Just days after a group called the Nutrition Coalition cast dispersion on the government's dietary guidelines for its anti-fat mantra, a new article in the British Medical Journal reiterates the message.
In that article, a team of scientists at the University of North Carolina (UNC) School of Medicine and the National Institutes of Health cast doubt on the supposedly "heart-healthy" practice of replacing butter and other saturated fats with corn oil and other vegetable oils high in linoleic acid.
In fact, the findings suggest that using vegetable oils high in linoleic acid might be worse than using butter when it comes to preventing heart disease. This agrees with several other studies of recent years. An article in Feedstuffs asks Did butter get a bad rap?
This latest evidence comes from an analysis of previously unpublished data from a large controlled trial conducted in Minnesota nearly 50 years ago, as well as a broader analysis of published data from all similar trials of this dietary intervention.
The analyses show that interventions using vegetable oils high in linoleic acid failed to reduce heart disease and overall mortality, even though the intervention reduced cholesterol levels. In the Minnesota study, participants who had greater reduction in serum cholesterol had a higher rather than lower risk of death. This is another major problem with public perception that cholesterol is bad, created by government warnings to that effect.
"Altogether, 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," wrote co-first author Daisy Zamora, a researcher in the department of psychiatry at the UNC School of Medicine.
Along with corn oil, linoleic acid-rich oils include safflower, soybean, sunflower and cottonseed oils.
The belief that replacing saturated fats with vegetable oils improves heart health dates back to the 1960s, when studies began to show that this dietary switch lowered blood cholesterol levels. At the time, a small but vocal and politically influential group of researchers were pushing the idea that high cholesterol levels were tied to increased heart disease.
Although some epidemiological studies have suggested this is true, randomized controlled trials with large numbers of humans — considered the gold standard for medical research — have never shown that linoleic acid-based dietary interventions reduce the risk of heart attack or death.
The largest of these trials, the Minnesota Coronary Experiment (MCE), was conducted by researchers at the University of Minnesota between 1968 and 1973. It used 9,423 patients in six state mental hospitals and one state-run nursing home. Its results did not appear in a medical journal until 1989. The investigators reported then that a switch to corn oil from butter and other saturated fats did lower cholesterol levels but made no difference in terms of heart attacks, deaths due to heart attacks or overall deaths.
Of course, this old and unpublished study formed the basis for the new study. To read more, go to this story in Science Daily.