Pamela A. Popper, Ph.D., N.D.

Wellness Forum Health

 One very popular theory of diet and heart health is that substituting saturated fat with “better fats” such as oils high in linoleic acid reduces cholesterol and lowers the risk and incidence of cardiovascular events and deaths. It’s a widely-held view, but there is not even one randomized controlled trial that has shown that replacing saturated fat with linoleic acid-rich oils is effective for these purposes.[1] In fact, studies have shown the opposite.

The Sydney Diet Heart Study showed that replacing saturated fat with high linoleic vegetable oil lowered cholesterol, but the risk of death from coronary heart disease and all-cause mortality increased.[2]  Recently the researchers who conducted this study decided to review previously unpublished data from the Minnesota Coronary Experiment (MCE) in order to investigate the issue further.[3]

MCE was the largest randomized controlled trial that looked at the effect of replacing saturated fat with vegetable oils for patients in hospitals, mental institutions and nursing homes. For the new review, researchers looked at raw MCE data which included serum cholesterol levels and autopsy reports. Additionally, they conducted a meta-analysis of some randomized controlled trials that looked at whether replacing saturated fat with vegetable oils resulted in reduced risk of death from coronary artery disease and all-cause mortality.

At baseline the hospital diet was comprised of 18.5% of calories from saturated fat and 3.8% of calories from polyunsaturated fat, for a total of 22.3% of calories from fat.

Liquid corn oil was used in place of regularly-used cooking fats such as hydrogenated oils; corn oil was added to foods like salad dressings, ground beef, and cheese; and polyunsaturated margarine was used instead of butter. Saturated fat intake decreased by about 50% (reduced from average 18.5% to 9.2% of calories) and linoleic acid intake increased from 3.4% to 13.2% of calories. The changes resulted in a diet with 22.4% of calories from fat. In other words, fat intake remained essentially the same.

Control patients did not reduce their intake of saturated fat but did increase their intake of linoleic acid slightly, from an average of 3.4% to 4.7% of calories. The control patients ate a diet that also included high intake of trans fatty acids

Intervention patients showed significantly lower plasma cholesterol levels than controls. More compliance, defined as fewer missed meals, was associated with even lower cholesterol levels. But these lower cholesterol levels did not translate to a decreased risk of death; in fact the mortality rate was higher for the group eating more linoleic acid than for the control patients. And there was a strong association between decreasing cholesterol levels and increased risk of death. Patients in the intervention group had almost twice as many heart attacks as those in the control group and for every 30 mg/dL drop in cholesterol, the risk of death increased by 35%.

The meta-analysis resulted in the same conclusion – consuming vegetables oils high in linoleic acid in place of saturated fat reduced cholesterol but did not reduce mortality rates.

Researcher Daisy Zamora says, “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.”[4]

This research confirms what I have been saying for many years – adopting a different version of a bad diet does not improve health.

Some people are interpreting this study to mean that eating butter and saturated fat is superior to eating vegetable oils, or that lowering cholesterol is not a good idea because it increases the death rate from heart disease. However, this is not true, and represents an incorrect analysis of the data.

In this study, both groups were eating a poor diet at the beginning of the study and continued to do so during the study. Omega-6 fatty acids (linoleic acid) are found in vegetable oils, nuts, seeds and animal products. The ratio of omega-3 to omega-6 fatty acids has changed considerably during the last few decades. It used to be between 1:1 and 1:4, and now ranges from 1:25 to as high as 1:50. This change is a contributing factor to increased incidence of many conditions, including heart disease. Therefore, decreasing intake of omega-6 fatty acids, by reducing intake of animal foods and polyunsaturated oils can lower the risk of coronary artery disease.

But in the case, the amount of omega-6 in the diet did not change, only the source did.  Corn oil replaced saturated fat. The intervention group reduced saturated fat intake by about 50% and increased linoleic acid intake by more than 280%. As a result the percentage of calories from fat in the diet remained essentially the same, only the source of the dietary fat changed.The intervention group consumed a terrible diet comprised of different types of fat.

In the meta-analysis, selection criteria excluded trials that involved higher intake of omega-3 fatty acids (which would have adjusted the ratio) and was limited to studies in which the only intervention was substitution of one type of omega-6 fat for another. So it is no surprising that the meta-analysis confirmed the findings for the MCE analysis. Substituting large amounts of polyunsaturated oils for saturated fat does not improve health outcomes.

I’m amazed that this research is getting so much attention from those who promote a diet high in animal foods and who claim that plasma cholesterol does not matter and that lower plasma levels result in worse health outcomes because the study design is so poor. The researchers acknowledged this and listed several limitations. The study subjects were different – patients in hospitals, mental institutions and nursing homes – which makes the results not necessarily applicable to members of the general population. Follow-up time was short – patients were only followed while in the hospital and only 25% of the patients were followed for a year or longer. The relationship between cholesterol and death rates from heart disease and all-cause mortality were only evaluated for those patients who were sick enough to remain in the hospital for an entire year. Numerous confounding factors would include medications taken and reasons for hospitalization were not considered. The researchers were not able to determine if the effects of corn oil were mitigated by smoking status, pre-existing coronary artery disease, psychiatric history, or drug use.

Intervention patients ate almost two times the amount of linoleic as the general population, which meant the intervention patients were eating diet worse than the general public. The group also cautioned that consuming concentrated vegetable oils is not the same as eating unprocessed foods like nuts that contain linoleic acid.

The meta-analysis included only observational studies and therefore, by their own admission, the researchers were unable to report a cause and effect relationship, and could not differentiate changes in serum cholesterol from diet vs from other causes.

In spite of these limitations, the study confirms what many other studies have shown – substituting one type of fat for another does not change health outcomes.[5] [6] Furthermore, research shows that all methods of lowering cholesterol do not result in better outcomes.  For example, statins drugs and supplements lower cholesterol, but do not significantly reduce the risk of events and death.[7] [8]

Patients are not visiting doctors because they are interested in better blood tests. What they are looking for is a better and longer life. The best way to achieve these goals is by adopting a low-fat, plant-based diet, which leads to better blood tests AND better health.

[1] Ramsden C, Zamora D, Majchrzak S et al. “Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from the Minnesota Coronary Experiment (1968-1973) BMJ 2016;353:i1246

[2] Ramsden C, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ 2013;346:e8707.

[3] Ramsden C, Zamora D, Majchrzak S et al. “Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from the Minnesota Coronary Experiment (1968-1973) BMJ 2016;353:i1246

[4] Niamh Michail “Switching from saturated fat to vegetable oils cuts cholesterol but increases heart attack risk: Review.”  Food Navigator April 13, 2016

[5] Blankenhorn, D.H. et al, “The Influence of Diet on the Appearance of New Lesions in Human Coronary Arteries.” JAMA March 23, 1990. 263(12):1646-1652

[6] Rudel L, Parks J, Sawyer J.  “Compared with Dietary Monounsaturated and Saturated Fat, Polyunsaturated Fat Protects African Green Monkeys from Coronary Artery Arteriosclerosis.” Arteriosclerosis Thrombosis and Vascular Biology (Impact Factor: 6). 01/1996; 15(12):2101-10. DOI: 10.1161/01.ATV.15.12.2101