The Trans Fat Spat

There is big news this week from the FDA who has banned the use of trans-fat in the entire food industry. I thought this would be an appropriate time to discuss the different types of fats we see on our food labels, and why the heck trans-fat got the snub.

Fatty acids that you and I eat have a couple defining chemical characteristics. One side of the molecule is the fatty part and one side of the molecule is the acid part – pretty convenient. Here is a representation of a fatty acid molecule:

 

 The fatty acid chain as it is called is made up of a long string of carbon and hydrogen atoms. The type of bonds between the carbon atoms determines whether a fatty acid is saturated or unsaturated. The fatty acid above is saturated because the fatty acid chain contains only single bonds between carbon atoms. Another way to think about saturated and unsaturated fats is to talk about the number of hydrogen atoms bonded to the carbon chain. Saturated fats have the maximum number of hydrogen atoms bonded to the carbon-chain, like the molecule above. In these terms then, unsaturated fats have fewer than the max number of hydrogen atoms bonded to the carbon chain, like the molecules below.

The number of hydrogens bonded to the chain is a direct result of the type of bonds between carbon atoms, so really the two concepts are intertwined. But in the two molecules above, you can see that each double-bonded carbon atom is only bonded to one hydrogen atom instead of two. These are both unsaturated fats.

Now that we’ve got that straight we can think about the difference between the unsaturated chain on the left and the unsaturated chain on the right. They both have the same number of carbon and hydrogen atoms but their shapes are drastically different. Cis and trans are labels that refer to the orientation of the hydrogen atoms which are near a carbon-carbon double bond. In a cis fatty acid, both hydrogen atoms are on the same side of the chain, resulting in a kink in the chain. In a trans fatty acid the two hydrogen atoms are on opposite sides of the chain and the shape remains relatively linear.

So what? Why is being a trans fatty acid such a crime? It has to do with the way fatty acid chains interact with one another. Groups of trans-fatty acids will pack in neat and tight rows because their chains are straight. Intermolecular forces between the chains make the clump of trans-fatty acids really dense and relatively difficult to break up. On the other hand, when cis-fatty acids clump together the kinks in their chains prevent them from getting too close to one another. This is why cis-fatty acids tend to be liquids at room temperature (most plant oils like olive or vegetable oil) and trans-fatty acids form solids at room temp (lard and most animal fats).

Fats in our bodies do similar things. Once trans-fatty acids get stored they are harder to break apart and thus harder to “burn off” during your exercise routine. They also integrate themselves into all of your cell membranes and undermine the fluidity and flexibility that the cell normally gets from cis-fatty acids. Perhaps most worrisome though is the effect they have on the fat-profile of your blood. We’ve all been warned about cholesterol and triglycerides. The amounts of these types of fats in our blood are directly affected by the types of fats we eat, and there is plenty of research to support the claim that trans-fatty acids do the worst damage.

So I would like to give a big shout out to the FDA for a making a change we can all be excited about, unless you’re a fan of Crisco…

Sources and further reading:

Huffington Post article: http://www.huffingtonpost.com/2013/11/07/fda-ban-trans-fats_n_4232871.html?utm_content=buffer5bdb2&utm_source=buffer&utm_medium=twitter&utm_campaign=Buffer

Mensink, R.P. and Katan, M.B. Effect of Dietary trans Fatty Acids on High-Density and Low-Density Lipoprotein Cholesterol Levels in Healthy Subjects. N Engl J Med 1990; 323: 439-445.

The Kinds of Fats and Why it Matters to You. Science Outreach: Food and Nutrition, Indiana University Dept of Biology, 2013. accessed here <http://www.indiana.edu/~oso/Fat/trans.html>

Ascherio, A.; Stampfer, M.J.; and Willett, W.C. (1999) Trans Fatty acids and coronary heart disease. Department of Nutrition and Epidemiology, Harvard School of Public Health. Accessed here http://www.drtimdelivers.com/EEasy122605/Harvardtransfats/transfats.html

Background image from: http://www.worldofmolecules.com/foods/trans_fatty_acids.htm