What is it?
Aspartame is a man-made sweetener made by joining two amino acids, aspartic acid and phenylalanine, with a small amount of methanol attached. It adds almost no calories because so little is needed.
E-numbers / Sweeteners / E951
Aspartame
also: NutraSweet · Canderel · Equal · APM
A man-made sweetener about 200 times sweeter than sugar, used in diet drinks and sugar-free foods. The WHO's cancer agency lists it as a possible cause of cancer.
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Carbonated Water, Colour (E 150d), Sweeteners (Aspartame, Acesulfame K), Natural Flavourings, Caffeine Flavouring, Acids (Phosphoric Acid, Citric Acid)
E951
Aspartame
The WHO's cancer agency rates it a possible cause of liver cancer, based on limited evidence in people.
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UK supermarket foods that declare E951: 562 of the 43,325 we checked (1.3%)
Counted by its code or its name in the ingredient list.
Only 1.6% of these labels print “E951”. Most use the name: look for “aspartame”.
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
How common it is in UK food, by aisle
- Soft drinks and juices366 products14% of 2,627
- Chocolate and sweets60 products2.9% of 2,045
- Fruit, vegetables and salad43 products1.6% of 2,631
- Yoghurt, milk and dairy26 products1.1% of 2,273
What aspartame is, what it does and where you will see it
Why it’s worth knowing. The WHO's cancer agency rates it a possible cause of liver cancer, based on limited evidence in people. People with the inherited condition phenylketonuria must avoid it, because their bodies cannot process one of the substances it breaks down into.
What does it do?
It tastes about 200 times sweeter than sugar, so very little replaces sugar without the calories. In the body it breaks down into phenylalanine, aspartic acid and methanol.
Where you will see it
Diet and zero-sugar fizzy drinks, sugar-free squash and chewing gum, low-calorie yoghurts and desserts, and table-top sweeteners. Labels call it aspartame or E951, and packs must also say contains a source of phenylalanine.
What the science says
The WHO's cancer agency calls it a possible cause of cancer
In 2023 the WHO's cancer agency reviewed aspartame for the first time and put it in its possibly causes cancer group, based on limited evidence in people linking it to liver cancer.
The WHO's cancer agency (IARC) classed aspartame as Group 2B, possibly causing cancer in humans, based on limited evidence for liver cancer.
2023Cancer classificationIARC / WHO press release
The WHO's food additives committee, reviewing it at the same time, kept the daily limit of 40mg per kg of body weight.
2023Regulator reviewJECFA / WHO
A large French study linked higher intake to more cancer
A large French study that followed more than 100,000 adults found that people who ate more artificial sweeteners, aspartame among them, had slightly more cancer overall, and more breast and obesity-related cancers.
Among 102,865 French adults, higher aspartame intake was linked to a slightly higher risk of cancer overall (15% higher) and of breast cancer (22% higher).
2022Observational study in peopleDebras et al., PLOS Medicine (NutriNet-Sante)
The daily limit rests on animal studies
UK and EU regulators set a daily limit of 40mg per kg of body weight, based on long-term animal studies.
European reviewers' 2013 review set the daily limit at 40mg per kg of body weight.
2013Regulator reviewEFSA Journal, re-evaluation of aspartame (E 951)
People with phenylketonuria must avoid it
Aspartame releases phenylalanine as it breaks down. People born with phenylketonuria (PKU) cannot break phenylalanine down properly, so it builds up and can harm the brain. That is why every product with aspartame must warn that it is a source of phenylalanine.
In the gut aspartame is fully broken down into phenylalanine, aspartic acid and methanol. The phenylalanine released is a risk for people with phenylketonuria.
2013Established factEFSA Journal, re-evaluation of aspartame (E 951)
Where it stands with the regulators
Permitted as a sweetener in Great Britain and the EU
Daily limit. 40mg per kg of body weight a day (European reviewers 2013, confirmed by the international committee 2023).
- Legal basis
- Allowed under UK additive law, with a compulsory phenylalanine warning on the label. It is on the Food Standards Agency's approved list.
- Permitted foods
- Diet and reduced-sugar soft drinks · Sugar-free chewing gum and sweets · Low-calorie yoghurts and dairy desserts · Reduced-energy foods and table-top sweeteners · Sugar-free squash and cordials
- Maximum levels
- Depends on the food, roughly 25 to 6,000mg per kg. Table-top sweeteners follow separate rules.
- History
- European reviewers completed a full review in 2013 and kept the 40mg per kg daily limit. In July 2023 the WHO's cancer agency classed it as possibly causing cancer (Group 2B), while the international committee kept the daily limit unchanged. The contains a source of phenylalanine warning has long been compulsory for people with phenylketonuria.
Who should be careful
Anyone with phenylketonuria (PKU) must avoid it, including children picked up by the newborn heel-prick test. Look for aspartame, E951 or contains a source of phenylalanine on the label.
The honest read
Two official verdicts from 2023 pull in different directions, and both are real. The WHO's cancer agency rated aspartame a possible cause of cancer on limited evidence in people, while the WHO's food additives committee kept the daily limit unchanged. Observational studies link higher intake to a small rise in cancer, and the daily limit still rests mainly on animal studies. The disagreement is genuine and the research is ongoing. Both verdicts turn on how much someone takes in over time rather than any one drink, so if that is your question, it helps to track food additives across a normal week.
Common questions about aspartame
Is E951 banned in the UK?
No. Aspartame is permitted as a sweetener in Great Britain and the EU, with conditions of use and a compulsory phenylalanine warning on the label.
Does E951 cause cancer?
In 2023 the WHO's cancer agency (IARC) classed aspartame as possibly causing cancer in humans (Group 2B), based on limited evidence in people pointing to liver cancer. The WHO's food committee left the daily limit unchanged. The science is not settled.
What foods contain E951?
Diet and zero-sugar fizzy drinks, sugar-free chewing gum, low-calorie yoghurts and desserts, sugar-free squash and table-top sweeteners. Labels call it aspartame or E951, with a phenylalanine warning.
Is E951 vegan?
Aspartame is made from amino acids and does not come from animals, so it generally suits vegans. Check the rest of the product, which may not.
Sources
- Aspartame hazard and risk assessment results released, WHO/IARC/JECFA (2023)
- Scientific Opinion on the re-evaluation of aspartame (E 951) as a food additive, EFSA Journal (2013)
- Debras et al., Artificial sweeteners and cancer risk: NutriNet-Sante cohort, PLOS Medicine (2022)
- Approved additives and E numbers, UK Food Standards Agency
- Regulation (EU) No 1169/2011 on food information to consumers
Last reviewed: 9 November 2026
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