Eating unsaturated fats is associated with lower death risk, says a 30-year Harvard study

Food with unsaturated fats.
Food with unsaturated fats.

It is known that eating unsaturated fats is good to our health. These fats help reduce heart disease, lower cholesterol levels and have other health benefits when they replace saturated fats in the diet.

Now researchers from Harvard T.H. Chan School of Public Health show that eating higher amounts of unsaturated fats is associated with lower death risk.

The study is published in JAMA Internal Medicine.

The study included 126,233 participants from two large long-term studies—the Nurses’ Health Study and the Health Professionals Follow-Up Study—who answered survey questions every 2-4 years about their diet, lifestyle, and health for up to 32 years.

During the follow-up, 33,304 deaths were documented. Researchers examined the relationship between types of fats in the participants’ diets and overall deaths among the group during the study period.

The researchers found that different types of dietary fat had different associations with death.

Trans fats had the most significant negative impact on health. Every 2% higher intake of trans fat was associated with a 16% higher chance of premature death during the study period.

Higher consumption of saturated fats was also linked with greater death risk. When compared with the same number of calories from carbohydrate, every 5% increase in saturated fat intake was associated with an 8% higher risk of overall mortality.

Conversely, intake of high amounts of unsaturated fats was associated with between 11% and 19% lower overall mortality compared with the same number of calories from carbohydrates.

Among the unsaturated fats, both omega-6, found in most plant oils, and omega-3 fatty acids, found in fish and soy and canola oils, were associated with lower risk of premature death.

The health effects of specific types of fats depended on what people were replacing them with, the researchers found.

For example, people who replaced saturated fats with unsaturated fats had significantly lower risk of death overall during the study period, as well as lower risk of death from heart disease, cancer, neurodegenerative disease, and respiratory disease.

The findings for cardiovascular disease are consistent with many earlier studies showing reduced total and LDL (“bad”) cholesterol when unsaturated fats replace trans fats or saturated fats.

People who replaced saturated fats with carbohydrates had only slightly lower mortality risk. In addition, replacing total fat with carbohydrates was associated with modestly higher mortality.

This was not surprising, the authors said, because carbohydrates in the American diet tend to be primarily refined starch and sugar, which have a similar influence on mortality risk as saturated fats.

This study also provides further support for the 2015-2020 Dietary Guidelines for Americans that emphasize the types of fat rather than total amount of fat in the diet.

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Citation: Wang DD, et al. (2016). Specific Dietary Fats in Relation to Total and Cause-Specific Mortality. JAMA Internal Medicine, published online. DOI:10.1001/jamainternmed.2016.2417.
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