OVERVIEW

Dietary fats are often maligned as making a person "look fat." This is only partly true. The whole truth is that eating more of ANY of the three macronutrients - carbohydrates, protein, or fats - than you body needs will result in the excess being converted to fats and stored in un-flattering places.

Fats are an important part of a healthy diet. Some fats (the so-called omega-3 and omega-6 fatty acids) are actually essential for human health. Our bodies cannot make these fats, but we must have them in order to make a number of different hormones as well as for healthy cell membranes and our brain. Our bodies can naturally make other kinds of fats whenever they are needed or whenever we eat more macronutrients than our body currently needs.

There are a number of ways to classify different kinds of fats, which will be discussed below. In some cases, these classifications overlap and for this reason, the literature discussing fats is sometimes ambiguous. Please click on the highlighted links for further discussion of each of these different types of fat!

Basic Chemical Structure of Fats

First we have to describe the basic chemical structure of fats, since all the different classifications of fat revolve around subtle changes in their chemical structure.

All fatty acids consist of two parts:

  1. Carboxylic Acid Head: This has the chemical formula COOH, and has two important properties: it can react with other things, like alcohols, amines, etc, and it likes to mix with water.
  2. Hydrocarbon Chain Tail: This is just a string of carbons tied together, with hydrogen hanging off the sides. Depending on the number of carbons in the chain, the properties are different. We can talk about "short chains", "medium chains", and "long chains" Short chains are similar to butane (lighter fluid), medium chains are similar to gasoline, and long chains are similar to Vasaline (petroleum jelly). The hydrocarbon chain tail does not like to mix with water.

All fatty acids have the same COOH "head"; the variation in the "tail" is where all the interesting things happen. For example:

  • If the hydrocarbon chain length is only one carbon long, then we have acetic acid, which when diluted in water is what we call "vinegar". It also gives rise to the very important acetyl group that is important to many biochemical processes in the body. [We don't usually think of vinegar as a fat, but it has the structure of a fat].
  • Fatty acids with a hydrocarbon chain length of 8 to 12 carbons are called medium chain; short chain have fewer than 8 carbons, and long chain have more than 12 carbons. Oils formed from medium chain fatty acids are sometimes abbreviated MCT.
  • If every carbon of the tail has 2 or 3 hydrogens attached, then we say that the fat is saturated. Animal fat (and fat made by people) is naturally saturated. This is sometimes abbreviated SFA.
  • If one hydrogen is removed on each of two adjacent carbon atoms in the chain, then we say the fatty acid is unsaturated and has a double bond between the two involved carbons.
  • When a double bond is formed (as above), there are two different geometric shapes that can result, which we call cis and trans. The cis form is natural, whereas the trans form only occurs during chemical processing.
  • When a fatty acid contains only one double bond, we say that it is mono-unsaturated. This is sometimes abbreviated MUFA.
  • When a fatty acid contains more than one double bond, we say that it is poly-unsaturated. This is sometimes abbreviated PUFA.
  • Poly-unsaturated fatty acids are further characterized by specifying how close to the tail-end the first double bond occurs. This location is given an "omega" number, such as omega-3 or omega-6. [Omega is the last letter of the Greek alphabet; alpha is the first].
  • The length of the hydrocarbon tail determines the overall solubility of the fatty acid in water versus oil, and the transport mechanism within the body.

Often, three fatty acid molecules are found combined with one glycerine molecule, which is then called a triglyceride. This is the normal form in which most fatty acids are found in our food.

Fats can be either liquid or solid, depending on the temperature. As a general rule:

  • Fats with higher carbon count solidify at lower temperature.
  • Saturated fats solidify at a lower temperature than unsaturated fats with the same carbon count.
  • Trans-fats solidify at lower temperature than cis-fats with the same carbon count.

In general, the more double bonds are in a particular fat, the faster it will "spoil", become "rancid", or (technically) "oxidize."

Minimally processed vegetable oils (e.g. olive oil) contain other constituents such as polyphenols, tocopherols, and other antioxidants. These oils are labeled as "virgin"; other vegetable oils (e.g. corn oil) are more highly processed and have less of these beneficial constituents.

It must be emphasized that commercially available fats and oils are mixtures that include various proportions of saturated, mono-unsaturated, omega-3, and omega-6 oils. Each must be judged by the relative percentage of each of these components. See for example [Healthline].

Fats and Cell Membranes

All cells are enclosed by a "membrane" that separates the inside of a cell from the outside. These cell membranes are basically formed from fats as a "bilayer" in which the inside and outside of the membrane exposes the fatty acid "heads" (or chemical derivatives of such as phosphates called phospholipids) that interact well with aqueous (water) content inside and outside the cell.

The fatty acid "tails" are found in between the inside and outside of the cell membrane. These tails do not like water, but do like to associate with each other.

These membranes contain a mixture of satutated and unsaturated fats, as well as steroids including cholesterol, and various protein structures.

Dosage:

REFERENCES