Which vegetable oils are best
February 12th, 2017
by Gabe Mirkin, MD
Which Vegetable Oils Are Best?
For more than 65 years, doctors have told their patients
that they could lower blood cholesterol levels and
prevent heart attacks and premature death by
substituting polyunsaturated fats in plants for
saturated fats, primarily those found in animal
products. A recent review of research done more than
40 years ago showed that this lowers blood cholesterol
levels, but is associated with increased risk for heart
attacks and premature death (BMJ, Feb 14, 2016;352:i919).
Since the majority of the scientific literature show that
polyunsaturated fats in vegetables are healthful and help
to prevent heart attacks, we have to find an explanation
of why adding large amounts of polyunsaturated fats
extracted from plants could increase the rate of heart
The old studies that substituted polyunsaturated fats
for saturated fats were done by giving vegetable oils
primarily in the form of solid margarines that were full
of trans fats, toxic aldehydes and other toxic oxidation
products. Vegetable oils extracted from their plant
sources may also be harmful because they are separated
from the protective fiber, protein, and micronutrients
that are naturally present in vegetables and seeds.
Problems of Extracted Oils
Fats are classified by their chemical structures into
saturated, polyunsaturated and monounsaturated types.
The chemical stability of a fat is determined by its
structure. All fats are made of carbon atoms held
together by electrical bonds. These bonds can be single
bonds that are stable and double bonds that are far less
stable. The stability of a fat or oil depends on the
number of double bonds between the carbon atoms. The
more double bonds, the less stable the fat.
Saturated fats have only single bonds, so they are very
stable. Polyunsaturated fats have two or more double
bonds so they are far less stable than saturated fats,
particularly when you heat them. Most polyunsaturated
oils are heated after they are extracted from vegetables
and therefore form all sorts of broken molecules. These
molecules can turn on your immunity, causing the
inflammation that punches holes in arteries to start
forming plaques that can lead to heart attacks.
Societies with the highest blood levels of
polyunsaturated fats have the highest heart attack death
rates (Ann N Y Acad Sci. Dec, 2005;1055:179-92), and
heated polyunsaturated fats are associated in humans and
animals with increased risk for cancer (BMC Medicine,
May 21, 2012;10:50; Free Radic Biol Med, Oct 15,
Which Vegetable Oils are Most Healthful?
The most healthful vegetable oils are those that are
still in plants, so they have not had to be heated and
processed, and are still paired with fiber, minerals,
vitamins and other nutrients. You get these most healthful
oils by eating nuts, avocados, beans, sunflower seeds and
other plant parts, particularly those that are high in fats.
Processing oils to remove them from their plant sources
and to stabilize them can make them less healthful. We
have already learned that the process called partial
hydrogenation, which forms trans fats, is harmful and
these oil products have largely been removed from our
food supply. However, many people are unaware that other
vegetable oils that they purchase in bottles -- corn oil,
safflower oil, peanut oil, olive oil and others -- have
been purified and stabilized through processing with heat.
Scientists have found that these heated polyunsaturated
oils are full of toxic oxidized aldehydes (Foodservice
Research International, June 2006;13(1):41 - 55).
Processed coconut oil, which is high in saturated fats,
produces the lowest levels of aldehydes, while heating
corn oil and sunflower oil produced three times more
aldehydes than were found in butter.
Low levels of aldehydes were found in olive, coconut,
avocado, peanut and rapeseed (canola) oils, butter, lard
and goose fat. High levels of aldehydes were found in
palm, corn, soy, sunflower, safflower, cottonseed, rice
bran and grapeseed oils. Using any of these oils for
frying at high temperatures considerably increases their
levels of toxic aldehydes.
• Eat lots of nuts, seeds, vegetables and fruits that are
good sources of healthful unprocessed fats --
polyunsaturated, monounsaturated and saturated.
• Restrict your consumption of bottled vegetable oils to
reasonable amounts and use them uncooked, such as for
dressing salads, or for low-temperature cooking such as
stir-frying or sauteing. Olive oil should not be used for
high temperature cooking.
• Heating polyunsaturated oils extracted from vegetables
and seeds to high temperatures can form toxic levels of
aldehydes. The higher the heating temperature, the more
toxic products are formed.
• Avoid deep-fried foods or limit them to occasional
treats. For deep-frying, I recommend using peanut oil
(high in monounsaturated fats) rather than any of the
polyunsaturated vegetable oils. In addition to the damage
to vegetable oils caused by high temperatures, foods that
are deep-fried in any type of oil or fat will contain
advanced glycation end products (AGEs) that are known
carcinogens and can increase risk for diabetes.