Aspartame (E951)

What is aspartame and what is it used for?

Aspartame is a sweetener formed from two amino acids (aspartic acid and phenylalanine). Gram for gram it contains a similar number of calories to sugar; but because it is very sweet, it is used in very small amounts, so its contribution to energy is negligible.

During digestion it is broken down into its components (aspartic acid, phenylalanine and a small amount of methanol). These substances also occur naturally in food; for example, some fruit and vegetable juices can contain as much methanol as an aspartame-sweetened drink, or more. Because it is not heat-stable, it is rarely used in baked products.

Which products contain it?

• Diet, light and “sugar-free” fizzy drinks
• Sugar-free chewing gum and sweets
• Tabletop sweeteners (tablets and powder)
• Some yoghurts, milk desserts and flavoured waters
• Chewable vitamins and some medicines

What do the IARC 2B and JECFA decisions say?

In 2023 two separate WHO-linked bodies assessed aspartame. IARC placed aspartame in Group 2B, noting that there is limited evidence in humans and animals. IARC's assessment shows the strength of the evidence on whether a substance can cause cancer; it does not say how much consumption would pose a risk.

JECFA, which carries out risk assessment, concluded that the available data did not require a change to the acceptable daily intake (ADI) and kept the limit of 40 mg per kilogram of body weight per day. According to the WHO's statement, an adult would have to drink a large number of cans of diet drinks every day to exceed this limit. In the EU, EFSA uses the same ADI value.

In 2023 the WHO also published a guideline that does not recommend using non-sugar sweeteners for weight control; this recommendation covers all sweeteners, not just aspartame.

The phenylketonuria (PKU) warning

Phenylketonuria is an inherited disorder in which the body cannot break down the amino acid phenylalanine. A build-up of phenylalanine can damage the nervous system, especially in children. Because aspartame contains phenylalanine, these people need to avoid it. In the EU and Türkiye, the labels of products containing aspartame must carry the warning “contains a source of phenylalanine” or “contains aspartame (a source of phenylalanine)”, depending on whether aspartame is listed in the ingredients by name or by its E number.

What to do when you see it on a label

If you don't have phenylketonuria and your consumption is reasonable, there is no need to worry about a product containing aspartame. Using diet drinks as a stepping stone away from sugary drinks can make sense; in the long run, however, the best drink is water. For a comparison of sweeteners, see the sucralose and acesulfame K pages.