Blog Directory - Blogged foodliterate: January 2008

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!

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!

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!

Saturday, January 5, 2008

Change is Good

Happy New Year! I'm back from the holidays and ready to continue our discussion on starches. Last post I talked about unmodified starch and its properties. Today, I'm going to talk about modified starches as you are far more likely to see these in the foods you buy and now you can understand more about why they were chosen.

Unmodified starches, like the corn starch that is in your pantry, thickens really well but has some major limitations. When heat is applied to starch and water the starch swells - also known as gelatinization. The starch granules separate as they absorb water and the slurry becomes viscous (thick). When this gel cools the starch molecules start to realign causing 'set-back' or an additional thickening - think cold gravy. Unfortunately as the realignment occurs, the starch molecules form hydrogen bonds and those squeeze out water - this is called syneresis. And as if this particular issue wasn't enough, unmodified starches can't be frozen. Well you can freeze them, but what they turn into once thawed isn't pretty. Plus as you have probably noticed, unmodified starch won't thicken in cold water and they clump terribly in hot water. Essentially there are a lot of problems that need to be overcome for use in processed foods.

So, what are we to do? Modify the starch to suit our needs of course. There are a number of chemical and physical modifications that are done to native (unmodified) starches to imbue them with the desired characteristics. Modified starches were developed in the 1940's and over the years the range of modifications has increased. Some of the modifications have led to the development of freeze-thaw stable starches, retort stable starches (like in canned soups), fat replacement (low-fat salad dressings), emulsification, pulpy starches, and instant starches.

One of the most common chemical modifications is cross-linking. It is achieved by reacting compounds, usually esters, with the hydroxyl groups on the starch molecules, i.e. cross-linking the starch molecules to each other. This modification provides resistance to temperature, acid and shear. Another common modification is substitution as it is used to provide freeze-thaw stability. This process involves scattering anionic groups, like acetates and phosphates, at the starch molecules to prevent the realignment of the starch molecules so retrogradation/syneresis can't occur.

Physical modifications can be used to produce a cold-water swelling or instant starch. The starch is slurried (mixed with water), then heated with steam to hydrate/gelatinize the molecules and then dried. These starch molecules are now porous and quickly resolubilize when reintroduced to liquid. Our instant puddings just wouldn't be the same without them!

Fibers are also used in processed foods, to provide not just nutrition, but also texture, moisture retention, and mouthfeel. One of the newest forms of functional fiber is resistant starch; while not technically a fiber, it is a starch, the body processes it physiologically like a fiber. It reaches the intestines where is is fermented by the intestinal flora just like a fiber. Resistant starch are primarily used in baked goods and cereal products, but new applications are being developed.
Well, we have spent a good bit of time on carbohydrates, but with the new year, its time for a new topic. Let's move on to fats - and not the kind we are all trying to work off from eating too many holiday treats!