The health risks of eating trans fats

DR PAULINE BALAC

Senior biology lecturer, School of Applied Sciences, University of Huddersfield

AN editorial in the British Medical Journal this month, by two professors of medicine at Harvard Medical School, calls for the removal of all industrial trans fats from food.

They state that a strategy to reduce consumption of industrial trans fats by even 1 per cent of total energy intake could prevent 11,000 heart attacks and 7,000 deaths each year in England.

But what are trans fats, how and why they are produced, what are the dangers of eating them and how can we avoid consuming them?

Since the Second World War, the industrial hydrogenation of liquid oils to produce margarines and shortenings has provided a cheap, vegetarian alternative to butter and lard.

The process of hydrogenation, in relation to vegetable oils, makes them into partially saturated fats. These have a higher melting point, which makes them more useful for baking. The partial saturation also extends their shelf-life, preventing the fat from becoming rancid. Complete hydrogenation converts the fat into a saturated or hard fat.

Trans fatty acids are produced as a by-product when these vegetable oils are partly hydrogenated. The fat has the physical properties of a saturated fat, but the body is unable to properly metabolise these trans fatty acids.

Trans fatty acids are rare in most natural diets, with just a small amount found in the meat and milk of cows, sheep and goats, produced by bacteria in their rumens. These trans fats probably contribute no more than 0.5 per cent of total energy intake.

One of the health risks of consuming trans fats are that they lower levels of the “good” cholesterol and raise levels of the “bad” cholesterol. Consumption of trans fats is therefore associated with a substantial risk of heart disease. This risk is much higher per calorie than for any other major dietary nutrient, including saturated fats.

Commercial sources of trans fats include baked goods, deep fried foods, packaged snacks, margarines and shortenings.

In developed nations, the average population consumption of trans fats is estimated to be 2-4 per cent of total energy intake. However, there may be certain population groups who consume as much as 6-8 per cent of total energy intake.

In 2003, Denmark became the first country to introduce laws to control the sale of foods containing trans fats. A year later Canada banned the use of trans fats in foods altogether.

In 2006, it became law in the USA to list the content of trans fats on food labels, if present at more than 0.5g per serving. That same year, New York City also banned many trans fats from its restaurants, which prompted similar bans in other parts of the USA.

In the UK, at the beginning of 2010, in readiness for the general election, the Faculty of Public Health and the Royal Society for Public Health jointly published a manifesto listing “12 steps to a better public health”.

One of the proposals is to stop the use of trans fats by 2011.

The Food Standards Agency has responded by saying that the UK’s low average consumption of trans fats makes a complete ban unnecessary.

However, if you are worried about the health risks of eating trans fats, you can do something to avoid consumption.

In the absence of any specific labelling, avoid all foods that list hydrogenated or partially hydrogenated fats or shortenings on their labels.

When cooking at home use liquid vegetable oil for frying and only margarines or shortenings that are labelled trans fat free.

Many margarines and vegetable shortenings in supermarkets now show the products as “virtually free of trans fats”.

You may also be able to check these details with restaurants or take-aways.

Heart healthy fats to consume are olive oil, corn oil, sunflower oil and other seed oils. The best way to eat them is drizzled over a salad with some lemon juice.