The World Health Organization (WHO) International Agency for Research on Cancer (IARC) recently published the first ever monograph on aspartame, classifying it as possibly carcinogenic to humans (group 2B) based on “limited evidence for cancer in humans, limited evidence for cancer in experimental animals, and limited mechanistic evidence.”

This classification does not apply to cancer in general, but is specific for a single type of liver cancer known as hepatocellular carcinoma. Moreover, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) concluded that there was no sufficient reason to change the previously established acceptable daily intake limit of 40 milligrams per kilogram of body weight.

The IARC’s evidence for a link between aspartame and liver cancer comes from three studies that examined the consumption of artificially sweetened beverages. These studies included 477,000 adults across 10 European countries, 553,000 adults with diabetes in the US, and 934,000 adults in the US. In all cases, artificially sweetened soft drinks were used as a proxy for aspartame consumption — actual aspartame intake was never directly measured.

Another important study used in the IARC assessment was the NutriNet-Santé cohort study (2022). This study followed over 100,000 French adults for an average of 8 years, and reported that aspartame consumption was associated with a higher risk of developing any cancer, breast cancer (highest consumers only), and obesity-related cancers (highest consumers only).

Mechanistically, aspartame is readily metabolized into three molecules after consumption: phenylalanine, aspartic acid, and methanol. It’s methanol that is implicated in liver cancer, since it is further metabolized into the DNA-damaging formic acid. However, the amount of methanol and formic acid produced is incredibly small (you get about six times more from a cup of apple juice than a cup of aspartame-sweetened soft drink).

Based on the available data, there is no reason to fear modest consumption of aspartame.