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.
Eating more foods with unsaturated fats - such as salmon, avocados, and
walnuts - is linked to a lower risk of death, researchers say.
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
from carbohydrates,
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.
"Our study shows the importance
of eliminating trans fat and replacing saturated fat with unsaturated fats,
including both omega-6 and omega-3 polyunsaturated fatty acids. In practice,
this can be achieved by replacing animal fats with a variety of liquid
vegetable oils."
Prof. Frank
Hu, senior author, Harvard Medical School
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.
Written
by Marie
Ellis
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