Its true... Hydrogenated oils arent as bad as partially hydrogenated oils.
Here is a post I made a while back on it. I was responding to someones question about canola oil bit it does explain it a bit and is good to know.
There was a post here earlier that I am replying to but for the life of me cant seem to find it.
Anyway the poster asked if canola oil was hydrogenated and I began to respond explaining that it wasn't hydrogenated but oxidized (rancid) and wanted to add this about hydrogenation.
Since I cant find the original post I will just stick it here and hopefully the person who asked will read this too. Sorry.
I will also add that Hydrogenation and Oxidation of oils are 2 different things.
Polyunsaturated oils don't hydrogenate or create trans fatty acids by being exposed to high heats alone.
What I am posting is a mishmash of clips from a few different sources that I lumped together to try and make this as clear and brief as possible. I will post the links to where I got this from at the bottom of this. I hope its clear enough and makes sense the way I mushed it together. Also the graphics I used were from different sources but thought they would be helpful.
The idea that cooking with heat damages the oils that are highly polyunsaturated is true and the warning against cooking or frying using fragile oils such as flaxseed oil is valid, but not because trans fats are formed. What is formed under harsh circumstances such as high-temperature cooking and frying is a polymerized oil, and this is because the heat has helped to form free radicals and then various breakdown products. (Flaxseed oil that is still in the ground seed can be heated in baking and it does not become damaged.)
One reason the polyunsaturates cause so many health problems is that they tend to become oxidized or rancid when subjected to heat, oxygen and moisture as in cooking and processing. Rancid oils are characterized by free radicals—that is, single atoms or clusters with an unpaired electron in an outer orbit. These compounds are extremely reactive chemically. They have been characterized as "marauders" in the body for they attack cell membranes and red blood cells and cause damage in DNA/RNA strands, thus triggering mutations in tissue, blood vessels and skin. Free radical damage to the skin causes wrinkles and premature aging; free radical damage to the tissues and organs sets the stage for tumors; free radical damage in the blood vessels initiates the buildup of plaque. Is it any wonder that tests and studies have repeatedly shown a high correlation between cancer and heart disease with the consumption of polyunsaturates?32 (Pinckney, Edward R, MD, and Cathey Pinckney, The Cholesterol Controversy, 1973, Sherbourne Press, Los Angeles, 130; Enig, Mary G, Ph D, et al, Fed Proc, July 1978, 37:9:2215-2220) New evidence links exposure to free radicals with premature aging, with autoimmune diseases such as arthritis and with Parkinson's disease, Lou Gehrig’s disease, Alzheimer's and cataracts.33 (Machlin, I J, and A Bendich, FASEB Journal, 1987, 1:441-445 )
Hydrogenation is a commercial chemical process of forcing hydrogen atoms into the holes of unsaturated fatty acids. This is done with hydrogen gas under pressure with a metal catalyst at a temperature of 248-410 degrees F (120-210 C).
This is considered 100% hydrogenation and will chemically saturate the fatty acid with hydrogen. In other words liquid oil will turn into a solid fat.
100% Hydrogenation: The above illustration shows how Alpha-Linolenic Acid looks completely hydrogenated. The red H's show where the holes in the molecule were before the hydrogenation process was started. Notice all the holes are filled. This now has the same configuration as Stearic Acid! (But there is a slight difference: This converted fatty acid now has trace elements in it from the hydrogenation process catalyst.) Also animal fats seldom have more than 70% saturated fatty acid radicals, lard for example has 54% unsaturated fatty acid radicals. It has also straightened out
and its melting point has changed from 10 degrees F (-12 C) to that of Stearic Acid, 158 degrees F (158 C).
If the manufacturers produced margarine and shortening in this way there would be fewer problems. You see, saturated fatty acids have no room in them for shifted bonds or hydrogen atoms in the trans- configuration. That requires holes. But unfortunately, Stearic Acid is just too hard a fat to be made into margarine or shortening. Trans fatty acids are present mainly in partially hydrogenated fats, but they are also present in hydrogenated fats because chemical reactions never achieve 100% efficiency.
Partially hydrogenated fats
Not too hard - not too soft... Of course, vegetable oil is too soft for margarine or shortening because it is liquid. Saturated fat is too hard. Margarine requires something in the middle. And here is where the problem lies. Margarine and shortening makers `partially hydrogenate' their product. They only add hydrogen atoms until the oil is at the desired consistency. For our health this does terrible things. These oils are also produced at high temperatures with metal catalysts and pressurized hydrogen, but the process is stopped when the oil has the proper consistency for its application. The high temperatures and catalysts used for this chemical reaction weaken the double bonds and, as a side effect, cause a large percentage of the natural Cis double bonds to change to Trans double bonds.
During the hydrogenation process, hydrogen atoms are inserted in no particular order. (Nature does it in a very controlled way.) When they stop the incomplete hydrogenation process, unsaturated fatty acids are in varying stages of hydrogenation. Some molecules are mostly hydrogenated, while others are not. And the double bonds have often shifted to unnatural positions. Each molecule can be in varying cis-/trans- configurations.
Mr. Erasmus has stated, "So many different compounds can be made during partial hydrogenation that they stagger the imagination. Scientists have barely scratched the surface of studying changes induced in fats and oils by partial hydrogenation."1 (References: 1. Fats that Heal and Fats that Kill pg. 103)
The end result is many of these altered substances are toxic to our systems. One study has shown up to 60% trans- fatty acid content was found in some margarine, with less than 5% essential fatty acids remaining. The average trans- fatty acid content of stick margarine made in this way is 31% with a range of 9.9 to 47.8%.
Links (where I swiped this stuff from)