Aspartame vs Saccharin: which is worse?

What is Aspartame?

Aspartame is a low-calorie synthetic dipeptide sweetener composed of two amino acids — phenylalanine and aspartic acid — bonded with methanol. When metabolized, it breaks down into these three components. It is approximately 200 times sweeter than sucrose, so tiny amounts provide significant sweetness with almost no calories.

What is Saccharin?

Saccharin is the oldest artificial sweetener, discovered accidentally at Johns Hopkins in 1879. It is a sulfonamide compound approximately 300-400 times sweeter than sucrose with no caloric value. It has a slightly bitter metallic aftertaste at higher concentrations. Saccharin's sodium salt (sodium saccharin) is the form used in most food applications.

Documented risks

Aspartame: Aspartame has been one of the most studied food additives in history, with over 200 regulatory studies reviewed by multiple agencies. The FDA and EFSA have repeatedly reaffirmed its safety at permitted levels for the general population. IARC classification controversy (2023): In July 2023, IARC classified aspartame as Group 2B (possibly carcinogenic to humans), based primarily on limited evidence from human epidemiological studies associating aspartame intake with hepatocellular carcinoma (liver cancer) in some observational studies. Notably, the WHO Joint Expert Committee on Food Additives (JECFA) simultaneously re-evaluated aspartame and maintained the ADI at 40 mg/kg/day, concluding that the evidence does not establish that aspartame causes cancer at typical intake levels. This rare split between IARC (hazard identification) and JECFA (risk assessment) created significant public confusion. Phenylketonuria (PKU): Aspartame is definitively harmful for individuals with phenylketonuria — a genetic disorder affecting phenylalanine metabolism. People with PKU cannot process phenylalanine normally, and aspartame consumption can cause severe neurological damage. This is why all aspartame-containing products must carry a PKU warning on US and EU labels. Methanol release: aspartame metabolism releases methanol (~10% by weight). Critics including independent researcher Woodrow Monte have argued that methanol from aspartame is harmful, citing methanol's conversion to formaldehyde and formic acid in the body. However, methanol released from aspartame is a fraction of the methanol obtained from fresh fruit juices, and regulatory agencies consider the amounts released too small to be clinically significant. Gut microbiome concerns: a 2021 Cell study found that aspartame and other sweeteners altered gut microbiome composition and glucose tolerance in humans. These microbiome effects are an emerging area of research.

Saccharin: Saccharin's carcinogenicity history is one of the most tumultuous in food regulatory history. In 1977, the FDA proposed banning saccharin after studies found it caused bladder cancer in rats at very high doses. Congress passed the Saccharin Study and Labeling Act, which put a moratorium on the ban and required a cancer warning label on saccharin products ('Use of this product may be hazardous to your health. This product contains saccharin which has been determined to cause cancer in laboratory animals.'). By 2000, saccharin was removed from the US National Toxicology Program's Report on Carcinogens after subsequent research determined that the bladder cancer in male rats was caused by a rat-specific mechanism — high pH, high protein, and calcium phosphate in rat urine — that does not apply to human urine. The cancer warning label requirement was repealed. IARC also removed saccharin from its Group 2B list in 1999. However, Canada maintained its ban on food use saccharin, citing continued precautionary concern. A 2022 study in Cell found saccharin was among the artificial sweeteners most significantly altering gut microbiome composition and glucose tolerance in previously non-sweetener-using participants. Saccharin showed the largest effect on glucose tolerance among the sweeteners studied (saccharin, sucralose, aspartame, stevia). Saccharin passes through the placenta and appears in breast milk, raising questions about infant exposure that have not been fully resolved.