By Joseph E. Scherger, MD, MPH
Vice President, Primary Care, Eisenhower Medical Center; Clinical Professor, Keck School of Medicine, University of Southern California
SYNOPSIS: The NIH has been conducting systematic review and meta-analysis of randomized controlled trials show that replacing saturated fat with unsaturated vegetable oils rich in linoleic acid does not result in a reduction in atherosclerosis, cardiovascular morbidity, and death.
An NIH review and meta-analysis of randomized controlled studies determines that the replacement of saturated fat in a diet with unsaturated vegetable oils that are rich in linoleic acid does not reduce risk for atherosclerosis, cardiovascular diseases or death.
SOURCE: Ramsden CE, Daisy EZ, Majchirzak-Hong S, et al. Re-evaluation of the traditional diet-heart hypothesis: Analysis of recovered data from the Minnesota Coronary Experiment (1968-73). BMJ 2016;353:i1246.
It has long been suggested that the removal or substitution of saturated fat in a diet could aid in lowering risks of cardiovascular (CV) diseases. An investigative team from the National Institutes of Health conducted multiple systemic reviews and analyses of previous experimental data, both published and unpublished, that all tested the long-assumed dietary-cardio relationship between saturated fat and heart troubles. The traditional hypothesis is that the substitution of saturated fat with unsaturated fats and oils — particularly those high in linoleic acid — can lower a patient’s serum cholesterol. Drops in serum cholesterol were likewise traditionally considered to be linked to reduction of risk for CV diseases and CV-related death; however, the authors determined that no reliable, randomized studies have yet proven or even supported the hypothesis that substituting saturated fats with unsaturated fats and oils high in linoleic acid significantly alters or results in a reduction of a person’s risk for atherosclerosis or CV disease.
Of note is the Minnesota Coronary Experiment, conducted between 1968 and 1973. The nearly six-year study sampled patients from six state mental hospitals and one nursing home, randomizing 9,423 people aged 20-97, with a mean age of 52. Around one-fourth of the subjects involved in the study were 65 years or older. The regulation of food in the cafeterias at the institutions allowed for a more accurate assurance of adherence to dietary standards than the majority of population studies. Both groups ate similar fat amounts, and the groups’ average BMIs were similar. The control group’s diet was relatively unrestricted, while the intervention group saw a significant portion of the saturated fat in their diets substituted with corn oil products and corn oil polyunsaturated margarine. Following the completion of the study, detailed autopsy data were available for 149 of the tested subjects.
The intervention group, the patients that took in higher amounts of unsaturated fat saw significant lowering of both total and low-density lipoprotein cholesterol. Despite this, there was no significant difference among any age- or sex-matched cohort. In fact, the intervention group even experienced a higher rate of myocardial infarction. The autopsy reports available revealed that the rates of atherosclerosis among the groups were nearly identical.
These same authors have previously reported their re-analysis of the unpublished data from a large, randomized and controlled trial: The Sydney Diet Heart Study. Conducted during the same time as the Minnesota study, the Sydney study actually reported that the intervention group eating the diet with unsaturated fat (again, high in linoleic acid) substituted for saturated fat saw higher rates of both CV disease and CV mortality.