Trans Fat - What it is and why you DON'T want to eat it!

>> Wednesday, December 30, 2009

The last of December Rewind!  Last year we committed to drastically reducing our trans fat content.  Well, we're not ones to do things half way when it comes to our food, and I'm happy to say that trans fat has been purged from our house!  Why would we do this?  Read on and learn about this fat and why you should avoid it - and how it could be lurking in your food even if the packaging claims to be "trans fat free"!

While the main focus of this blog has been on removing HFCS from our diet, we're also taking other steps to improve the overall quality of the foods that we eat. One of the things that we're doing is phasing out bad fats and replacing them with good fats. So today, I'm going to talk about our first target - trans fat.

What is trans fat?
First, let's have a little chemistry lesson and look quickly at the three main types of fatty acids (otherwise known as fats) - saturated, monounsaturated, and polyunsaturated. (You can skip this part if chemistry is not your thing.) A saturated fat has hydrogen attached to every spot on every carbon atom in the fat and is solid at room temperature.

A monounsaturated fat contains a double bond in the carbon chain - a place where a pair of hydrogen atoms are missing. Because they are missing hydrogen atoms, it is considered unsaturated. When there are more two or more double bonds, the fat is considered polyunsaturated. Mono and polyunsaturated fats are liquid at room temperature. Olive oil is an example of a monounsaturated fat, and omega-3 oils are examples of polyunsaturated fats.

a polyunsaturated molecule

Trans fat is made when hydrogen is added to liquid vegetable oil (a nice monounsaturated fat) during a process called hydrogenation. An unsaturated fat contains double bonds. Hydrogen atoms at the double bond are usually positioned on the same side of the carbon chain (a cis molecule). During partial hydrogenation, the molecule rearranges a bit and hydrogen atoms end up on opposite sides of the double bond. This structure carries the trans nomenclature.

Unsaturated fats with the cis structure are kinked. They don't stack well and so stay fluid at room temperature. Unsaturated fats with the trans structure are straight and stack together easily. Because they stack together so easily, trans unsaturated fats solidify at room temperature. Because of their unique structure, trans fats are softer than fully saturated fats.

a monounsaturated molecule in cis and trans configurations

Double bonds in a fat are susceptible to attack by free radicals. A more saturated fat with fewer double bonds is less prone to rancidity. Hydrogenating a fat removes the troublesome attack sites and makes the fat more shelf stable. Likewise, an unsaturated fat in the trans configuration is also less prone to attack by free radicals.

Why should we care about trans fat?
In a nutshell, trans fat is an issue because it is associated with all kinds of health problems. Trans fat can wreak havoc on your cholesterol levels - increasing your LDL (the "bad" cholesterol) and decreasing your HDL (the "good" cholesterol). A high LDL is a major risk factor for heart disease. HDL picks up excess cholesterol and takes it back to the liver, so higher HDL is a good thing.

Trans fat also increases triglycerides and causes more inflammation. Triglycerides are another kind of fat that may contribute to hardening or thickening of artery walls. Trans fat consumption is associated with an increased risk of stroke and type-2 diabetes.

Where is trans fat found?
So where does trans fat hide? Not surprisingly, it's found in shortenings, some margarines, and fried foods. Because trans fat increases shelf life and flavor stability, decreases refrigeration requirements, and gives a good mouth feel, it's also rampant in baked goods - crackers, cookies, snack foods.

You can spot trans fat by looking for partially hydrogenated or hydrogenated oil in the ingredient list. All partially hydrogenated oils contain some amount of trans fat. Fully hydrogenated oils do not contain trans fat - those oils are completely saturated. Unfortunately, an oil labeled simply as "hydrogenated" may actually be partially hydrogenated and contain trans fat. Unless the ingredient list specifically states that it is fully-hydrogenated, you should assume that there is some amount of trans fat contained in the oil.

Trans fat is also naturally occurring. Small amounts of trans fat are found in dairy and meat products. Some research suggests that this naturally occurring trans fat is not as bad as man made trans fat, but results are still inconclusive.

Does zero trans fat really mean zero trans fat?
In a word, no. The FDA's rule is that a product can declare itself as trans fat free if the total fat in the food is less than 0.5 grams per serving and no claims are made about the fat or cholesterol content. There are a lot of foods out there declaring themselves trans fat free that contain partially hydrogenated oils - and the trans fat that comes with those oils.

The amount of trans fat that you consume from these products is small, but those grams of trans fat add up if a person eats more than one serving or several products containing small amounts of trans fat through the day. The FDA has not set a "daily recommended value" for trans fat consumption, but the American Heart Association does have a trans fat consumption recommendation:

The American Heart Association recommends limiting the amount of trans fats you eat to less than 1 percent of your total daily calories. That means if you need 2,000 calories a day, no more than 20 of those calories should come from trans fats. That’s less than 2 grams of trans fats a day. Given the amount of naturally occurring trans fats you probably eat every day, this leaves virtually no room at all for industrially manufactured trans fats.

How to rid your diet of trans fat
Read the ingredients! Avoid foods that contain partially hydrogenated oils or hydrogenated oils. Avoid foods with shortening or margarine, as they usually - though not always - contain trans fat. (As a side note, there are shortenings that do not contain trans fat. They accomplish that by mixing a fully hydrogenated oil, which is very hard at room temperature, with liquid vegetable oils to achieve the proper consistency.)

It's been hard, but we have managed to eliminate trans fat from our home eating. I found that task to be even harder than getting rid of all HFCS. Partially hydrogenated oils are used in so many processed foods, but most use it in small amounts and can claim to be trans fat free.  Perhaps eliminating - or at least greatly reducing - your consumption of trans fats would be a worthwhile New Years resolution?


Sagan December 30, 2009 at 9:42 AM  

Another great rewind post. I like how you've got the science of it all here too!

Amy December 30, 2009 at 3:10 PM  

That made so much more sense now that I've finished my O.Chem class!

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