The media often report how bad trans fats are for you. The culprit for weight gain or obesity has often been laid at the door of fats generally especially saturated fats but the general consensus is that trans fats are the main issue. Recent evidence suggests that saturated fats have not as great a role to play in metabolic conditions as originally thought.
The name ‘trans fats’ is shorthand for trans-unsaturated fatty acids or trans fatty acids (TFAs).
Trans fats are synthesised when edible fats and oil are processed using full or partial hydrogenation . The intention is to make the oil more solid in what is known as hardening. This generated a cheap alternative to natural trans fats with better shelf life and suitable for cooking and frying.
Many fats contain carbon-carbon double bonds and are termed unsaturated. They become saturated when the double bonds are replaced with carbon-carbon single bonds. In some cases partial hydrogenation turns certain double bonds from the cis bond configuration to a trans configuration. A number of products of hydrogenation are produced. Oleic and linoleic acids are typical examples and each can produce over 20 different stereoisomers. They can make up 40% or more of the total fat content (Ascherio and Willett, 1997). A major fatty acid of industrially manufactured monounsaturated TFAs (Mensink, 2005) is elaidic acid (t18:1n9).
TFAs do occur in nature but only in small amounts. They have been found in milk, butter, and beef fat. They are also produced by isomerases of ruminant bacteria that can convert the double bonds of dietary fats into a trans configuration (Christiansen et al., 1997).
They are industrially important as food ingredients and are found in:-
– baked goods like pie crusts
– biscuits and crackers
Health And Trans Fats
Trans fats are considered to be unhealthy although they are source of food and nutrition. It is estimated that TFAs form just over 7% of all dietary fat forming 3% of the total energy intakes (Emken, 1984). The greatest risk is associated with poor heart health (Stender & Dyerberg, 2004). Other associations include formation of abdominal obesity (Koh-Banerjee et al., 2003).
Diabetes And Trans Fats
There is no clear relationship or association between diabetes and trans fats. One major study by the Department of Nutrition at the Harvard School of Public Health in Boston assessed the diet and lifestyle of over 80,000 women in relation to diabetes. They found that those who consumed the most trans fats appeared to have a 40 per cent increased risk of diabetes (Hu et al., 2001) but there are so many other factors to consider that have greater impact on development of the disease that it is not as relevant as it seems.
Better controlled studies demonstrate similar levels of inconsistency in their association between trans fats and diabetes.
Most of the studies with clearer associations have been conducted in animals but these are still with animals and not with humans.
This health issue was recognised in 2006 when the Food and Drug Administration requested manufacturers of any food product to require declaration of the TFAs presence. The amount was then to be stated on the ingredient label.
Ascherio, A., Willett, W. C. (1997) Health effects of trans fatty acids. Am. J. Clin. Nutr. 66 pp. 1006S–1010S
Christiansen, E., Schnider, S., Palmvig, B., Tauber-Lassen, E., Pedersen, O. (1997) Intake of a diet high in trans monounsaturated fatty acids or saturated fatty acids. Effects on postprandial insulinemia and glycemia in obese patients with NIDDM. Diabetes Care 20 pp. 881–887
Emken, E. A. (1984) Nutrition and biochemistry of trans and positional fatty acid isomers in hydrogenated oils. Annu. Rev. Nutr. 4 pp. 339–376
Hu, F. B., Manson, J. E., Stampfer, M. J., Colditz, G., Liu, S., Solomon, C. G., & Willett, W. C. (2001). Diet, lifestyle, and the risk of type 2 diabetes mellitus in women. New England Journal of Medicine, 345(11), pp. 790-797 (Article).
Koh-Banerjee, P., Chu, N. F., Spiegelman, D., et al. (2003) Prospective study of the association of changes in dietary intake, physical activity, alcohol consumption, and smoking with 9-y gain in waist circumference among 16, 587 US men. Am. J. Clin. Nutr. 78 pp. 719–727
Mensink, R. P. (2005) Metabolic and health effects of isomeric fatty acids. Curr. Opin. Lipidol. 16 pp. 27–30.
Stender, S., Dyerberg, J. (2004) Influence of trans fatty acids on health. Ann. Nutr. Metab. 48 pp. 61–66