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Trans fatty acids

Presentation, sources and effects on health

Studies have shown that an excessive consumption of trans fatty acids is associated with an increase in cardiovascular risk. More details on these substances and ANSES recommendations are given below.

What are trans fatty acids?

Trans fatty acids are unsaturated fatty acids, for which at least one double bond is in a trans position, unlike unsaturated fatty acids that are synthesised by the body and whose double bonds are in a cis position.

Where do trans fatty acids come from?

Trans fatty acids can come from two distinct origins:

  • some trans fatty acids are said to be natural. They are produced in the stomach of ruminants (cows, sheep) by resident bacteria. These fatty acids are then incorporated into the body fat and milk of animals. They are consequently found in meat, milk and dairy products;
  • other trans fatty acids are technological in origin. They are synthesised through industrial processes such as hydrogenation of plant oils. This type of process is used to transform fats from a liquid to a solid state, which facilitates their use and storage and makes them less sensitive to oxidation;
  • trans fatty acids can also form during heating and cooking of plant oils at a high-temperature whether during industrial processing or household use of the oils.

Which products contain trans fatty acids?

The main food vectors for intake of natural trans fatty acids are dairy and meat products.
Trans fatty acids which have a technological origin are used in the agrofood industry as stabilisers and preservatives. They make food firmer and more stable and hence less likely to go rancid. They are also found in many processed food products such as croissant¬-like pastries, pizzas and quiches.

Industrial bread and bread products, croissant-like pastries and biscuits are thus ranked second amongst foods which contribute to intake of trans fatty acids. Other contributing products include margarine, which is widely used, chocolate bars and some precooked ready-made dishes.

What effects do trans fatty acids have on health?

Epidemiological studies have shown that an excessive consumption of trans fatty acids (intakes greater than 2% of total energy intake) is associated with an increase in cardiovascular risk. These damaging effects lead to an increase in "bad" cholesterol (low-density lipoprotein or LDL) and a decrease in "good" cholesterol (high-density lipoprotein - HDL).

However no increase in cardiovascular risk has been demonstrated with the consumption of natural trans fatty acids at levels of consumption which have recently been observed in France.

Conversely an increased risk of cardiovascular events has been associated in epidemiological observations and cohort studies with the consumption of total trans fatty acids and trans fatty acids of technological origin and at high concentrations (more than 2% of total energy intake (TEI) and more than 1.5% of the TEI, respectively).

Intake of the French population

In 2005 in a report entitled "Health risks and benefits of trans fatty acids found in food - Recommendations", the Agency set a maximum intake threshold for trans fatty acids to 2 % of the TEI, irrespective of age and gender, for both children and adults. This threshold corresponded to an intake level which would lead to an increased risk of cardiovascular disease. In addition the Agency evaluated the intakes of the French population in trans fatty acids on the basis of the INCA 1 survey data. The mean intakes of the population for trans fatty acids corresponded to 1.3% of total energy intake. In adults, the consumption levels of 5% of the population reached the maximum threshold. The age group which consumed the most was that of boys from 12 to 14 years old. They absorbed almost 8 g per day of trans fatty acids and exceeded the threshold corresponding to an increased risk of cardiovascular disease.

In 2008, the Agency brought this work up to date using the diet data collected for the INCA 2 survey (2006/2007) and for the drawing up of a new nutritional composition table for food.

Even though the simulation methodologies used in 2005 and 2008 were different, the Agency considers that the intake levels estimated in 2008 were lower than those observed in 2005.

In adults the intakes of trans fatty acids mostly come from natural compounds. In children, an equivalent distribution between natural trans fatty acids and those having a technological origin has been observed.

In gross value, the intakes of trans fatty acids are higher on average in adults than in children. However the mean intakes in proportion to total energy intake are similar in adults and in children and are close to 1%.

For the highest consumers, the intakes remain lower than the 2% TEI  threshold set in 2005, irrespective of age and gender, for both children and adults.

The Agency's recommendations

Even though the observations made in 2008 showed a decrease in intakes, the Agency does not bring into question its 2005 recommendations, which aim to limit the population's intake of trans fatty acids.

Furthermore, the Agency emphasises that technological trans fatty acids are found in foods for  technical-functional reasons. Consequently it encourages efforts to reduce the use of these trans fatty acids, which are already being used by professionals, both for human and animal food, in order to reduce the risk of exposure. Alternatives to the use of trans fatty acids for their technical-functional properties should thus be envisaged.