What are fatty acids?
Fatty acids bind to glycerol in molecular chains, and together form the building blocks of fats. These chains may:
- Vary in length – fatty acid chains are liquid when very short and become harder as their length increases.
- Be saturated or unsaturated – animal fats contain mostly saturated fats, as do coconut and palm kernel oil. Other vegetable oils such as sunflower, maize, soya, peanut, cotton, safflower, canola and olive, contain more unsaturated fats. These unsaturated fats can be further categorised into “mono” and “poly” unsaturates. Unsaturated fats are the types currently used in the production of margarine. (See note at the end of the article for more information on unsaturated fats.)
- Be found in two forms: cis or trans. Most unsaturated fatty acids occur in the “cis” form in our food supply. The “trans” form constitutes only a small percentage of unsaturated fatty acids found naturally in food. Depending on the source, the molecular chains occur in various lengths and the fatty acids have different degrees of saturation. These two factors give the fats their characteristic properties.
What are trans fats or trans fatty acids?
Trans fats or trans fatty acids are unsaturated fatty acids that occur naturally in animal and dairy fats as a result of animal digestive processes. They are also produced in the margarine manufacturing process known as hydrogenation.
During these processes the unsaturated fat molecule undergoes a change in its structure from the more commonly occurring cis form to the less commonly occurring trans form. The unsaturated fat molecule remains unsaturated, but becomes harder and more similar to a saturated fatty acid in texture and in its ability to increase blood cholesterol levels.
Are trans fatty acids harmful?
There is evidence that trans fatty acids have a more negative effect on cholesterol levels than saturated fats; they not only contribute to a raising of total cholesterol levels, but also reduce the amount of “good” cholesterol in the blood. No conclusive evidence exists to suggest that these fats are harmful in the average diet. However, trans fats are not necessary nutrients in the diet. Therefore consumption should be decreased and manufacturers should minimise the presence of trans fatty acids in food products.
Why is there concern regarding trans fats?
In the past it was shown that saturated fatty acids (mainly found in animal fats) had a tendency to increase the bad LDL cholesterol in the blood – one of the risk factors associated with coronary disease. Hence, scientists advised the public to substitute unsaturated vegetable fats for saturated animal fats in the diet. However, recent research has shown that unsaturated trans fatty acids not only promote high levels of LDL cholesterol like saturated fatty acids, but in fact they may have an even higher tendency to do so than the natural saturated fatty acids! In addition the trans fatty acids also reduce levels of good HDL cholesterol in the blood.
Why are fats and oils hardened or hydrogenated?
Fats and oils are hydrogenated or partially hydrogenated to varying degrees. This makes them more useful in producing a variety of more acceptable, safe and appealing food products. Plant oils (in particular) are hydrogenated to:
- Produce fats with a range of different properties for a variety of end uses, for example:
- Partially hydrogenated frying oil can be used for potato chips to give them a longer shelf-life, because unsaturated or unhydrogenated oils can quickly become rancid or unsafe to eat.
- Margarine is a form of vegetable oil that is spreadable, directly from the fridge.
- Brick or hard margarine improves the texture, taste and appearance of cakes; oil does not produce cakes of acceptable quality because they are “greasy”.
- Provide the cheapest and most plentiful source of fats and oils. Hydrogenating plant oils makes it possible to substitute them for animal fats. Animal fats are more costly and increase the risk of coronary infraction more than plant fats especially at the high levels of consumption in western and many developing countries.
Do alternatives to hydrogenation exist?
Trans fats are only produced if fats and oils are partially hydrogenated. Totally hydrogenated products contain no trans components – so they may be blended with unsaturated fats and oils to achieve the desired properties and still be trans free. Similarly, liquid oils (such as sunflower) can be blended with naturally occurring harder fats (such as components of palm oils) to produce more stable frying oils, free of trans fatty acids. In both cases the effect is that saturated fats replace unsaturated trans fats in the final product. Since research into the effects of saturated/unsaturated fats is inconclusive, this blending process has caused further controversy.
What foods contain trans fats?
Trans fats constitute only a small percentage of fatty acids found in food products.
They are found in levels ranging from 2% to 9% in beef and mutton fat, dairy products and to a lesser extent in pork and poultry fat.
A major source of trans fatty acids in modern diets has been margarine and other baking, frying and ingredient fats, which may be included in products such as biscuits, crackers, flaky pastry, pies, cakes, confectionery, ice cream, fried snacks and fast foods. Some consumer-oriented producers have drastically reduced the content of trans fats in their margarines from earlier highs of 25% to levels of below 1 %.
Some companies voluntarily list trans values on their product labels. Legislation in this regard is likely to make clear labelling mandatory in the future, with levels under 0,5% trans fats being classified as trans fatty-acid free.
Trans fats are not found in plant products and are not found in consumer salad and frying oils.
How much is consumed?
In western-type diets, individuals are likely to consume about 3g of trans fats per day. One third of this may be derived naturally from dairy products and meat, the balance from fast foods, snacks, biscuits, cakes, chips, pies, etc, which contain partially hydrogenated fats. These levels should not pose a health risk, but increased consumption is not advised.
What Is The FACS Message?
Minimising trans fats in the diet is advised; read product labels, follow a prudent diet, and limit total fat intake to recommended levels.
The guideline regarding fats and oils is that the total intake, from all sources, should not provide more than 30% of an individual’s daily energy requirement. That intake should ideally consist of equal quantities of saturated, monounsaturated and polyunsaturated fats. As an indication, an average active man (79 kg) should not eat more than 97g of fat per day, and an average active woman (weighing 63 kg) 73g. Controlling total fat intake in this way is, in most cases, more appropriate than trying to eliminate trans fats from a diet altogether. Consumers should compare the nutrition labels of the products that are likely to contribute significant amounts of trans fatty acids to their diets, such as margarines and cooking fats. Today, the presence of trans fatty acids is often indicated on South African labels. However, consumers must look for other warning signs such as where the fat content of the product is high, or where partially hydrogenated fats and oils are listed as ingredients. In these instances, trans fats can be expected to be present unless otherwise specified. Choose products with the lowest percentages of partially hydrogenated fats or lowest total fat values declared on the labels. Take-away and fast-foods might also contain trans fatty acids; contact the relevant companies for information on their products.
For Your Interest
What’s an unsaturated fat?
A saturated fatty acid contains a full compliment of hydrogen atoms attached to the carbon chain. An unsaturated fat is short of the full compliment of hydrogen atoms. A monounsarurate is short of two hydrogen atoms, which means that somewhere in the fatty acid carbon chain there is a double bond between two carbon atoms. This double bond can exist in the “natural”, cis, or bent conformation, or the bond can exist in the “unnatural”, trans, or linear conformation. If a fatty acid is short of four or six or more hydrogen atoms it is know as “polyunsaturate” and the cis-trans isomerism can affect each one of the carbon to carbon double bonds.
F.A.C.S. Scientific Director. 2009.