Is Everything You Know About Healthy Eating Wrong?

You’ve probably put saturated fat on your list of deadly dietary sins. We’ve long been told that it increases our levels of “bad” LDL cholesterol, putting us at risk for deadly heart disease. But could an unanalysed study conducted more than 40 years ago have challenged our current views on saturated fat’s mortality risk?

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That’s the question some have been asking after a reevaluation of data taken from the Minnesota Coronary Experiment was published Tuesday in the BMJ. Christopher Ramsden, a medical investigator at the National Institutes of Health, heard about the Minnesota Coronary Experiment (MCE) a few years back during his hunt to study the effect of linoleic acid, found in seed oils, on the body. The MCE’s controlled clinical trial involved more than 9,000 men and women from state mental hospitals and a nursing home.

Between 1968 and 1973, researchers fed half of the participants diets high in saturated fats found in milk, cheese, and other animal products. The remaining men and women were given diets nearly devoid of saturated fat, with corn oil in its place. Corn oil is an unsaturated fat found in a lot of the processed snack foods on store shelves today.

The researchers aimed to show that the polyunsaturated fats found in vegetable oils would help ward off heart disease and lead to lower mortality rates. However, as Ramsden discovered, the full results of the study were never revealed. He reached out to the University of Minnesota to see if he could access this information.

Although lead study author Ivan Frantz Jr. had since passed away, his son, Mayo Clinic cardiologist Robert Frantz, found data from the Minnesota Coronary Experiment hidden in a box in the basement of the family home, which he sent over to Ramsden for a second look.

“My father definitely believed in reducing saturated fats, and I grew up that way,” the junior Frantz told the Times. “We followed a relatively low-fat diet at home, and on Sundays or special occasions, we’d have bacon and eggs.”

Interestingly, the old results went against common current wisdom about fat. Although participants that ate the diet low in saturated fats — with corn oil as a substitute — dropped their cholesterol levels by around 14 percent, they did not see a lower risk of death. The study actually showed that the greater the cholesterol reduction, the higher risk of mortality during the trial period.

The golden rule on fat consumption — which has been increasingly under question — is to keep your diet low in saturated fats to help reduce your risk of cardiovascular disease, replacing them with polyunsaturated fats found in vegetable oils like the corn oil used in the Minnesota Coronary Experiment.

The New York Times poses several reasons the full results of the study never made front-page news. Perhaps there was pushback from the dietary community and medical journals about the results, which would have likely been met with frowns and groans during a time when everything was “low-fat” and “no-fat.”

There’s also a chance that Ivan Frantz didn’t know what to make of results that showed lower cholesterol levels without lower mortality. However, it’s possible that those with higher “bad” LDL cholesterol levels would be more affected by dietary changes and may have had greater levels of disease to account for the higher mortality.

The study authors believe that we should be questioning the impact of reduced saturated fat. “Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid,” they wrote in the study.

According to study co-lead researcher Daisy Zamora, a researcher at the University of North Carolina School of Medicine, we might be wise to take a deeper look at linoleic acid. “In addition to the MCE, we also did a meta-analysis on other, similar trials,” she tells Yahoo Beauty. “There wasn’t a benefit of replacing saturated fats on mortality from heart disease or any other cause. It does make you wonder.”

Fat might be an even more complicated beast than we realise. Zamora and Ramsden think the linoleic acid found in substances like seed oils (corn, safflower, sunflower, soybean) may be a bigger culprit contributing to adverse health effects.

Zamora says that we do need small amounts of this polyunsaturated fat, but perhaps not as much as we’re consuming now. “Around 200 years ago, a normal American diet would derive less than three percent of calories from linoleic acid,” she explains. “Today, it’s seven percent. That’s a big jump, considering that it’s a bioactive compound. It can be oxidised. It’s converted into biochemical mediators that seem to act like hormones to direct processes in the body, but of which very little is known.”

As for saturated fat? That’s interesting, says Zamora. This experiment focused on the replacement of saturated fat, not on saturated fat alone. But since the spike in blood cholesterol is a key reason many experts believe saturated fat is bad for you, it’s unclear if it’s directly related to conditions like heart disease and higher mortality. “More research is needed,” she suggests.

Rebecca Blake, RD, a dietitian and the administrative director of medicine at Mount Sinai Beth Israel, cautions against abandoning current wisdom on saturated fats due to this new analysis. “We are looking at an institutionalised population, and the potential confounding variables are not clear,” she tells Yahoo Beauty.

Fat might be an even more complicated beast than we realize. Zamora and Ramsden think the linoleic acid found in substances like seed oils (corn, safflower, sunflower, soybean) may be a bigger culprit contributing to adverse health effects.

Zamora says that we do need small amounts of this polyunsaturated fat, but perhaps not as much as we’re consuming now. “Around 200 years ago, a normal diet would derive less than three percent of calories from linoleic acid,” she explains. “Today, it’s seven percent. That’s a big jump, considering that it’s a bioactive compound. It can be oxidized. It’s converted into biochemical mediators that seem to act like hormones to direct processes in the body, but of which very little is known.”

As for saturated fat? That’s interesting, says Zamora. This experiment focused on the replacement of saturated fat, not on saturated fat alone. But since the spike in blood cholesterol is a key reason many experts believe saturated fat is bad for you, it’s unclear if it’s directly related to conditions like heart disease and higher mortality. “More research is needed,” she suggests.

Rebecca Blake, RD, a dietitian and the administrative director of medicine at Mount Sinai Beth Israel, cautions against abandoning current wisdom on saturated fats due to this new analysis. “We are looking at an institutionalised population, and the potential confounding variables are not clear,” she tells Yahoo Beauty.

Since the study indicates that margarine made from hydrogenated corn oil was a major sources of the polyunsaturated fats used, she suspects there may have been another reason for the lowered cholesterol levels and higher mortality rate.

“A hydrogenated fat source is a trans fat, which we now know to be incredibly detrimental to heart health,” Blake says. “It is quite possible that the group that had reduced saturated fat intake and increased polyunsaturated fat intake actually had extremely high trans fat intake — which could explain the higher risk of death.”

However, like Zamora, Blake does believe there’s enough evidence to warrant further investigation of saturated fat’s effect on mortality. However, “the recommendation is still to keep saturated fat intake to a minimum, or no more than 120 calories or 17 grams derived from saturated fat daily if you are consuming about 2,000 calories per day,” she explains.

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Blake says obesity is an enormous risk factor when it comes to cardiac and endocrine problems, so it’s smart to start by eating a well-rounded diet and maintaining a healthy body weight.