E951 — Aspartame
Also labelled: Nutrasweet · Canderel · Aspartam
Aspartame is the most studied sweetener in existence, and the two bodies that looked at it most recently reached conclusions that sound contradictory but are not. Frela rates it high on precaution after the 2023 IARC classification — while being clear that food safety regulators did not change their intake limits.
At a glance
- E number
- E951
- Class
- Sweetener
- Origin
- Synthetic dipeptide of aspartic acid and phenylalanine
- EU status
- Authorised; products must declare a source of phenylalanine
- Acceptable daily intake
- 40 mg per kg of body weight per day (EFSA 2013, reaffirmed by JECFA 2023)
- Typically found in
- Diet soft drinks, sugar-free chewing gum, light yoghurt, tabletop sweeteners, some medicines
What it actually is
Aspartame is a dipeptide — two amino acids, aspartic acid and phenylalanine, joined together with a methyl group attached. It is roughly 200 times sweeter than sugar, so the quantities used are tiny, which is why it contributes almost no calories despite being metabolised like protein.
In the body it breaks down completely into aspartic acid, phenylalanine and a small amount of methanol. All three occur naturally in ordinary food; a glass of tomato juice delivers more methanol than a can of diet cola.
Why the phenylalanine warning exists
European labels must state that a product contains a source of phenylalanine. This is not a general safety warning. It exists for people with phenylketonuria (PKU), an inherited disorder affecting roughly one in 10,000 births in Europe, in which phenylalanine cannot be metabolised and accumulates to harmful levels.
Newborns in Germany and most of Europe are screened for PKU. For anyone without the condition, the warning carries no practical meaning.
The 2023 classification, read properly
In July 2023 two WHO bodies published on aspartame on the same day, and the coverage conflated them badly. IARC classified aspartame as Group 2B, possibly carcinogenic to humans, citing limited evidence from a small number of observational studies on liver cancer. JECFA, on the same day, reaffirmed the acceptable daily intake of 40 mg per kg of body weight, finding no convincing evidence of harm at realistic intakes.
These are answers to different questions. IARC performs hazard identification: could this substance cause cancer under some circumstance, at some dose? JECFA and EFSA perform risk assessment: is it likely to, at the amounts people actually consume? Group 2B is a broad category that also contains aloe vera leaf extract and traditional pickled vegetables.
For scale: a 70 kg adult would need to drink somewhere in the region of nine to fourteen cans of a typical diet soft drink every day, for life, to reach the ADI. Most people who consume aspartame regularly are nowhere near it.
Why Frela still rates it high
Frela's additive scale is deliberately more cautious than a regulatory ADI. An ADI answers 'is this safe at normal intake' — a question regulators have answered yes. Frela's rating answers a different one: 'how much unresolved concern is attached to this substance?'
A Group 2B classification from IARC is unresolved concern by definition, and Frela would rather be transparent about applying a precautionary standard than quietly pretend the classification does not exist. Someone who disagrees with that judgement has everything they need on this page to reach their own conclusion.
How Frela scores it
Frela rates E951 high risk, taking the additive component to its floor. Because Frela scores by the worst additive rather than the average, a diet drink containing aspartame will not recover that component through an otherwise innocuous ingredient list.
Note that a diet soft drink often scores better than its sugared version overall, because the nutrition component — built on the official Nutri-Score tables — responds strongly to sugar content. Frela does not decide for you whether sugar or sweetener is the better trade; it shows both effects separately so the trade is visible.
Common questions
Did the WHO say aspartame causes cancer?
No. One WHO body (IARC) said it is possibly carcinogenic based on limited evidence, which is a statement about hazard. Another WHO body (JECFA) simultaneously confirmed the existing safe intake level, which is a statement about real-world risk. Both statements stand.
Is aspartame worse than sugar?
They fail differently. Sugar has well-established effects on dental health, energy density and metabolic markers at habitual intake. Aspartame has a precautionary classification and no established effect at normal intake. Frela scores both and shows the components separately rather than declaring a winner.
Does aspartame break down when heated?
Yes, which is why it is rarely used in baking — it loses sweetness rather than becoming hazardous. The breakdown products are the same amino acids it is made from.
Sources
- WHO — Aspartame hazard and risk assessment results released (July 2023)
- EFSA — Scientific opinion on the re-evaluation of aspartame (E951) (2013)
- IARC Monographs Volume 134 — Aspartame, methyleugenol, isoeugenol
Last reviewed:
