WHICH FAT OR OIL?
There’s nothing as controversial in human nutrition as dietary fats. Decades ago, trans fats and their relation to cardiovascular disease were the hot topics of discussion… until they were eclipsed by the incredible finding that olive oil could solve everyone’s LDL problems… a euphoria that crashed when other researchers found that this wasn’t always the case and what people really needed to do was to consume polyunsaturated fats instead (such as found in corn, peanut and sunflower oils and in fish)… and then other researches discovered that consuming polyunsaturated fats wasn’t enough in itself, and that people really ought to reduce their dietary intake of saturated fats as well (and hence the appearance of the saturated fat content on the nutritional labels of processed foods)… and finally, in December 2006 New York City banned trans fats from its restaurants, bringing them back into the limelight and onto nutritional labels.
What are Trans fats?
First let’s look at fatty acid chemistry.
Saturated fatty acids lack double bonds. The structure of caproic acid is given at the left. The entire carbon chain between the terminal methyl and carboxyl groups of this fatty acid has as many hydrogen atoms as can possibly be bonded to the carbon atoms. Thus the fatty acid is said to be “saturated”. With the exception of those fatty acids of 7 carbons or less, saturated fatty acids are solid at room temperature.
When a double bond exists between two carbon atoms the hydrogen atoms can assume either one of two configurations: cis, in which both hydrogen atoms appear on the same side of the double bond or trans, in which they appear on opposite sides. Geometrically, cis double bonds put a slight kink in the carbon chain whereas trans double bonds maintain its linearity: a change in geometry can change the function or metabolism of the fatty acid. Most of the naturally occurring fatty acids possess the cis configuration.
Fatty acids are present in our diet in the form of glycerides, that is, fatty acids linked to a molecule of glyercol. A triglyceride is composed of one molecule of glycerol and three molecules of fatty acids. When one of more of these fatty acids has a double bond in the trans configuration we call this a trans fat.
Which foods contain trans fats?
Naturally occurring trans fats can be found in the flesh and milk of ruminants such as cows, goats, and sheep. These are produced by the micro flora in their digestive systems. Estimates on the contribution of these trans fats to the diet vary from “minute amounts” to 15-20% of total trans fat intake. A much more important source of dietary trans fats is the variety of processed foods available in supermarkets which contain partially hydrogenated vegetable oils, as well as margarine, vegetable shortening and similar products. The naturally occurring trans fats have not been shown to share the harmful properties of synthetic trans fats resulting from the hydrogenation process (see “Naturally occurring trans fats” and “ Where are trans fats found?”, tfx.org.uk).
It is thus very important to check the ingredients listed on the labels of the processed foods you buy, watching out for “partially hydrogenated vegetable oil, vegetable shortening, and margarine”. These ingredients can be found in a variety of processed foods such as: mixes for cakes, cookies, biscuits and desserts; commercial bakery products such as pies, cakes, and doughnuts; some snacks (potato chips); gravy and sauce mixes; artificial creamers; cake frostings and confectionery; and even in some breakfast cereals. Fortunately, new regulations require manufacturers to list the content of trans fats on the nutritional labels of their products.
One must be particularly careful with canola/rapeseed oil, either for use as a vegetable oil in your home or as an ingredient in a food product. According to processing conditions, it can contain up to 4.6% trans fat (see “Where are trans fats found?”, tfx.org.uk) which may not be reported on the nutritional label.
So why hydrogenate oils in the first place?
Hydrogenation is a chemical process by which hydrogen atoms are added to double bonds to convert vegetable oils from a liquid to a semisolid (partially hydrogenated) or solid (hydrogenated) form. Noticing that hydrogenated cottonseed oil looked and behaved like lard, Proctor & Gamble began selling it in the USA in 1911 as a substitute for lard under the brand name “Crisco” (see “What are trans fats?”, tfx.org.uk). Relatively low cost, the rising popularlity of margarine during the second world war as a replacement for rationed butter and the promotion of margarines as a supposedly healthier alternative to animal fats or the tropical vegetable oils such as coconut and palm oils, all contributed to maintaining a market for hydrogenated vegetable oils.
Then there is the special case of industrial frying in which the oil is reused/ recycled in the fryers. Unsaturated fats can degrade to give a variety of compounds that can change the flavor of the fried foods and polyunsaturated fats can even given rise to a toxic compound called malondialdehyde. Partially hydrogenating the frying oil minimizes these reactions and health risks but unfortunately also increases the content of trans fat in both the oil and the fried food.
What are the health risks of synthetic trans fats?
Amongst some of the health risks attributed to dietary trans fats are:
- Elevation of LDL (“bad” cholesterol) and lowering of HDL (“good” cholesterol) levels.
- Promotion of the formation of arterial plaque.
- Decrease in the response to insulin.
- Reduction in the elasticity of blood vessels.
- Potential induction of allergies and a topic disorders.
For more information on trans fats and human health, please see “Trans fats and health –introduction” and “Trans fats and allergy, a topic disorders and other adverse reactions at tfx.org.uk.
What are the alternatives to Trans fats?
Among possible alternatives are: butter, butter fat (or ghee, basically butter with the water and proteins removed) and animal fats (remember that these contain natural trans fats which are considered not to endanger health in the concentrations at which they are present and given their metabolism in our bodies), coconut and palm oils, fully hydrogenated vegetable oil, and traditional vegetable oils (such as corn, peanut, soy, and sunflower).
Look for these alternatives on the labels of processed foods to avoid the health risks arising from the ingestion of trans fats.
I strongly recommend tfx.org.uk as a source of reliable information on Trans fats. Also useful is Dr. Mike Magee’s “Is it good fat or bad fat?” at HealthPolitics.org.
MJ Koziol, R&D, The Exotic Blends Co.