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 Plenty of previous research has linked polyunsaturated fat in
vegetable oil, nuts and seeds with a lower risk of heart disease.
Based on these studies, people have been routinely advised to
replace animal fats like butter, cream and lard with plant-based
oils made from corn, soybean, canola and olives.
But this has never been proven by gold-standard studies that
randomly assigned people to specific diets to see how different
foods and fats impacted health and longevity, said Dr. Christopher
Ramsden, lead author of the current study.
When Ramsden’s team examined data from an experiment that did just
this with more than 9,400 people, they found the lower cholesterol
from swapping saturated fats for vegetable oils didn’t lead to
improved survival.
“In fact, participants who had greater reductions in cholesterol had
higher, rather than lower, risk of death,” Ramsden, a researcher at
the National Institutes of Health and the University of North
Carolina at Chapel Hill, said by email.
The researchers studied data from 1968 to 1973 on residents of one
nursing home and six mental hospitals in Minnesota, ranging in age
from 20 to 97.
Residents were randomly assigned to either a diet that replaced
saturated fat with corn oil and margarine made from corn oil, or to
a control group that ate meals high in saturated fat from animal
fats, common margarine and shortenings.
After switching to the vegetable oil diet, residents had a nearly 14
percent drop in cholesterol levels, compared with just a 1 percent
dip for the control group, researchers report in The BMJ, April 12.
But lower cholesterol didn’t turn out to be helpful.
Researchers looked at participants’ total serum cholesterol, which
includes triglycerides, LDL cholesterol and HDL cholesterol. The
American Heart Association says a total serum cholesterol of less
than 180 mg/dL is ideal.
For every 30 mg/dL reduction in cholesterol, however, people’s risk
of death rose 22 percent, based on an analysis of autopsy reports
available for the study population as of 2015.
In addition, the vegetable oil diet wasn’t tied to a reduced risk of
atherosclerosis.
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Limitations of the study include the fact that the experimental diet
included almost twice as much linoleic acid - the main
polyunsaturated fat in vegetable oil, nuts and seeds - as a typical
American diet.
Also, because the researchers used concentrated vegetable oils, the
findings might not apply to people who consume lots of linoleic acid
by eating nuts or seeds.
Even so, the findings suggest that saturated fat and linoleic acid,
one particular type of polyunsaturated fat, may not differ much in
their effects on vascular health, said Dr. Lennert Veerman, a public
health researcher at the University of Queensland in Australia who
wrote an editorial accompanying the study.
More research is still needed to fully understand which fats are
best, Veerman said by email.
“People should focus on recommendations that are not in doubt: avoid
trans fats, added sugars, and sodium, (and) eat a varied diet rich
in a variety of vegetables, whole fruits, whole grains, sea foods,
lean meats, eggs, legumes, and nuts, seeds and soy products,”
Veerman said.
As for vegetable oil, “it may or may not be better for blood vessels
compared to saturated fat, but there is no evidence that it does
harm and there is no need to stop using it,” Veerman added.
SOURCE: http://bit.ly/1sk4kGq
BMJ 2016.
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