Say No to Trans-fat

Trans-fat impairs cholesterol metabolism and is linked to heart disease.  Formed by turning a smooth vegetable oil into a solid fat, the rigidity of a trans-fat is what makes pie crusts flake or cakes crumble.  The rigid nature also helps products stay on the shelf for a longer period of time.  Besides cakes and pies, common sources also include cookies, peanut butter (think Jif and Skippy), crackers, potato chips, margarines and shortenings, fried fast food, French fries, some frozen pre-made foods, and donuts.  It is easy to detect when a product has trans-fat.  Look at the product’s list of ingredients for a “partially hydrogenated oil” or “vegetable shortening.”   Beware, even if the nutrition facts panel states zero grams, a product is still allowed to contain trans-fat if there is 0.5 grams of less per serving.  Alas, no one eats one serving of chips, Skippy peanut butter or French fries, so the person is bound to consume more than 0.5 grams of trans-fat when eating these foods.  The Institute of Medicine’s (IOM) goal for trans-fat intake is to consume zero grams per day, or as low as possible while consuming a nutritionally adequate diet.  In comparison, the average daily trans-fat intake for Americans is 5.8 grams per day!  If you are a biochemistry-dork like me, read more about the structure of trans-fat at the full engagement center.

Major food sources with trans-fats from USDA’s facts on fats

Introducing trans-fats

The structure of a trans-fat reveals why it affects our health so negatively.  Every cell in our body had a thin fat layer that acts as a container for all of the cellular contents.  The fat layer around these cells is called the lipid bilayer membrane.  The lipid bilayer consists of two types of fatty acids found in nature:

  1. Unsaturated fatty acids (plant fats)
  2. Saturated fatty acids (animal fats)

At room temperature, unsaturated fatty acids are liquid while saturated fatty acids are solid.  The lipid bilayer functions optimally when it has a liquid-like consistency, coming from unsaturated fatty acids.  Some of the lipid bilayer needs some saturated fatty acids to keep it intact.

As mentioned above, a trans-fat (i.e., trans-fatty acid) is a man-made fat whose goal is to keep fats rock solid.  The trans-fat has no place in the lipid bilayer since it packs molecules together, versus allowing fluids to move in and out.

What this means nutritionally…

To make sure cells remain healthy and intact, we must have the right balance of unsaturated and saturated fats in the diet.  We want to eat lots of unsaturated fatty acids (olive oil, canola oil, avocado, nuts, seeds and fish) some saturated fatty acids (butter, cheese, meats) and little to no trans-fatty acids (cakes, cookies, pies and the like).  An easy way to look at this is by thinking of a stop light and what the colors mean:

  • GO: Unsaturated Fats
  • SLOW: Saturated Fats
  • WHOA!: Trans Fats

What this means structurally…

And now, the fun stuff.

Fats are all made up of these long chains of carbons (they sort of look like this: C-C-C-C-C-C-C-C).  To attach the carbons together, the body makes bonds (depicted in my example above as hyphens between the C’s).  Those bonds can either be single bonds (C-C) or double bonds (C=C).

  • SATURATED (C-C-C-C): When carbon chains are connected by single bonds only, it is considered saturated (animal products: butter, cheese, meat).
  • MONO-UNSATURATED (C=C-C-C):  When carbon chains are connected by one double bond, but the rest are single bonds, it’s considered monounsaturated (plant products: olive oil, canola oil, avocado).
  • POLY-UNSATURATED (C=C-C=C): When there is more than one double bond in the carbon chain, it’s considered polyunsaturated (animals and plants: omega-6 & omega-3 fatty acids, found in flaxseeds, walnuts and fatty fish).

Trans-fat configuration

Double bonds reduce the number of hydrogens per carbon, causing the hydrogens to shift to one side.  With less hydrogens, the fat is “unsaturated” with hydrogens – making the fat liquid at room temperature (think: awesome for the bilipid membrane).  But…

What happens to this type of monounsaturated or polyunsaturated fatty acid under high pressures and temperatures is that the liquid vegetable oil becomes rock hard, mimicking the texture of saturated fats.  This is called partial hydrogenation.

Why did we decide to make trans-fats?

Saturated and unsaturated fats are more prone to becoming rancid when left for a long time at room temperature, which is why trans-fats were developed.  As well, vegetable oil is a lot cheaper than lard, butter, beef tallow – as a result, cheaper products that last for long periods of time could be manufactured to the public.

The technology of trans-fats allowed for food products to remain on the shelf for longer periods of time, since they’d be less likely to spoil.  It’s only recently (within the last 20 years) that trans-fat has been reevaluated and linked to terrible health effects.

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