Health

Long-term dietary study suggests lower risk for unsaturated fats

Replacing trans fat and saturated fats such as red meat and butter with some plant-based foods offers health benefits, a large, long-term study suggests.

Fats in meat, dairy linked to higher risk of death in Harvard study

The study was observational and can't prove cause and effect. One complication is that people who eat less saturated fat might also be more health conscious in other ways. (Yiorgos Karahalis/Reuters)

Replacing trans fat and saturated fats from foods such as red meat and butter with some plant-based foods offers health benefits, say researchers who tracked diet patterns and deaths among more than 100,000 health professionals for up to three decades.

Amid competing low-fat diets and a trend back toward butter consumption, the evidence on how different dietary fats influence premature mortality has been unclear.

To try to clear up the confusion among the medical community and general public, Dr. Frank Hu, professor of nutrition and epidemiology at the Harvard T. H. Chan School of Public Health and his colleagues followed 126,233 female nurses and male health professionals in the U.S. Participants answered questionnaires about their diet, lifestyle and overall health every two to four years.

Over 32 years, 33,304 of the participants died, the researchers said in Tuesday's issue of the JAMA Internal Medicine.

Different types of fat had different associations with risk of death overall. For example, those who replaced saturated fats with unsaturated fats, especially polyunsaturated fats, had a significantly lower risk of death overall during the study period.

Their risk of death from cardiovascular disease, cancer, neurodegenerative disease and respiratory disease was lower than for those who continued to consume high amounts of saturated fats.

"These findings support current dietary recommendations to replace saturated fat and trans fat with unsaturated fats," the study's authors concluded.

For Canadians, mixed polyunsaturated fats are often consumed from fish such as salmon, trout and herring and to a lesser extent from plant sources such as walnuts, soybeans and canola oil, said Richard Bazinet, a professor in the department of nutritional sciences at the University of Toronto, who was not involved in the research.

Monounsaturated fats are found in olive oil, nuts and canola oil.

Confusing variables in dietary studies

The study was observational and can't prove cause and effect. Another complication is that people who eat less saturated fat might also be more health conscious in other ways, such as eating other nutritious foods or exercising, which can't be fully accounted for in the statistical models.  

"Part of the issue with these studies, and why I think some of the confusion comes is … they've tried to to reduce foods to the specific nutrients," Bazinet said. "If you take potato chips and you cook them in a highly polyunsaturated or unsaturated vegetable oil, the evidence doesn't really show they now become a good food choice."

Earlier this year, a published randomized trial, the gold standard type of medical research, challenged the idea that replacing saturated fat with corn oil lowers risk of coronary death.

What's the average eater to do?

"The monounsaturated fats look good in these studies. The polys containing omega-3s look good in most of these studies and that's where the focus should be," Bazinet suggested. "Go with what works."

The trans fats food manufacturers use to extend shelf life are being phased out, but people are still consuming too much, Health Canada says. The regulator adds that the same is true for saturated fats in red meat and dairy products that can increase the risk of developing heart disease.

With files from CBC's Amina Zafar

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