Does "partially hydrogenated" mean trans fat?

My understanding is that partially hygrogenated would be trans fats. So, what you're saying is quite interesting. I know that if the label says "total fats" and the amounts listed on the specific types, then there is additional unlisted fat which is most likely hydrogenated. But to say there are no trans fats and list the ingredients with what is a trans fat would be worth calling and checking up with the company. And then let us know.

to clarify about the total fats sentence above, if the listed types of fats add up to less than the total fats, then it is likely that the difference are bad kinds of fats that they don't want to name.

Here is an example of what I'm talking about: In a bag of Nacho Cheese doritos, the bag says "Trans Fat O grams." But then looking at the ingredients it says "partially hydrogenated soybean and cornseed oil." Is this a discrepency? Ingredients listed here: http://www.fritolay.com/fl/flstore/cgi-bin/products_doritos.htm

Patirally hydrignated oils are very bad. They can be free of trans-fat, depending on what oil they partially-hydrignated. The bad thing is that p-h oils are very high in carcinogens, which are cancer causing agents.

I thought that trans fats are "totally hydrogenated;" while partially hydrogenated are just that: partially. Still the same thing, but one is it totally and one only partially.

Answer in two parts:Far as I know, the "trans" in trans-fat is an adjective referring to the opposite of "cis", and these terms are used to describe the shape of molecules. A fatty acid is a long chain of carbon atoms connected to each other with hydrogen atoms stuck on the sides. Imagine a centipede. The body sections are the carbons and the legs are the hydrogens. The difference is that fatty acids can be missing some hydrongens: they're centipedes missing some legs. Saturated fats have all the hydrogens (or centipede legs) they can. Mono-unsaturated fats are missing one hydrogen/leg, and poly-unsaturated fats are missing multiple hydrogens/legs. Cis and trans refer to which side of the centipede body is missing legs. Cis basically means "on the same side", while trans more or less means "on opposite sides". Cis unsaturated fats have hydrogens/legs missing on both sides of the body. This uneven distribution makes the molecule kink up. Trans unsaturated fats are missing legs only on one side. That makes them stay straighter, all the better to clog your arteries.

part two: hydrogenation

Whoops! Sorry about that. Cis fats have legs missing on the same side and trans fats have legs missing on different sides. Hydrogenation means adding back hydrogen legs to the fatty acid cetipede. If you fully hydrogenated you'd add back all the possible legs. Partial hydrogenation adds back only some legs. So? Well, if you add legs and fill in only one side of the centipede then you get a cis fatty acid. Then you'd have partially-hydrogenated fat but no trans fat. If you add the hydrogens to both sides then you get partially hydrogenated fat that's also trans fat because there are legs missing on both sides. Again, sorry about that typo.

also wondering if something is just labled "corn oil" could that be trans fat or would it have to be hydrogenated?

Yes, they have trans fat! The FDA gave in to the food industry and let them label foods with "O grams" if it has actually 2 grams or less a serving!!! Don't eat anything that has partially/hydrogenated oils!