Why aspartame keeps getting cleared and questioned at the same time
Aspartame is roughly 200 times sweeter than table sugar, so a pinch replaces a spoonful and adds almost no energy. Over 100 regulators have judged it safe within set limits. Yet in 2023 a cancer agency labelled it possibly carcinogenic, and US regulators publicly disagreed.
Discovered in 1965 and sold as NutraSweet, Equal and Canderel, aspartame is a methyl ester built from two amino acids, aspartic acid and phenylalanine. The US Food and Drug Administration approved it in 1974, briefly revoked that approval, and re-approved it in 1981. Gram for gram it releases about as much energy as sugar, 4 kilocalories, but so little is needed that the calories barely register. Its sweetness lingers, and tasters report bitter off-notes, so makers often blend it with acesulfame potassium.
Chemistry limits where it works. Heat or alkaline conditions break it back into amino acids, which makes it poor for baking. Dissolved in water at room temperature it lasts longest at pH 4.3, with a half-life approaching 300 days. Humans taste it through a receptor formed by the proteins TAS1R2 and TAS1R3; rodents find it unremarkable because their receptors differ. In the gut it is quickly split into methanol, phenylalanine and aspartic acid, so none reaches the blood intact even after doses above 200 mg per kilogram.
Regulators set the acceptable daily intake at 40 mg per kilogram of body weight in Europe and 50 in the US. A 12-ounce diet soda holds 0.18 grams, so a 75-kilogram adult would need about 21 cans a day to pass the American threshold. Because phenylalanine is dangerous for people with the inherited disorder phenylketonuria, US labels must carry a warning, and the UK and Canada require similar notices.
The debate sharpened in 2023. The World Health Organization advised against non-sugar sweeteners for weight control, citing no long-term fat loss benefit. In July the International Agency for Research on Cancer placed aspartame in Group 2B on limited evidence, while its lead investigator called this a prompt for more research. The Joint FAO/WHO expert committee saw no reason to change its intake limit, and the FDA said the underlying studies had significant shortcomings.
Source: Aspartame
