Expert answer:Methodological problems in Dr. Keys nutrition rese
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The Questionable Link Between Saturated Fat and Heart Disease
By
Nina Teicholz and Gary Taubes
(1) If the members of the American medical establishment were to have a collective findyourself-standing-naked-in-Times-Square-type nightmare, this might be it. They spend 30 years
ridiculing Robert Atkins, author of the phenomenally-best-selling ”Dr. Atkins’ Diet Revolution”
and ”Dr. Atkins’ New Diet Revolution,” accusing the Manhattan doctor of quackery and fraud,
only to discover that the unrepentant Atkins was right all along. Or maybe it’s this: they find that
their very own dietary recommendations — eat less fat and more carbohydrates — are the cause of
the rampaging epidemic of obesity in America. Or, just possibly this: they find out both of the
above are true.
(2) When Atkins first published his ”Diet Revolution” in 1972, Americans were just
coming to terms with the proposition that fat – particularly the saturated fat of meat and dairy
products — was the primary nutritional evil in the American diet. Atkins managed to sell millions
of copies of a book promising that we would lose weight eating steak, eggs and butter to our
heart’s desire, because it was the carbohydrates, the pasta, rice, bagels and sugar that caused
obesity and even heart disease. Fat, he said, was harmless. Atkins banned even fruit juices, and
permitted only a modicum of vegetables, although the latter were negotiable as the diet
progressed.
(4) Forty years later, America has become weirdly polarized on the subject of weight. On
the one hand, we’ve been told with almost religious certainty by everyone from the surgeon
general on down, and we have come to believe with almost religious certainty, that obesity is
caused by the excessive consumption of fat, and that if we eat less fat we will lose weight and
live longer. On the other, we have the ever-resilient message of Atkins and decades’ worth of
best-selling diet books, including ”The Zone,” ”Sugar Busters” and ”Protein Power” to name a
few. All push some variation of what scientists would call the alternative hypothesis: it’s not the
fat that makes us fat, but the carbohydrates, and if we eat fewer carbohydrates we will lose
weight and live longer.
(5) The perversity of this alternative thinking is that it identifies the cause of obesity as
precisely those refined carbohydrates at the base of the famous Food Guide Pyramid — the pasta,
rice and bread — that we are told should be the staple of our healthy low-fat diet, and then on the
sugar or corn syrup in the soft drinks, fruit juices and sports drinks that we have taken to
consuming in quantity if for no other reason than that they are fat free and so appear intrinsically
healthy. While the low-fat-is-good-health dogma represents reality as we have come to know it,
and the government has spent hundreds of millions of dollars in research trying to prove its
worth, the low-carbohydrate message has been relegated to the realm of unscientific fantasy.
(5) Over the past fifteen years, however, there has been a subtle shift in the scientific
consensus. It used to be that even considering the possibility of the alternative hypothesis, let
alone researching it, was tantamount to quackery by association. Now a small but growing
minority of establishment researchers have come to take seriously what the low-carb-diet doctors
have been saying all along. Walter Willett, chairman of the department of nutrition at the
Harvard School of Public Health, may be the most visible proponent of testing this heretic
hypothesis. Willett is the de facto spokesman of the longest-running, most comprehensive diet
and health studies ever performed, which have already cost upward of $100 million and include
data on nearly 300,000 individuals. Those data, says Willett, clearly contradict the low-fat-is-
good-health message ”and the idea that all fat is bad for you; the exclusive focus on adverse
effects of fat may have contributed to the obesity epidemic.”
(6) “Saturated fat does not cause heart disease”—or so concluded a big study published
in March in the journal Annals of Internal Medicine. How could this be? The very cornerstone of
dietary advice for generations has been that the saturated fats in butter, cheese and red meat
should be avoided because they clog our arteries. For many diet-conscious Americans, it is
simply second nature to opt for chicken over sirloin, canola oil over butter. However, the new
study’s conclusion shouldn’t surprise anyone familiar with modern nutritional science. The fact
is, there has never been solid evidence for the idea that these fats cause disease. We only believe
this to be the case because nutrition policy has been derailed over the past half-century by a
mixture of personal ambition, bad science, politics and bias.
(7) Our distrust of saturated fat can be traced back to the 1950s, to a man named Ancel
Benjamin Keys, a scientist at the University of Minnesota. Dr. Keys was formidably persuasive
and, through sheer force of will, rose to the top of the nutrition world—even gracing the cover of
Time magazine—for relentlessly championing the idea that saturated fats raise cholesterol and,
as a result, cause heart attacks. This idea fell on receptive ears because, at the time, Americans
faced a fast-growing epidemic. Heart disease, a rarity only three decades earlier, had quickly
become the nation’s No. 1 killer. Even President Dwight D. Eisenhower suffered a heart attack in
1955. Researchers were desperate for answers. Consequently, as the director of the largest
nutrition study through the 1960s, Dr. Keys was in an excellent position to promote his idea. The
“Seven Countries” study that he conducted on nearly 13,000 men in the U.S., Japan and Europe
ostensibly demonstrated that heart disease wasn’t the inevitable result of aging but could be
linked to poor nutrition.
