Forty years ago, while the United States was preparing for the Bicentennial celebration, Minnesota researchers were studying the impact of dietary health guidelines and concluding that conventional wisdom on the subject might be wrong.
For whatever reason, the full results of the large-scale Minnesota Coronary Experiment were never published – until the medical journal BMJ did so April 12, 2016.
The researchers fed one group of subjects a diet with reduced saturated fat and cholesterol, but more vegetable oil, with the intent of lowering cholesterol and reducing heart disease. The other subjects were fed a more traditional diet.
While the diet did, as expected, reduce blood cholesterol levels, it didn’t impact heart disease and may have contributed to an increased number of deaths.
“Had this research been published 40 years ago, it might have changed the trajectory of diet-heart research and recommendations,” said Daisy Zamora, a researcher at the University of North Carolina and lead author of a new study that examined the Minnesota results.
The Washington Post noted that the government’s official diet advice book, “Dietary Guidelines for Americans,” still abides by the principles of a diet featuring less saturated fat and more vegetable oils.
“What this research implies is that there is not enough evidence to draw strong conclusions about the health effects of vegetable oils,” said Christopher Ramsden, a medical investigator at the National Institutes of Health, who indicated that saturated fats may not be as bad as originally thought.
Ramsden said the linoleic acid found in most vegetable oils may be linked to chronic pain, especially as Americans increase their oil consumption.
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Study opponents
Some experts say the study is faulty.
“The bottom line is that this report adds no useful new information and is irrelevant to current dietary recommendations that emphasize replacing saturated fat with polyunsaturated fat,” Dr. Walter Willett, chairman of the nutrition department at Harvard University, said in a blog post.
Willett noted that many test subjects were only on the diet for short periods. He said the original authors had intended to study the 9,423 subjects – institutionalized mental patients – for at least three years, but about 75% were discharged within a year.
Willett also said the study included linoleic acid levels well above American Heart Association recommendations and involved the creation of fake meat, cheese and milk that was made by removing fat and replacing it with corn oil.
Current federal dietary guidelines
Among other recommendations, “Dietary Guidelines for Americans,” calls for the use of oils from both plants and nuts, according to the federal Department of Health & Human Services (HHS). Americans are advised to consume about five teaspoons per day of oils.
It also recommends consuming less than 10% of calories daily from saturated fats.
“Foods that are high in saturated fat include butter, whole milk, meats that are not labeled as lean and tropical oils, such as coconut and palm oil,” the report said.
