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 
attacks.

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, 
2007;43(8):1109-20).

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.

My Recommendations
• 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.