The science behind the recommended
change to vegetable oils about 50 years ago appears to be very faulty
and even the trail itself was not that great. The research suggests
that the switch from animal to vegetable (corn) fats may be not only
unnecessary, but it may misguided. Studies have arrived at similar
findings before, but the new one, which looks at the heart health of
people eating animal fats vs. corn oil, suggests that people who use
the latter may actually be at an increased heart risk.
The team looked at data from a study
that started in the late 60s, using 9,400 residents from several
mental hospitals and one nursing home (the participants coming from
these two communities may be a problem in itself). It wasn’t
published until 1989, for reasons that aren’t very clear, and it
reported that switching from animal fats to corn oil was beneficial
for cholesterol; it did not report that the switch had any effect on
heart disease.
A team at the NIH, the University of
North Carolina and several other universities uncovered the entire
data set and ran the stats again, because some had been omitted. The
reconsidered results were strange: People who ate vegetable oils had
lower cholesterol, but also had a significantly higher risk of heart
attack.
Though the research authors would not
say this, it looks like the previous researchers were cherry picking
data to arrive at the conclusion desired at the time. “Altogether,
this research leads us to conclude that incomplete publication of
important data has contributed to the overestimation of benefits–and
the underestimation of potential risks of replacing saturated fat
with vegetable oils rich in linoleic acid,” said Daisy Zamora.
The omega-6 fatty acid linoleic acid
(LA) is known to have some major health drawbacks. “An odd thing
about this is the outdated substitution of linoleic acid for
unspecified saturated fat,” says David L. Katz, founder of the Yale
Prevention Research Center. “Linoleic acid is an omega-6, and it’s
clear now that there are many problems associated with excessive
omega-6, notably interference with the production of long-chain
omega-3s.”
The two types of fats need to be
consumed into the body in balance, otherwise omega-6s usurp the
machinery needed to make omega-3s. But researchers have been aware
of this danger for some time. Omega-6 has also been linked to
increasing, rather than decreasing, inflammation.
Sunflower oil in the US was ‘upgraded’
through selective breeding to produce a high-oleic-acid variety (high
monounsaturated fatty acid) that now prevails, and avoids the
potential harms noted in this paper. The same thing is now being
done to soybean oil, and the high monounsaturated fatty acid version
of that will soon replace the old variety.”
So the new study may simply underline
that swapping animals fat for corn oil may lead to more health
problems than it solves. And as Katz points out, no one today would
think that making the swap the study made is terribly informative.
The evidence that replacing saturated
fat in general with a balanced portfolio of unsaturated fats from a
variety of foods is still questionable. The Dietary Guidelines
advise, oils from whole foods: nuts, seeds, avocado, fish. These do
not provide the excess of omega-6 likely in this case. Different
varieties of imbalance tend to represent different ways of eating
badly. The body needs, and responds well to, balance.”
For possible clarification of the
unnamed studies and more information, please read this blog by Dr.
Malcolm Kendrick. He does name the studies and makes the discussion
clearer.
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