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Saturday, January 12, 2008

Fat Facts

Ahh, fat, the last of the trio of compounds so essential to our nutrition. Unfortunately, it has a really bad reputation that it doesn't fully deserve. It is more correct to use the term lipid since this is the category of chemical compounds that fat belongs to. Lipids consist numerous fatlike compounds that are insoluble in water and include mono-, di-, and triglycerides, sterols, phospholipids, fatty alcohols, and fatty acids.

Chemically fats are different from carbohydrates and proteins in that they are not polymers of repeating molecules, don't form really long molecular chains, and contain 2.25 times the calories (9 kcal/g vs. 4 kcal/g).

CHEMISTRY ALERT! A typical fat molecule has a glycerol backbone with fatty acids attached.

butyric acid (fatty acid)

The hydroxyl (OH) groups on both the glycerol and fatty acid are reactive and when they hook-up a water (H2O) molecule is kicked out. If three fatty acids are attached to the glycerol, the molecule formed is a triglyceride. There are about 20 different fatty acids that are most commonly attached to the glycerol that all differ in length and in their number of hydrogen (H) atoms. The shortest fatty acid is formic acid with a single carbon atom and one of the longest has 28 carbon atoms.

As much maligned at fat is, we still need it in our diet. Dietary fats supply energy, carry fat soluble vitamins (A,D,E,K) and hormones and are a source of antioxidants. Fat is also incorporated as a structural component of our brains, nerve cells and cell membranes. It insulates us against the cold and pads our internal organs.

As for fat in food - it has some interesting properties as well. They don't have a sharp melting point but, as you've no doubt noticed, gradually soften upon heating. And unlike water, fat can be heated well above 212F and can therefore brown foods. However, if you keep heating it it will smoke, flash and eventually ignite; this is important since not all fats are created equal and these events will happen at different temperatures with different fats. Fat is a lubricant in food and interacts with protein and starch to make foods tender (like marbling in steaks and shortening in pie crusts). Fat also contributes flavor, both on its own and by carrying fat-soluble flavors. And perhaps most importantly, small amounts of fat contribute to the feeling of satiety; it helps signal the brain that we are full.

Well, there is quite a bit more to learn about fat so next post I'll talk you about mono-, poly-, and saturated fats as well as the very topical omega-3s and trans fats. Take care!

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