Learn about Trans Fats

There is growing evidence indicating that trans fats intake is linked to an increased risk of cardiovascular disease. The following fact sheet will provide you with brief information on this substance.

Formation of trans fats

All animal and plant sources of fats contain fatty acids, which can be saturated or unsaturated. In terms of chemical structure, trans fats are classified as unsaturated fats. They have one or more carbon-carbon double bonds in their configuration.

One of our main dietary sources of intake of trans fats is from food produced with hydrogenated vegetable oil. Vegetable oil, after the process called hydrogenation, will turn from liquid to semi-solid or solid form. If the hydrogenation goes to completion, there would be no trans fats. However some of the fat molecules in vegetable oil undergo partial hydrogenation and the double bonds remain in the structure. Thus trans fats are formed.

Sources of trans fats

Hydrogenated vegetable oils such as shortening and margarines are commonly used to produce or prepare bakery and fried products since they can increase the shelf life of the products, change the texture of the food and are usually lower in cost.

We may also intake trans fats from natural sources. For example, small amount of trans fats are naturally present in milk and fat of cow and sheep.

Potential risk of trans fats intake

Generally, saturated fats are known risk factors for coronary heart disease since they increase low density lipoproteins (the 'bad' cholesterol) in blood. Trans fats, however, tend to raise the level of low density lipoproteins while lowering the level of high density lipoproteins (the 'good' cholesterol). These changes in blood lipids (cholesterol levels) may increase the risk of heart disease.

Recommendation from World Health Organization

Currently, there is no international consensus on the regulatory control on trans fats, including its labelling. Dieticians generally recommend the use of non-hydrogenated oils such as canola or olive oil whenever possible. The World Health Organization and the Food and Agriculture Organization of the United Nations suggest that diets should provide a very low level of trans fats, i.e. an intake of less than 1% of daily energy intake. For example, an individual with a daily energy intake of 2 000 kilocalories should limit the intake of trans fats to less than 2.2 grams per day.

Situation in Hong Kong

To facilitate consumers to make healthy food choices in Hong Kong, all prepackaged foods applicable to the governmental regulations shall declare the trans fats content on labels. The 'Trans fats free' claim will also be permitted if the following conditions are satisfied: (1) not more than 0.3 gram trans fats per 100 grams or millilitres of food; (2) not more than 1.5 grams saturated and trans fats per 100 grams of food or not more than 0.75 gram saturated and trans fats per 100 millilitres of food; and (3) not more than 10% energy from saturated and trans fats.

Activities:

1. By using the information provided from the newsletter, calculate the energy provided by 1 g of fat, in kilocalories.

2. Suppose an adult requires 2 400 kilocalories per day, what is the upper limit of the intake of trans fat (in gram per day)?

Relevant Textbook Contents:

Topic 8 Chemistry of Carbon Compounds

Section 33.13