four-decades-old study — recently discovered in a dusty basement — has
raised new questions about longstanding dietary advice and the perils of
saturated fat in the American diet.
research, known as the Minnesota Coronary Experiment, was a major
controlled clinical trial conducted from 1968 to 1973, which studied the
diets of more than 9,000 people at state mental hospitals and a nursing
study, which was paid for by the National Heart, Lung and Blood
Institute and led by Dr. Ivan Frantz Jr. of the University of Minnesota
Medical School, researchers were able to tightly regulate the diets of
the institutionalized study subjects. Half of those subjects were fed
meals rich in saturated fats from milk, cheese and beef. The remaining
group ate a diet in which much of the saturated fat was removed and
replaced with corn oil, an unsaturated fat that is common in many
processed foods today. The study was intended to show that removing
saturated fat from people’s diets and replacing it with polyunsaturated
fat from vegetable oils would protect them against heart disease and
lower their mortality.
what was the result? Despite being one of the largest controlled
clinical dietary trials of its kind ever conducted, the data were never
years ago, Christopher E. Ramsden, a medical investigator at the
National Institutes of Health, learned about the long-overlooked study.
Intrigued, he contacted the University of Minnesota in hopes of
reviewing the unpublished data. Dr. Frantz, who died in 2009, had been a
prominent scientist at the university, where he studied the link
between saturated fat and heart disease. One of his closest colleagues
was Ancel Keys, an influential scientist whose research in the 1950s
helped establish saturated fat as public health enemy No. 1, prompting
the federal government to recommend low-fat diets to the entire nation.
father definitely believed in reducing saturated fats, and I grew up
that way,” said Dr. Robert Frantz, the lead researcher’s son and a
cardiologist at the Mayo Clinic. “We followed a relatively low-fat diet
at home, and on Sundays or special occasions, we’d have bacon and eggs.”
younger Dr. Frantz made three trips to the family home, finally
discovering the dusty box marked “Minnesota Coronary Survey,” in his
father’s basement. He turned it over to Dr. Ramsden for analysis.
results were a surprise. Participants who ate a diet low in saturated
fat and enriched with corn oil reduced their cholesterol by an average
of 14 percent, compared with a change of just 1 percent in the control
group. But the low-saturated fat diet did not reduce mortality. In fact,
the study found that the greater the drop in cholesterol, the higher
the risk of death during the trial.
findings run counter to conventional dietary recommendations that
advise a diet low in saturated fat to decrease heart risk. Current dietary guidelines
call for Americans to replace saturated fat, which tends to raise
cholesterol, with vegetable oils and other polyunsaturated fats, which
it is unclear why the trial data had not previously been fully
analyzed, one possibility is that Dr. Frantz and his colleagues faced
resistance from medical journals at a time when questioning the link
between saturated fat and disease was deeply unpopular.
could be that they tried to publish all of their results but had a hard
time getting them published,” said Daisy Zamora, an author of the new
study and a research scientist at the University of North Carolina at
younger Dr. Frantz said his father was probably startled by what seemed
to be no benefit in replacing saturated fat with vegetable oil.
it turned out that it didn’t reduce risk, it was quite puzzling,” he
said. “And since it was effective in lowering cholesterol, it was
The new analysis, published on Tuesday in the journal BMJ,
elicited a sharp response from top nutrition experts, who said the
study was flawed. Walter Willett, the chairman of the nutrition
department at the Harvard T.H. Chan School of Public Health, called the
research “irrelevant to current dietary recommendations” that emphasize
replacing saturated fat with polyunsaturated fat.
Hu, a nutrition expert who served on the government’s 2015 dietary
guidelines committee, said the Minnesota trial was not long enough to
show the cardiovascular benefits of consuming vegetable oil because the
patients on average were followed for only about 15 months. He pointed
to a major 2010 meta-analysis
that found that people had fewer heart attacks when they increased
their intake of vegetable oils and other polyunsaturated fats over at
least four years.
“I don’t think the authors’ strong conclusions are supported by the data,” he said.
investigate whether the new findings were a fluke, Dr. Zamora and her
colleagues analyzed four similar, rigorous trials that tested the
effects of replacing saturated fat with vegetable oils rich in linoleic
acid. Those, too, failed to show any reduction in mortality from heart
expect that the more you lowered cholesterol, the better the outcome,”
Dr. Ramsden said. “But in this case the opposite association was found.
The greater degree of cholesterol-lowering was associated with a higher,
rather than a lower, risk of death.”
explanation for the surprise finding may be omega-6 fatty acids, which
are found in high levels in corn, soybean, cottonseed and sunflower
oils. While leading nutrition experts point to ample evidence
that cooking with these vegetable oils instead of butter improves
cholesterol and prevents heart disease, others argue that high levels of
omega-6 can simultaneously promote inflammation. This inflammation
could outweigh the benefits of cholesterol reduction, they say.
2013, Dr. Ramsden and his colleagues published a controversial paper
about a large clinical trial that had been carried out in Australia in
the 1960s but had never been fully analyzed. The trial found that men
who replaced saturated fat with omega-6-rich polyunsaturated fats
lowered their cholesterol. But they were also more likely to die from a heart attack than a control group of men who ate more saturated fat.
Krauss, the former chairman of the American Heart Association’s dietary
guidelines committee, said the new research was intriguing. But he said
there was a vast body of research supporting polyunsaturated fats for
heart health, and that the relationship between cholesterol-lowering and
mortality could be deceiving.
who have high LDL cholesterol, the so-called bad kind, typically
experience greater drops in cholesterol in response to dietary changes
than people with lower LDL. Perhaps people in the new study who had the
greatest drop in cholesterol also had higher mortality rates because
they had more underlying disease.
possible that the greater cholesterol response was in people who had
more vascular risk related to their higher cholesterol levels,” he said.
Ramsden stressed that the team’s findings should be interpreted
cautiously. The research does not show that saturated fats are
beneficial, he said: “But maybe they’re not as bad as people thought.”
research underscores that the science behind dietary fat may be more
complex than nutrition recommendations suggest. The body requires
omega-6 fats like linoleic acid in small amounts. But emerging research
suggests that in excess linoleic acid may play a role in a variety of
disorders including liver disease and chronic pain.
century ago, it was common for Americans to get about 2 percent of
their daily calories from linoleic acid. Today, Americans on average
consume more than triple that amount, much of it from processed foods
like lunch meats, salad dressings, desserts, pizza, french fries and
packaged snacks like potato chips. More natural sources of fat such as
olive oil, butter and egg yolks contain linoleic acid as well but in smaller quantities.
Eating whole, unprocessed foods and plants may be one way to get all the linoleic acid your body needs, Dr. Ramsden said.
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