Blog Directory - Blogged foodliterate: Oh My Omega

Sunday, January 27, 2008

Oh My Omega

Omega fatty acids are an interesting class of monounsaturated and polyunsaturated fats and some of them have been getting quite a lot of press. What make these fats different than the others? Well, for starters we've named them for where the double carbon-carbon bond is found in the fatty acid chain. The terminal end of the chain that contains the CH3 (methyl group) is called the omega end (the other, hydroxyl or - OH, end is the alpha end). So if the first double C=C bond is 3 carbons from the methyl group, you have an omega-3, 6 from the end gives us omega-6s and 9 from the end gives us omega-9s. Interesting, but not very special - right? Certainly not special enough for all the press, so what else is going on with these fatty acids?

The majority of the news focuses on omega-3s so let's start there. Omega-3 fatty acids are a class of fatty acids, not just a single molecule, and of these there are three nutritionally important ones. ALA (alpha-linolenic acid), EPA (eicosapentanenoic acid) and DHA (docosahexanoic acid) are all essential fatty acids, which means our body cannot produce them but must obtain them from our diet. Oils containing EPA and DHA have been shown in studies to reduce LDL (bad) cholesterol and tryglyceride levels lowering the risk of heart disease. Oily fish like salmon, cod, herring, mackerel, anchovy, and sardine are all excellent sources of EPA and DHA. ALA, found in walnuts & flax seed, has been shown to lower total cholesterol (LDL & HDL) and triglycerides in people with high cholesterol levels. And ALA can be converted in the body to EPA then DHA although not very efficiently.

Omega-6 fatty acids, like omega-3s, are not a single entity but a class of fatty acids. There are two significant omega-6s: linoleic acid (an essential fatty acid) and arachidonic acid (a pre-cursor for prostaglandins). Also like the omega-3s, these are essential fatty acids and must be consumed in our diet. Omega-6s help play a role in brain function, wound healing, and regulating metabolism. Both omega-3 and omega-6 are broken down by the same enzymes in the body so the ratio between the two is very important. It is recommended that the ratio of omega-6 to omega-3 be no more than 4:1; in fact the NIH (National Institutes of Health) recommends a 3:2 ratio with 650mg EPA & DHA, 2.2g of AHA and 4.4g of linoleic acid. This seems easy enough, but the US diet is skewed toward omega-6 at between 10:1 to 30:1. Corn oil is 46:1 (omega-6 to omega-3), soybean oil 7:1, and sunflower oil is all omega-6 with no omega-3.

Why is this so important - these are essential fatty acids, why do we need to worry about ratio & quantity? To paraphrase Paracelsus "the dose makes the poison". Omega-6s produce inflammatory metabolites in the body. And omega-3s while better are not without their own risks at high levels. According to the Center for Food Safety & Nurtrition (CFSAN) the known or suspected risks associated with EPA & DHA (at levels greater than 3 grams per day) include: increased bleeding - especially in those taking aspirin and coumadin, reduced glycemic control among diabetics, the possibility of hemorrhagic stroke in very large amounts, supresssion of immune and inflammation responses and decreased resistance to infections. In fact, they recommend that anyone with congestive heart failure, chronic recurring angina or insufficient blood flow talk with their doctor before taking omega supplements or eat foods containing large quantities.

There is also a group of omega-9 fatty acids, which I'm going to guess you have never heard about. You may however, have heard of oleic acid which is an omega-9 and is a major component of olive oil and other monounsaturated fats. The reason this category doesn't get the same level of press is because these are not essential fatty acids, our bodies can manufacture these from the other fats that we consume and because omega-9s are common components of both animal fats and vegetable oils.

Since most of the fats I've been writing about have one or more double carbon-carbon bonds, I would be remiss not to talk a little about trans fats as well. Any fat with a C=C bond has a configuration, meaning the hydrogen atoms are either attached to the same side or to opposite sides of the double bond. When the hydrogen atoms are on the same side of the double bond, it is called a cis isomer. When the hydrogen atoms are on opposite sides of the double bond, it is called a trans isomer. Most, but not all naturally occuring fatty acids are cis isomers and their chains usually have a "V" shape. Because the hydrogens are on opposite sides of the trans isomers, their chains are usually straight like saturated fats. About 25% of our diet comes from naturally occuring trans fats, found in animal and dairy fats, while the other 75% comes from hydrogenated mono & poly fats. It is that 75% that has been in the news as of late as all of the food manufacturers scramble to find a suitable replacement for these trans fats.

Trans fats are used (were used?) in processed foods because of their stability and low oxidative reactivity. Cis configurations, because of the "V" shape, can't really align or stack up on one another and so are liquid (or soft) fats, and are easily degraded by oxygen and free radicals reducing the fat's shelf-life and causing the fat to become rancid (smells like paint). Trans configurations look & behave more like a saturated fat, and it is this characteristic that made it such a useful ingredient and is why it is not easily replaced - no one wants to replace it with sat fat since that really isn't a healthier option, both are known to increase cholesterol levels. Our diets have consisted of about 14% saturated fat & 3% trans fat since the 1960's but until recently the research wasn't in to show how trans-fats caused many of the same health related problems as sat fats. It is highly recommended that we reduce the quantities of both (sat & trans) in our diets, but not eliminate them completely.

Well, you are now up on all the latest buzz about fats and will be able to better understand fact from hype. You also now possess a foundation about food components (protein, carbohydrates & fat) upon which new information can be built. I'm not sure yet what the next topic will be, so if there is something you've been wondering about or simply have a suggestion for a topic, please drop me a line - I'd love to hear what's on your mind!


Anonymous said...

Hi, very interesting post, greetings from Greece!

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