Current research does not suggest that drinking Diet Coke or other beverages with aspartame will increase the risk of cancer.

Aspartame, an artificial sweetener, is found in foods and drinks like Diet Coke. It’s been in the news in recent years, as people have been concerned it could cause cancer. But the evidence for this is weak.

Besides, the average person’s consumption of aspartame has not been linked to cancer. A can of diet soda contains only a tiny amount of the sweetener — way below the acceptable daily intake.

In 2023, the International Agency for Research on Cancer (IARC) declared that aspartame was possibly carcinogenic to humans, meaning it may have the potential to cause cancer.

This led many to worry as aspartame is found in lots of things that we eat and drink regularly.

IARC finding and classification

The IARC classified aspartame in group 2B, the third highest of four ratings.

It said that there was “limited” evidence for it causing cancer in humans (specifically, a type of liver cancer) as well as “limited” evidence for it causing cancer in laboratory animals.

The IARC ratings are as follows:

  • Group 1: carcinogenic to humans
  • Group 2A: probably carcinogenic to humans
  • Group 2B: possibly carcinogenic to humans
  • Group 3: not classifiable as to carcinogenicity to humans
  • Group 4: probably not carcinogenic to humans

FDA response to IARC classification

The Food and Drug Administration (FDA) disagreed with the IARC’s findings, stating that the studies referenced had “significant shortcomings.”

“Aspartame is one of the most studied food additives in the human food supply,” the FDA stated.

“To determine the safety of aspartame, the FDA has reviewed more than 100 studies designed to identify possible toxic effects, including studies that assess effects on the reproductive and nervous systems, carcinogenicity, and metabolism.”

The FDA has no safety concerns regarding aspartame being consumed at safe levels.

JECFA report

The Joint FAO/WHO Expert Committee on Food Additives (JECFA) is another body that assesses the safety of food additives.

In 2023, after the IARC classification, it found no convincing association between aspartame and cancer in people and did not change its recommended acceptable daily intake.

JECFA also noted that aspartame is broken down into substances similar to those produced by other foods.

Additionally, there’s no known way oral exposure to aspartame leads to cancer.

A small number of studies have proposed a potential risk of cancer with aspartame consumption. One published in 2016 noted an association with liver cancer.

However, further studies have found no association.

These include large-scale studies. In 2012, a study involving more than 100,000 people found no strong link between diet soda and cancers like leukemia, non-Hodgkin’s lymphoma, and myeloma.

While there were potential detrimental effects of diet soda, the study’s authors said these could be due to chance.

Research published in 2023 found no association between artificial sweetener consumption and cancer.

Similarly, another 2023 review that examined many studies on the topic found no associations in most published research.

The authors noted that some increased risks for bladder and pancreatic cancers found in certain studies were not backed up by further research.

Their conclusion? There’s no evidence of a risk of cancer with artificial sweeteners like aspartame.

The FDA, which regulates artificial sweeteners, has set an acceptable daily intake of 50 milligrams (mg) per kilogram (kg) (2.2 lb) of body weight.

JECFA and the European Food Safety Authority (EFSA) set their recommended daily intake a little lower at 40 mg per kg of body weight.

That means that an adult weighing 70 kg (154.3 lb) would have to drink more than 9 to 14 cans of diet soda daily to exceed the recommended JECFA or EFSA intake.

For the average person not exceeding the acceptable daily intake, aspartame is not known to pose any serious risks or have any major side effects.

Research has found consuming sweeteners (which may contain aspartame) may put people at greater risk of the following:

  • weight gain
  • diabetes
  • heart disease
  • stroke

There’s also limited evidence of a risk of preterm delivery with aspartame. However, this hasn’t been supported by other studies.

The only confirmed risk is for people with the genetic condition of phenylketonuria (PKU). Their bodies cannot break down an amino acid found in aspartame called phenylalanine.

If this builds up inside the body, it can lead to brain damage. So, people with PKU should steer clear of anything containing aspartame.

The same applies to people with advanced liver disease or those who are pregnant and have had high levels of phenylalanine detected in their blood.

Right now, there is no strong evidence to suggest aspartame can cause cancer or any other serious issues for the average person. The only concern is for people who can’t break down the amino acid phenylalanine inside their bodies.

According to organizations like the FDA and JECFA, consuming up to 40 or 50 mg per kg of body weight daily is safe. As a can of diet soda contains only a small amount of aspartame, most people are unlikely to consume more than the recommended daily intake.

Lauren Sharkey is a U.K.-based journalist and author specializing in women’s issues. When she isn’t trying to discover a way to banish migraines, she can be found uncovering the answers to your lurking health questions. She has also written a book profiling young female activists across the globe and is currently building a community of such resisters. Catch her on Twitter.