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Monday, January 21, 2008

Chewing the Fat

Welcome back! Last post I introduced you to lipids, more commonly referred to as fats. Today I'll continue this topic and get into some more detail (read Chemistry!). I'm sure everyone has seen or heard about saturated, monounsaturated and polyunsaturated fats; you can often find one or more of them on the nutrition facts panel of the foods you buy. But I'm guessing not all of you understand what these are and how they differ from one another, so lets start with the dreaded saturated fat.

Last week I wrote about fatty acids, and how they are chains of carbon atoms with a hydroxyl group (-OH) at one end. If you remember high school chemistry you may recall that carbon atoms want to have 4 other atoms attached. Saturated fatty acids are exactly that, each carbon atom has the maximum number of atoms attached to the chain, so there are no double carbon bonds and the molecule is said to be "saturated".

This is butyric acid, found in butter, and it is a saturated fatty acid. Saturated fats are primarily found in animal and dairy products, and are generally solid and opaque at room temperature. Of course there are exceptions to this - 2 plant oils also contain high amounts of sat fat: coconut and palm, and they are semi-solid at room temperatures. Saturated fats are the ones the nutritionists are always telling us to avoid because they raise cholesterol levels and impact the development of ateriosclerosis. More specifically, three types of saturated fats raise cholesterol levels: Lauric acid, Myristic acid, and Palmitic acid. Unfortunately, these 3 fatty acids comprise 2/3 of the saturated fats in the US diet.

This is Oleic acid - one of the monounsaturated fatty acids and the most prevalent fatty acid found in nature. Monounsaturated fats, as you can see, have one unsaturated carbon bond, thus resulting in a double carbon bond. Monounsaturated fats are found primarily in vegetable oils like olive (really high in oleic), canola, peanut, and in foods like avocados, nuts and fish. Monounsaturated fats are generally cholesterol neutral, they neither raise nor lower your levels. But like sat fats, there is an exception to this too - the category of mono fats known as omega-9, to which oleic acid belongs, have been found to lower cholesterol levels (I'll talk about omega fatty acids in my next post!). There are also some specific benefits associated with mono fats; those who have insulin-resistant or non-insulin dependent diabetes can mitigate hypertriglycemia and hyperglycemia by increasing their intake of mono fats at the expense of carbohydrates.

That leaves us with polyunsaturated fats, which have two or more double carbon bonds like this : This is linoleic acid, one of the most common polyunsaturated fatty acids (both in nature & in our diet), one of the omega-6 fatty acids, and one of the essential fatty acids. Polyunsaturated fat is found in safflower, corn, cottonseed, and soy oils as well as fish and nuts. This category of fatty acids has been found to reduce cholesterol; and it is recommended that you consume 2:1 poly fats to sat fats. So, why don't we just eat more poly fats? Well it has to do with that golden rule - everything in moderation. Epidemiologic data suggests that high linoleic acid consumption can increase the risk for cancer because it enriches the cell membrane phospholipids and predisposes them to free-radical oxidation.

So, you now can be a better informed label reader when you are scanning those nutrition facts panels and see the fat breakdown. I also hope that you understand a bit more about the fats that make up our diet. Next time I'll fatten you up on facts about trans-fats and omega fatty acids!

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