Apologies if everyone already knows this, but I have a point to make that needs a very long intro to have a chance of ensuring that the point gets across.

Oils are made of atoms of carbon, hydrogen, and oxygen. The atoms are arranged in a specific way, following specific rules. You can think of atoms like little Legos, but they don't quite connect the same. Hydrogen has a single connector and can connect to a single other atom. Oxygen has two connectors and can connect them to one or two other atoms. Carbon has four and so can connect to up to four other atoms (but could connect to as few as two). (For anyone keeping track, nitrogen generally has three.)

So when we're talking about, say, carbon dioxide, we're talking about two oxygen atoms attached to a carbon atom, and one way to depict this is as so:

O=C=0

The O is oxygen, the equal signs represent "double bonds" (two from each oxygen each connected to two of the "connectors" on the carbon).

Water could be represented as:

H-O-H

The H is hydrogen, the O is oxygen, and the hyphens represent "single bonds" (one from each hydrogen connected to one of the available "connectors" on the oxygen).

This doesn't accurately depict the shapes properly -- I'm limited with what I can do in HTML text. The "connectors" on the oxygen, for example, actually are closer together on one side. I'll have more comments on this later.

Here is an example of an omega-3 fatty acid:

    H H H H H H H H H H H H H H H H H
    | | | | | | | | | | | | | | | | |
O=C-C-C-C-C-C-C-C-C=C-C-C=C-C-C=C-C-C-H
  | | | | | | | |     |     |     | |
  O H H H H H H H     H     H     H H
  |
  H

Some comments on this. This is a long chain of eighteen carbon atoms, with a lot of hydrogen, and a little bit of oxygen at the end. It's that configuration of oxygen plus that little dangling hydrogen atom that makes this an acid. That's the only hydrogen atom in this system that can become "acidic" (unless the molecule is altered in some way).

The chain of carbon atoms looks like it's straight, but it's really more zig-zaggy on the left half. On the right half, every where there's one of the double bonds, the chain actually bends pretty significantly, making this molecule anything but a nice straight line.

This fatty acid is considered "unsaturated". Unsaturated means that there are places where hydrogen atoms could go on this chain, by getting rid of those double bonds between carbon atoms and instead attaching hydrogen to the carbon atoms (instead of the carbon atoms to each other). If there are no double bonds at all, it is called "saturated". If it has many double bonds, like the example above, it's called "polyunsaturated". If it only has one double bond, it's called "monounsaturated". An example of the above in a saturated configuration would be:

    H H H H H H H H H H H H H H H H H
    | | | | | | | | | | | | | | | | |
O=C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
  | | | | | | | | | | | | | | | | | |
  O H H H H H H H H H H H H H H H H H
  |
  H

The molecule is a lot more boring this way, and while the carbon atoms zig-zag back and forth (kinda like a \/\/\/\/\/\ arrangement), the molecule isn't really "bent" any more. It's also no longer an "omega-3" fatty acid, because "omega-3" means that the first double bond occurs at the third carbon atom from the right end (the end without the oxygen). An omega-6 fatty acid has its first double bond between the sixth and seventh carbon atoms from the end. An omega-9 fatty acid has its first double bond between the ninth and tenth carbon atoms from the end.

Hydrogenation is a process that tries to convert bent molecules to straighter ones by adding heat (say, 500 degrees) plus hydrogen gas (H2). The reason for this is because, the more bent the molecules are, the harder it is for them to line up nicely and be solid. Instead, they don't line up and remain more liquid at room temperature. The more saturated the molecules, the more easily the molecules can line up together, and so the easier it is for them to become solid.

There are a couple of ways that hydrogenation straightens molecules.

The first way it can happen is by adding two hydrogen atoms to a molecule where a double bond sits. By getting rid of the double bond between carbon atoms, the molecule straightens out. Biologically speaking, this isn't such a big deal. While doing this to an omega-3 fatty acid makes it less suitable for use as part of cell structure, for example, the body can still break down this kind of fat for energy.

The second way is to bend the molecule back into a straight form without getting rid of the double bond. As an example of this, consider:

    H H H H H H H H H H   H H H H H H
    | | | | | | | | | |   | | | | | |
O=C-C-C-C-C-C-C-C-C=C-C-C=C-C-C=C-C-C-H
  | | | | | | | |     | |   |     | |
  O H H H H H H H     H H   H     H H
  |
  H                     ^-- that one flipped sides

Notice how the second double bond has changed. Instead of having both hydrogens on the same side, one of the hydrogen atoms has switched sides. This has the effect of straightening out the molecule (there's a bit of a zig at that point, but it's a lot straighter). This is now an example of a trans-fat.

In the trans configuration, the hydrogens are on opposite sides of the double bond. In contrast, when the hydrogens are on the same side, it's called "cis". (Cis means "on the same side of". "Cisatlantic" is the opposite of "transatlantic".)

The trans configuration does not occur in nature (or is exceptionally rare). The problem here is that, because it has changed the shape in a particularly unnatural way, it is between difficult and impossible for the body to handle these properly.

You may have some idea that chemicals called enzymes are involved in breaking down fats and sugars and proteins (and lots of other life functions in all living cells). The way enzymes typically work is based on the shape of the molecule being a perfect match for wedging itself into and between two parts of a molecule, or for fitting two molecules together to get them to react together. To make an exceptionally long story (that I probably couldn't tell you, anyway) short, when fat molecules are in the trans configuration, the enzymes that would break them down don't fit right.

So the body has to get creative about dealing with them, and exacty how the body handles these trans fats is still being studied. I've heard (warning: hearsay) that researchers are finding that trans fats are being used in cell membranes in human cells, but what effect this substitution is having on cells is not yet understood.

To be continued...