risk documents this benefit (Eckel RH, et al. Circulation. 2013;doi:10.1161/01.cir.0000437740.48606.d1) and the practice of preventive cardiology should not change based on the present analysis.
The benefits of linoleic acid vs. saturated fats were summed up well by Farvid and colleagues (Farvid MS, et al. Circulation. 2014;doi: 10.1161/CIRCULATIONAHA.114.010236.) They concluded: “In prospective observational studies, dietary [linoleic acid] intake is inversely associated with CHD risk in a dose-response manner. These data provide support for current recommendations to replace saturated fat with polyunsaturated fat for primary prevention of CHD.” Other research has indicated that the optimal intake of saturated fats is 5% to 6% of calories.
Randomized controlled trials of lifestyle and outcomes such as CVD events and mortality are difficult to implement and interpret. In practice, we work to reduce risk including LDL, BP, glucose and beyond. We should rely on the evidence on how to do this best and hopefully outcomes will be favorable.
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