New Study Challenges Consensus on Link Between Dietary Fat, Heart Disease

Barbara Hollingsworth | May 4, 2016 | 2:16pm EDT
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Corn oil. (Wikipedia)

( –  A new study has challenged the scientific consensus that replacing saturated fats with polyunsaturated vegetable oils rich in linoleic acid (omega-6) reduces the risk of death from coronary heart disease.

Every five years, the federal government publishes nutritional guidelines that “reflect the current body of nutrition science” and “serve as the foundation for vital nutrition policies and programs across the United States.”

The 2015-2020 Dietary Guidelines’ recommendation to “limit intake of calories from saturated fats to less than 10 percent per day is a target based on evidence that replacing saturated fats with unsaturated fats is associated with reduced risk of cardiovascular disease.” 

According to the Centers for Disease Control (CDC), “diets high in saturated fats, trans fat, and cholesterol have been linked to heart disease and related conditions, such as atherosclerosis.”

But the study, which was published April 12 in the British Medical Journal (BMJ), found that “replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol, but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes.”

“As expected, the diet enriched with linoleic acid lowered cholesterol levels, but this did not translate to improved survival,” according to a BMJ press release. “In fact, participants who had greater reduction in blood cholesterol had higher, rather than lower, risk of death.”

The study was conducted by a team of researchers from the U.S. and Australia led by Christopher Ramsden, a medical investigator at the National Institutes of Health, who reexamined raw data and unpublished autopsy reports from the federally funded Minnesota Coronary Experiment (MCE).

The MCE was “a randomized controlled trial conducted in 1968-73” of 9,423 individuals between the ages of 20 and 97 who were living in six state mental hospitals and a nursing home in Minnesota.

Study participants who were assigned to the control diet for more than a year had a high intake of saturated fats from milk, cheese and beef.

However, the diet of the “intervention group” replaced about 50 percent of the saturated fat in the control diet with a 280 percent increase in polyunsaturated vegetable fat, mostly in the form of corn oil and corn oil margarine.

“Though the MCE intervention effectively lowered serum cholesterol in all pre-specified subgroups, there was no clinical benefit in any group. Paradoxically, MCE participants who had greater reduction in serum cholesterol had a higher rather than a lower risk of death,” the study found.  

“In addition, the MCE intervention group did not have less atherosclerosis or fewer infarcts at autopsy.”

Autopsy results showed that “41% (31/76) of participants in the intervention group had at least one myocardial infarct, whereas only 22% (16/73) of participants in the control group did,” according to the research team.

“There was a robust association between decreasing serum cholesterol and increased risk of death, and this association did not differ between the intervention and control group,” the study noted.

“This finding that greater lowering of serum cholesterol was associated with a higher rather than a lower risk of death in the MCE does not provide support for the traditional diet-heart hypothesis,” the researchers concluded.

The same research team also reported that after conducting a meta-analysis of the Sydney Diet Heart Study on the use of lineolic acid to prevent coronary heart disease in 2013, they also found that the “intervention group had an increased risk of death from coronary heart disease and all causes, despite a significant reduction in serum cholesterol.”

“The benefits of choosing polyunsaturated fat over saturated fat seem a little less certain than we thought,” Lennert Veerman, senior lecturer at the University of Queensland School of Public Health, wrote in a BJM editorial commenting on the study.

A 2014 study published in the Annals of Internal Medicine also concluded that "current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats."

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