Hi,
Below's some information on canola oil and other vegetable oils.
Jeanne
Ask the Expert: Concerns about canola oil | The Nutrition Source |
Harvard T.H. Chan
https://www.hsph.harvard.edu/nutritionsource/2015/04/13/ask-the-expert-concerns-about-canola-oil/
School of Public Health
The expert: Dr. Guy Crosby
I’m confused about whether canola oil is healthy. I know that it’s a
polyunsaturated fat, which I’m told is good, but then I also hear that
I should stay away from it.
Some of the claims:
• Most canola is chemically extracted using a solvent called hexane,
and heat is often applied which can affect the stability of the oil’s
molecules, turn it rancid, destroy the omega-3s in it, and can even
create trans fats.
• “Cold-pressed” canola oil exists but is very expensive and hard to find.
Should I avoid canola oil?
And what are the best fats in general for cooking?
The top four vegetable oils consumed in the United States are soybean,
canola, palm, and corn oil. These are referred to as refined,
bleached, deodorized oils – or RBD for short – because this describes
the process by which they are manufactured.
• RBD oils are produced by crushing the plant material, usually seeds,
to express the oil, followed by extraction of the crushed material
with a low-boiling solvent, most commonly hexane, to obtain the
remainder of the oil.
• Canola oil is generally considered a “healthy” oil because it is
very low in saturated fat (7%). Like olive oil it is high in
monounsaturated fat (63%).
• Canola oil also contains a significant level of polyunsaturated
omega-3 (ω-3) fat (9-11%),
• In addition, canola oil contains significant amounts of phytosterols
(about 0.9% by weight) that reduce the absorption of cholesterol into
the body.
As with many highly processed food products there are concerns about
the safety of canola oil.
First is the use of a solvent such as hexane to extract the maximum
amount of oil from the seed. Hexane is a very volatile solvent
(boiling point 69ºC, or 156ºF) with a very low toxicity (LD50 in rats
of 49.0 milliliters per kilogram). Hexane has been used to extract
oils from plant material since the 1930s, and “there is no evidence to
substantiate any risk or danger to consumer health when foods
containing trace residual concentrations of hexane are ingested.”
It has been estimated that refined vegetable oils extracted with
hexane contain approximately 0.8 milligrams of residual hexane per
kilogram of oil (0.8 ppm). It is also estimated that the level of
ingestion of hexane from all food sources is less than 2% of the daily
intake from all other sources, primarily gasoline fumes. There appears
to be very little reason for concern about the trace levels of hexane
in canola oil.
Another concern is the report that canola oil might contain trans-fats
that have been linked with significant health problems. In fact,
canola oil does contain very low levels of trans-fat, as do all oils
that have been deodorized. Deodorization is the final step in refining
ALL vegetable oils. This process produces the bland taste that
consumers want.
As a comparison, the fat of cattle and sheep, as well as the milk
obtained from cows, contain about 2-5% of natural trans-fat as a
percent of the total fat. [3] When canola oil is deodorized it is
subjected to temperatures above 200ºC (as high as 235ºC, 455°F) under
vacuum for various lengths time to remove volatile components such as
free fatty acids and phospholipids. During exposure to these high
temperatures a small amount of the unsaturated fatty acids, especially
the essential ω-6-linoleic and ω-3–linolenic acid, are transformed
into trans-fatty acid isomers. Because of earlier studies showing that
even quite low levels of trans isomers of ω-3–linolenic can have
adverse effects of blood cholesterol fractions, the processes used for
deodorization have been modified to limit the production of these
compounds.
Other vegetable oils, and even nut oils, have been found to contain
levels of trans-fatty acids that are comparable to the levels in beef
fat. The table below summarizes the content of trans-fatty acids found
in a number of oils. In both canola oil and soybean oil,
trans-isomers of linoleic acid have been found to account for 0.2-1.0%
of total fatty acids, while trans-isomers of linolenic acid may total
as much as 3%. Linolenic acid isomerizes with heat about 12-15 times
faster than linoleic acid.
Oil Trans Content (%)
Soybean* 0.4-2.1%
Walnut* 2.0-3.9%
Sunflower 1.1%
Canola* 1.9-3.6%
Olive 0.5%
PH soybean oil** 43.6-50.2%
*Results of multiple samples of commercial oil
** Partially hydrogenated soybean oils for comparison
A consequence of transforming some of the natural unsaturated fatty
acids to trans-fat during the deodorization step is a reduction in the
content of beneficial ω-3–fatty acids.
• Heating bleached canola oil at 220°C for ten hours reduces the
content of linolenic acid by almost 20%. Keep in mind that canola oil
sold in the supermarket still contains 9-11% natural ω-3–linolenic
acid.
• The same transformation occurs during commercial deep-fat frying
operations with canola oil. Thus canola oil used to fry French fries
for seven hours per day for seven days at 185°C (365°F) resulted in
increasing the total trans-fatty acid content of the oil from 2.4% to
3.3% by weight of total fat.
• Of potentially greater concern is the formation of oxidation
products of polyunsaturated fatty acids during prolonged commercial
deep-fat frying. But this is less of a concern for canola oil than for
oils with higher levels of more readily oxidized polyunsaturated fat
such corn, soybean, sunflower, and safflower oils.
When considered in the context of other commercial fats, the low
trans-fat content of canola oil is no different from other vegetable
oils. But one word of caution is appropriate. Bottles of canola,
soybean, and corn oil in the supermarket proudly proclaim “Contains
zero grams of trans-fat.” Read the fine print that states zero grams
of trans-fat per serving, which is only one tablespoon, or about 14
grams of oil. The FDA allows any component that is less than 0.5 grams
per serving to be listed as zero grams! Despite this claim, virtually
all vegetable oils sold in the supermarket contain small amounts (less
than 5%) of trans-fat.
So what other options are there if one wants to avoid RBD oils?
Should a consumer want to avoid RBD oils, cold-pressed oils can be an
option, since they are not treated with heat, not extracted with
solvents, and not deodorized. Depending on the type, these oils may
feature a range of descriptions on their labels, such as
“cold-pressed,” “unrefined,” “virgin,” etc. Due in part to their
higher price point, adulteration of these types of oils (such as
undisclosed “blending” with an RBD oil) has been an issue, so
consumers looking to completely avoid RBD oils may also want to select
high-quality oils from reputable sources, or those that have been
verified to meet quality standards.*
Given the above information, is commercially processed canola oil harmful?
Although care must be taken in handling and processing of canola oil
and other vegetable oils, canola oil is a safe and healthy form of fat
that will reduce blood LDL cholesterol levels and heart disease risk
compared to carbohydrates or saturated fats such as found in beef
tallow or butter. Indeed, in a randomized trial that showed one of
the most striking reductions in risk of heart disease, canola oil was
used as the primary form of fat. Whether using cold-pressed canola
oil provides some small additional benefit is not clear.
In general, variety is a good strategy in nutrition, and thus
consuming a variety of oils is desirable, for example using extra
virgin oil when the special flavor is desired and canola oil or
soybean oil for other uses. Both canola and soybean oils provide ω-3
fatty acids that are important to include in an overall diet. Of
course, avoiding overheating and burning of oils is important to
provide the best taste and to avoid damaging the healthy-promoting
fatty acids that they contain.
_______________________________________________
Cookinginthedark mailing list
Cookinginthedark@acbradio.org
http://acbradio.org/mailman/listinfo/cookinginthedark