(8) Critics have pointed out that Dr. Keys violated several basic scientific norms in his
study. For one, he didn’t choose countries randomly but instead selected only those likely to
prove his beliefs, including Yugoslavia, Finland and Italy. Excluded were France, land of the
famously healthy omelet eater, as well as other countries where people consumed a lot of fat yet
didn’t suffer from high rates of heart disease, such as Switzerland, Sweden and West Germany.
The study’s star subjects—upon whom much of our current understanding of the Mediterranean
diet is based—were peasants from Crete, islanders who tilled their fields well into old age and
who appeared to eat very little meat or cheese.
(9) As it turns out, Dr. Keys visited Crete during an unrepresentative period of extreme
hardship after World War II. Furthermore, he made the mistake of measuring the islanders’ diet
partly during Lent, when they were forgoing meat and cheese. Dr. Keys therefore undercounted
their consumption of saturated fat. Also, due to problems with the surveys, he ended up relying
on data from just a few dozen men—far from the representative sample of 655 that he had
initially selected. These flaws weren’t revealed until much later, in a 2002 paper by scientists
investigating the work on Crete—but by then, the misimpression left by his erroneous data had
become international dogma.
(10) In 1961, Dr. Keys sealed saturated fat’s fate by landing a position on the nutrition
committee of the American Heart Association, whose dietary guidelines are considered the gold
standard. Although the committee had originally been skeptical of his hypothesis, it issued, in
that year, the country’s first-ever guidelines targeting saturated fats. The U.S. Department of
Agriculture followed in 1980.
(11) Other studies ensued. A half-dozen large, important trials pitted a diet high in
vegetable oil—usually corn or soybean, but not olive oil—against one with more animal fats. But
these trials, mainly from the 1970s, also had serious methodological problems. Some didn’t
control for smoking, for instance, or allowed men to wander in and out of the research group
over the course of the experiment. The results were unreliable at best. But there was no turning
back: Too much institutional energy and research money had already been spent trying to prove
Dr. Keys’s hypothesis. A bias in its favor had grown so strong that the idea just started to seem
like common sense. As Harvard nutrition professor Mark Hegsted said in 1977, after
successfully persuading the U.S. Senate to recommend Dr. Keys’s diet for the entire nation, the
question wasn’t whether Americans should change their diets, but why not? Important benefits
could be expected, he argued. And the risks? “None can be identified,” he said.
(12) In fact, even back then, other scientists were warning about the diet’s potential
unintended consequences. Today, we are dealing with the reality that these have come to pass.
One consequence is that in cutting back on fats, we are now eating a lot more carbohydrates—at
least 25% more since the early 1970s. Consumption of saturated fat, meanwhile, has dropped by
11%, according to the best available government data. Translation: Instead of meat, eggs and
cheese, we’re eating more pasta, grains, fruit and starchy vegetables such as potatoes. Even
seemingly healthy low-fat foods, such as yogurt, are stealth carb-delivery systems, since
removing the fat often requires the addition of fillers to make up for lost texture—and these are
usually carbohydrate-based.
(13) The problem is that carbohydrates break down into glucose, which causes the body
to release insulin—a hormone that is fantastically efficient at storing fat. Meanwhile, fructose,
the main sugar in fruit, causes the liver to generate triglycerides and other lipids in the blood that
are altogether bad news. Excessive carbohydrates lead not only to obesity but also, over time, to
Type 2 diabetes and, very likely, heart disease.
(14) The real surprise is that, according to the best science to date, people put themselves
at higher risk for these conditions no matter what kind of carbohydrates they eat. Yes, even
unrefined carbs. Too much whole-grain oatmeal for breakfast and whole-grain pasta for dinner,
with fruit snacks in between, add up to a less healthy diet than one of eggs and bacon, followed
by fish. The reality is that fat doesn’t make you fat or diabetic. Scientific investigations going
back to the 1950s suggest that actually, carbs do.
(15) The second big unintended consequence of our shift away from animal fats is that
we’re now consuming more vegetable oils. Butter and lard had long been staples of the American
pantry until Crisco, introduced in 1911, became the first vegetable-based fat to win wide
acceptance in U.S. kitchens. Then came margarines made from vegetable oil and then just plain
vegetable oil in bottles.
