Dietary fat has come under fire in recent years, as study results have warned about links between certain sources of dietary fat and cardiovascular disease. The evidence on specific dietary fat and mortality, however, has been inconsistent. Now, a new study points to the health benefits of consuming more unsaturated fat.
The study, published in JAMA Internal Medicine, was led by researchers from the Harvard T.H. Chan School of Public Health in Boston, MA, including doctoral candidate Dong Wang.
According to the American Heart Association, saturated fat predominately comes from animal products, including beef, lamb, pork, butter, cream, cheese, and 2 percent milk. However, saturated fat can also come from plants, including coconut, coconut oil, palm oil, and cocoa butter.
Unsaturated fat - which includes polyunsaturated and monounsaturated fats - is found in fish such as salmon, trout, and herring, avocados, olives, walnuts, soybean oil, corn oil, safflower oil, canola oil, olive oil, and sunflower oil.
“There has been widespread confusion in the biomedical community and the general public in the last couple of years about the health effects of specific types of fat in the diet,” says Wang.
He adds that their study “documents important benefits of unsaturated fats, especially when they replace saturated and trans fats.”
Different types of dietary fat have different links with mortality: To carry out their study, the researchers followed 126,233 people for more than 30 years. The participants were part of two long-term studies: the Nurses’ Health Study and the Health Professionals Follow-Up Study.
During the course of the study period, the participants answered survey questions every 2-4 years regarding their diet, lifestyle, and overall health.
Over the course of 32 years, 33,304 of the participants died. The researchers investigated the link between fat type in the participants’ diets and overall deaths among the group. They also looked into deaths due to cardiovascular disease (CVD), cancer, neurodegenerative disease, and respiratory disease.
The team found that different types of dietary fat had different links with mortality. For every 2 percent higher intake of trans fat, there was a 16 percent higher chance of premature death.
Furthermore, higher saturated fat consumption was linked with greater mortality risk. The researchers found that, compared with the same number of calories fromcarbohydrates, each 5 percent saturated fat intake increase was linked with an 8 percent higher risk of mortality.
However, the team found that high intake of unsaturated fats - which included both polyunsaturated and monounsaturated fats - was linked with an 11-19 percent lower risk of mortality, compared with the same number of calories from carbohydrates.
In detail, both omega-6 fatty acids - found in most plant oils - and omega-3 fatty acids - found in fish, soy, and canola oils - were linked with a lower death risk.
Refined starches, sugars have similar mortality impact as saturated fats: The researchers note that the health effects they observed with specific types of fats depend on what they were replaced with. Study participants who replaced saturated fats with unsaturated fats had a much lower overall risk of death and a lower risk of death from CVD, cancer, neurodegenerative disease, and respiratory disease.
They also found that participants who replaced saturated fats with carbohydrates only had a slightly lower mortality risk.
Because carbohydrates in the American diet consist primarily of refined starch and sugar, the researchers say this finding was not a surprise; both refined starch and sugar have a similar impact on mortality risk as saturated fats.
The American Heart Association recommend that healthy people over the age of 2 eat 25-35 percent of their total daily calories as fats from foods such as fish, nuts, and vegetable oils.
They also recommend limiting saturated fats to less than 7 percent of total daily calories and limiting trans fats to less than 1 percent of total daily calories.
Meanwhile, they suggest that the majority of fats consumed should be either monounsaturated or polyunsaturated.