An old study on saturated fat may throw conventional wisdom on its head.
More than 40 years ago, researchers conducted a dietary study among a large group of patients. Known as the Minnesota Coronary Experiment, the controlled trial aimed to show that removing saturated fat from people’s diets and replacing it with polyunsaturated fat from vegetable oils would protect them from heart disease and improve their mortality rates.
One group of patients was fed a diet intended to lower blood cholesterol and reduce heart disease by lowering saturated fat and adding more vegetable oil. The patients in the control ate a diet that included margarine and shortenings commonly used in the 1960s which were rich in trans fat.
The findings of the study, which was funded by the National Heart, Lung and Blood Institute, were never analyzed – until now.
Data reveals no benefit in subbing vegetable fats for saturated fats
A review of the raw data from the original Minnesota study was just published in the British Medical Journal. Researchers found that interventions using vegetable oils high in linoleic acids reduced blood cholesterol but did not reduce heart disease or overall mortality. In fact, participants in the Minnesota study who saw the greatest reduction in cholesterol had an even higher risk of death than their peers.
The researchers concluded: “ Minnesota Coronary Experiment findings add to growing evidence that incomplete publication has contributed to overestimation of benefits, and underestimation of potential risks, of replacing saturated fat with vegetable oils rich in linoleic acid.”
Corn oil, safflower oil, soybean oil, sunflower oil and cottonseed oil are all rich in linoleic acid, also known as omega-6 fatty acids.
Dr. John Pasquini , a cardiologist with Novant Health Heart & Vascular Institute in Charlotte, said that while the study provides valuable information, much of it is probably outdated. “At the time, the trial was state of the art, but it is really old now and it doesn’t incorporate much of the knowledge that we have gained about diet,” he said.
Pasquini cited several flaws with the study, including a large dropout rate among participants, the duration of the follow-up as, well as the amount of corn oil that was used in the study diet, which is more than double the amount that would be recommended today.
“The other problem was that omega-3 fatty acids were not even incorporated into the study and we know that omega-3s are very important in terms of protecting blood vessels.” Omega-3 fatty acids are found in flaxseed and canola oil, and in cold-water fish, such as salmon, cod and trout.
“The study tested the hypothesis that substituting vegetable fat for saturated fat would result in fewer strokes and heart attacks,” he said. “The study did not demonstrate a benefit of substituting vegetable fats for saturated fats.”
What works in the fight for heart health
In his daily practice, Pasquini recommends that patients with vascular disease and those interested in preventing the condition eat minimally processed foods and stay away from packaged or canned foods. “The type of diet for which the most data exist in terms of benefit to the heart is the Mediterranean diet,” he said. “I recommend a diet that is higher in fruits, vegetables, nuts, fish, olive oil and, if the person enjoys alcohol, one glass of wine a day for women and two for men – but limit the drinks to that amount.”
Pasquini said researchers continue to investigate which diet provides the best benefit in heart health to the most people. “We know that atherosclerosis, or hardening of the arteries, causes strokes, heart attacks, kidney failure and gangrene. It’s extremely common in our society and is mostly related to lifestyle factors such as diet, exercise and stress,” he said.
“These things we can change. Genetics play a small role in the development of atherosclerosis. It’s a lifestyle disease,” Pasquini said.
In terms of exercise, Pasquini recommends a half-hour to an hour per day of what he calls “sustainable exercise” – such as walking, swimming, jogging, bicycling or using an elliptical machine. The trick, he said, is to find something you enjoy.
People can also benefit from weight training 10 to 15 minutes a day, three days a week, to maintain muscle mass, he said.
Studies have shown that stress plays a big role in atherosclerosis, too, but is often underemphasized, according to Pasquini. Unfortunately, stress is hard to measure. “Managing stress is the key thing in life because we can’t avoid it and we can’t eliminate it,” he said.
Pasquini is optimistic, saying he believes that people can cure atherosclerosis if they are disciplined and consistent in managing lifestyle factors. “Since that study was done 45 years ago, there’s been a 60 percent reduction in the death rate from arthrosclerosis. That’s due to a number of factors, including diet, but it’s a huge drop in the mortality rate. We’ve done some things right, but we have a way to go.”