Precious Yet Perilous
Written by Chris Masterjohn Phd
Vegetable Oils and Heart Disease : A Closer Look
Six randomized, controlled trials specifically testing the effect of the substitution of polyunsaturated vegetable oils for animal fats on heart disease have been published.64-69
The first randomized, controlled trial of dietary fat substitution was published in 1965. Substitution of corn oil for animal fat and carbohydrate doubled the number of major cardiac events. The results were not quite statistically significant, meaning there was a slight possibility they were due to chance. The researchers concluded “that under the circumstances of this trial corn oil cannot be recommended as a treatment of ischaemic heart disease. It is most unlikely to be beneficial, and it is possibly harmful.”64
A second trial found that replacing animal fats with polyunsaturated vegetable oils increased mortality by 39 percent. Rather than considering the possibility that the lipid hypothesis might be false, the investigators concluded that “men who have had myocardial infarction are not a good choice for testing the lipid hypothesis.”66
Three other such trials found either no effect,65, 67 or a small increase in mortality in the group consuming vegetable oil, which was not statistically significant.68
The longest study on the effect of vegetable oil ever conducted was the Wadsworth Veterans Administration Hospital Study.69 The researchers randomized over four hundred men who were long-term inpatients to one of two dining halls. One hall used butter and the other used a mix of vegetable oils. The study was double-blinded and lasted over eight years. The researchers took care not to reuse the vegetable oil after cooking but took no such precautions with the butter, resulting in butter that was very deficient in vitamin E.74 There were also twice as many heavy smokers and 60 percent more moderate smokers in the butter group. The group consuming butter had 50 percent more cardiovascular deaths. The group consuming vegetable oil, however, had more atherosclerosis than the control group and in the last few years of the study began experiencing a marked increase in the risk of cancer. Total mortality was slightly higher among those consuming vegetable oil, but the difference was not statistically significant.
There are two remarkable findings about this study. Even though cardiovascular deaths were lower in the vegetable oil group, atherosclerosis slightly increased. This clearly disproves the hypothesis that vegetable oils decrease the accumulation of atherosclerotic plaque by decreasing cholesterol levels. It further suggests that had there been an equal distribution of smokers between groups and had the control group received adequate vitamin E, vegetable oil may have proven to markedly increase the accumulation of atherosclerotic plaque as well as the risk of cardiovascular mortality. The fact that cancer began rising in the vegetable oil group in the last few years of the study—again, despite the heavy rate of smoking and deficient intake of vitamin E in the control group—suggests that the full extent of the ravages of oxidative stress and inflammation caused by vegetable oils takes at least five years to develop. A longer study may have shown a much greater risk of mortality in the vegetable oil group. These six studies clearly show that vegetable oils are not capable of reducing total mortality and strongly suggest that they may raise the risk of heart disease and cancer.