What are trans fatty acids?

One of the most common questions I get in family practice is about fats in the diet. While I spend a lot of time discussing saturated and unsaturated fats, rarely am I asked about trans-fatty acids.

Since the New England Journal of Medicine released a study in 1997 we have realized that trans fatty acids are at least as important as saturated fats in the fight against heart disease.

Fatty acids are essentially a chain of carbon atoms (C) with hydrogen (H) attached to them. Each carbon atom can attach to four other atoms by means of a "bond". Sometimes the attachment is by a "double bond" and only has three other atoms connected to it.

When every carbon atom has four single bonds it is a SATURATED FATTY ACID. When even one carbon atom has less than four single bonds, i.e. two single and one double bond, it is an UNSATURATED FATTY ACID

Naturally occurring unsaturated acids are predominately CIS UNSATURATED. This means that the hydrogen on the carbon atoms next to the double bond are on the same side causing a bend. Because of the bend, this type of fat tends to be liquid at room temperatures.

The food industry obviously does not want liquid fat in their crackers, cookies, pastries, cakes, snack chips, imitation cheese, and candies. And, health conscious America did not want saturated fats, so they changed the shape of the fatty acid by "HYDROGENATION". This is a high temperature process whereby hydrogen is added using a chemical catalyst. During this process they can move the missing hydrogen positions to make a straight, TRANS UNSATURATED fatty acid molecule.

This type of fatty acid has a melting point of 44° C, which is above room temperature. Compare that to cis-fatty acid which melts at 13° C and saturated fatty acids which melt at 72° C. Unfortunately, these artificial fatty acids also become part of our bodies cells and membranes.

A very small amount of trans fatty acids exists naturally in nature. Some plants such as pomegranates, peas, and cabbage. Bacteria in the digestive tract of cows and other grazing animals ferment the food and creates a small amount of trans acids. We then eat them in the form of meat and dairy products which is about 3-5% trans.

Margarine's contain 11-49% trans fatty acids, while some cooking oils can have even higher amounts. Soft margarine has lower levels that stick margarine's. Our fast food diet of doughnuts, fried chicken, french-fries, chips, etc. have 35-38% of trans fatty acids.