Aspartame, an artificial sweetener approximately 200 times sweeter than sugar, has been used in thousands of products worldwide since the 1980s, including diet sodas and sugar-free desserts. Its widespread use is due to its ability to provide sweetness with a negligible caloric contribution. For decades, the safety of aspartame has been a subject of public interest and scientific debate, particularly concerning a potential connection to cancer. Examining the current scientific evidence and the positions of regulatory agencies provides a clearer picture of this discussion.
The Conflicting Classifications
In 2023, the conversation around aspartame was reignited when two expert committees of the World Health Organization (WHO) released assessments with seemingly contradictory conclusions. This divergence stems from the different questions each group is tasked with answering. One group, the International Agency for Research on Cancer (IARC), is a hazard identification body. Its primary role is to determine if a substance can cause cancer under any possible circumstance, not how likely it is to do so in real-world scenarios.
The IARC classified aspartame as “Group 2B,” meaning it is “possibly carcinogenic to humans.” This classification was based on what the agency described as “limited evidence” of a link to liver cancer in some human studies. To provide context, the Group 2B category includes a wide range of substances, such as aloe vera whole leaf extract and traditional Asian pickled vegetables. This classification signifies that while there are some indications of a potential hazard, the evidence is not conclusive.
In contrast, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) performs risk assessments. JECFA’s role is to determine the actual probability of harm occurring under specific conditions and levels of exposure, such as through daily diet. After reviewing the same scientific data as the IARC, JECFA concluded that the evidence of an association between aspartame and cancer in humans was not convincing. JECFA reaffirmed its position that aspartame is safe for consumption within the established Acceptable Daily Intake (ADI) of 0–40 milligrams per kilogram of body weight.
A Deeper Look at the Scientific Evidence
The IARC’s “possibly carcinogenic” classification rests on “limited evidence” from a few observational studies in humans. These studies suggested a potential association between the consumption of artificially sweetened beverages and a type of liver cancer called hepatocellular carcinoma. The term “limited” is a specific IARC designation used when a positive association is observed, but researchers cannot rule out other factors like chance, bias, or confounding variables.
Evidence from studies on experimental animals has also been inconsistent. Some studies on rats suggested a potential link to blood-related cancers, but subsequent reviews by regulatory bodies identified significant shortcomings in the study designs, making the results difficult to interpret. Other animal studies have not found evidence of a carcinogenic effect, creating a mixed and debated body of literature.
Further complicating the argument for a cancer link is aspartame’s metabolism. When consumed, the body rapidly breaks it down in the small intestine into three common components: two amino acids (aspartic acid and phenylalanine) and a small amount of methanol. These substances are handled by normal metabolic processes and are also found in much larger quantities in everyday foods like milk, meat, and vegetables. Because aspartame does not enter the bloodstream intact, many scientists question the biological plausibility of it causing cancer at typical consumption levels.
What Major Food Safety Agencies Say
National regulatory bodies have largely maintained their position on aspartame’s safety. In the United States, the Food and Drug Administration (FDA) has consistently stated that aspartame is safe for the general population, having reviewed extensive scientific evidence since its first approval in the 1980s.
Following the 2023 IARC classification, the FDA issued a statement disagreeing with the conclusion that aspartame is a possible carcinogen. The agency noted its own scientists identified “significant shortcomings” in the studies IARC relied upon. The FDA continues to affirm that scientific evidence supports the safety of aspartame within its Acceptable Daily Intake (ADI) of 50 mg/kg of body weight.
This position is mirrored by other major international regulators. The European Food Safety Authority (EFSA), which conducted a comprehensive risk assessment in 2013, also concluded that aspartame and its breakdown products are safe for human consumption at current exposure levels. EFSA’s experts specifically ruled out the potential for aspartame to cause genetic damage or induce cancer.
Understanding Your Aspartame Consumption
For consumers, the scientific debate often comes down to a practical question: how much is too much? The Acceptable Daily Intake (ADI) set by JECFA is 40 milligrams per kilogram of body weight per day, while the FDA’s is slightly higher at 50 mg/kg. This ADI is a conservative figure, representing the amount that can be ingested daily over a lifetime without an appreciable health risk. To exceed JECFA’s ADI, an adult weighing 70 kilograms (about 154 pounds) would need to consume more than 9 to 14 cans of diet soda every day.
Data on actual consumption shows that the vast majority of people consume amounts far below this threshold. Even individuals who are high consumers of products containing aspartame fall well within the safe limits established by regulatory bodies. This gap between typical consumption and the ADI is a central reason why risk-assessment agencies remain confident in its safety for the general population.
There is one group for whom aspartame poses a known and direct risk. Individuals with the rare genetic disorder phenylketonuria (PKU) cannot properly metabolize phenylalanine, one of the amino acids produced when aspartame is broken down. A buildup of phenylalanine can be toxic to the brain, so people with PKU must follow a strict diet low in this amino acid. For this reason, all products containing aspartame are required by law to carry a warning label indicating the presence of phenylalanine.