(16) All of these got a boost from the American Heart Association—which Procter &
Gamble, the maker of Crisco oil, coincidentally helped launch as a national organization. In
1948, P&G made the AHA the beneficiary of the popular “Walking Man” radio contest, which
the company sponsored. The show raised $1.7 million for the group and transformed it
(according to the AHA’s official history) from a small, underfunded professional society into the
powerhouse that it remains today.
(17) After the AHA advised the public to eat less saturated fat and switch to vegetable
oils for a “healthy heart” in 1961, Americans changed their diets. Now these oils represent 7% to
8% of all calories in our diet, up from nearly zero in 1900, the biggest increase in consumption of
any type of food over the past century.
(18) This shift seemed like a good idea at the time, but it brought many potential health
problems in its wake. In those early clinical trials, people on diets high in vegetable oil were
found to suffer higher rates not only of cancer but also of gallstones. And, strikingly, they were
more likely to die from violent accidents and suicides. Alarmed by these findings, the National
Institutes of Health convened researchers several times in the early 1980s to try to explain these
“side effects,” but they couldn’t. (Experts now speculate that certain psychological problems
might be related to changes in brain chemistry caused by diet, such as fatty-acid imbalances or
the depletion of cholesterol.)
(19) We’ve also known since the 1940s that when heated, vegetable oils create oxidation
products that, in experiments on animals, lead to cirrhosis of the liver and early death. For these
reasons, some midcentury chemists warned against the consumption of these oils, but their
concerns were allayed by a chemical fix: Oils could be rendered more stable through a process
called hydrogenation, which used a catalyst to turn them from oils into solids.
(20) From the 1950s on, these hardened oils became the backbone of the entire food
industry, used in cakes, cookies, chips, breads, frostings, fillings, and frozen and fried food.
Unfortunately, hydrogenation also produced trans fats, which since the 1970s have been
suspected of interfering with basic cellular functioning and were recently condemned by the
Food and Drug Administration for their ability to raise our levels of “bad” LDL cholesterol.
(21) Yet paradoxically, the drive to get rid of trans fats has led some restaurants and food
manufacturers to return to using regular liquid oils—with the same long-standing oxidation
problems. These dangers are especially acute in restaurant fryers, where the oils are heated to
high temperatures over long periods.
(22) The past decade of research on these oxidation products has produced a sizable body
of evidence showing their dramatic inflammatory and oxidative effects, which implicates them in
heart disease and other illnesses such as Alzheimer’s. Other newly discovered potential toxins in
vegetable oils, called monochloropropane diols and glycidol esters, are now causing concern
among health authorities in Europe.
(23) In short, the track record of vegetable oils is highly worrisome—and not remotely
what Americans bargained for when they gave up butter and lard. Cutting back on saturated fat
has had especially harmful consequences for women, who, due to hormonal differences, contract
heart disease later in life and in a way that is distinct from men. If anything, high total cholesterol
levels in women over 50 were found early on to be associated with longer life. This
counterintuitive result was first discovered by the famous Framingham study on heart-disease
risk factors in 1971 and has since been confirmed by other research.
(24) Since women under 50 rarely get heart disease, the implication is that women of all
ages have been worrying about their cholesterol levels needlessly. Yet the Framingham study’s
findings on women were omitted from the study’s conclusions. And less than a decade later,
government health officials pushed their advice about fat and cholesterol on all Americans over
age 2—based exclusively on data from middle-aged men.
(25) Sticking to these guidelines has meant ignoring growing evidence that women on
diets low in saturated fat actually increase their risk of having a heart attack. The “good” HDL
cholesterol drops precipitously for women on this diet (it drops for men too, but less so). The sad
irony is that women have been especially rigorous about ramping up on their fruits, vegetables
and grains, but they now suffer from higher obesity rates than men, and their death rates from
heart disease have reached parity.
(26) Seeing the U.S. population grow sicker and fatter while adhering to official dietary
guidelines has put nutrition authorities in an awkward position. Recently, the response of many
researchers has been to blame “Big Food” for bombarding Americans with sugar-laden products.
No doubt these are bad for us, but it is also fair to say that the food industry has simply been
responding to the dietary guidelines issued by the AHA and USDA, which have encouraged
high-carbohydrate diets and until quite recently said next to nothing about the need to limit
sugar.
(27) Indeed, up until 1999, the AHA was still advising Americans to reach for “soft
drinks,” and in 2001, the group was still recommending snacks of “gum-drops” and “hard
candies made primarily with sugar” to avoid fatty foods.
(28) Our half-century effort to cut back on the consumption of meat, eggs and whole-fat
dairy has a tragic quality. More than a billion dollars have been spent trying to prove Ancel
Keys’s hypothesis, but evidence of its benefits has never been produced. It is time to put the
saturated-fat hypothesis to bed and to move on to test other possible culprits for our nation’s
health woes.
…
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