EXPERT Q&A

Years-long debate on a possible link between cancer and aspartame—sweetener of Diet Coke and thousands of other foods—was not settled with the World Health Organization’s decision to classify the artificial sweetener as possibly carcinogenic while also maintaining the current recommendation of safe daily intake.

The decision was based on somewhat conflicting rulings from two WHO committees, the International Agency for Research on Cancer (IARC) and the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

IARC’s 25 international experts evaluated research and found an increased risk of cancers but not enough consistent evidence pointed to moving aspartame to WHO’s highest risk category for carcinogens. Instead, it designated aspartame as possibly carcinogenic, a category that includes an array of products consumed regularly.

JECFA, on the other hand, deemed evidence too inconclusive to change the daily recommended intake of aspartame and said current daily intake of 40 milligrams per kilogram of body weight, or between 9 and 14 cans of diet soft drink per day for someone weighing 150 pounds, was still considered safe. The U.S. Food and Drug Administration chimed in to disagree with the IARC’s carcinogen classification and support JECFA’s daily intake status quo, perhaps raising more questions for consumers and lovers of the 6,000 plus products that contain aspartame.

Jackie Goodrich is a toxicologist and research associate professor of environmental health sciences at U-M’s School of Public Health. She served on the IARC committee that assessed whether working as a firefighter (and the exposures that come with the occupation) causes cancer. Her research explores links between exposures to chemicals and adverse health impacts on children and workers. She also investigates how chemicals cause harm in the body.

What should consumers take away from the IARC’s decision to designate aspartame a carcinogen?

Consumers should be aware that this designation means the evidence across different types of studies is not enough to link aspartame to cancer with confidence. There has been evidence in certain studies linking aspartame to cancer, but there is inconsistency when looking across all studies. There are also limitations that do not allow scientists to directly link aspartame to cancer. Other things that we call confounders might explain the link, and scientists have work to do to figure out the true cause and effect relationship. In the meantime, we already know that consuming high amounts of sugar is not good for health. Thus, consumers should take a metered approach and find ways to reduce their overall consumption of sugar and artificial sweeteners without necessarily cutting one particular sweetener fully out of their diets.

What is aspartame made of?

Aspartame is not naturally occurring and has to be manufactured. It is made of a modified version of phenylalanine and aspartic acid linked together; these are both amino acids that form the building blocks for proteins in humans and other animals.

Why has talk of health risks linked to artificial sweeteners lingered so many years with no definitive findings?

Over the years, fairly convincing studies in both rats and humans have linked aspartame or artificial sweeteners in general to several cancers. These studies raise concern about aspartame and, in some cases, other sweeteners. However, the evidence has been inconsistent with other studies showing no association with cancer.

The process by IARC systematically reviews all evidence, weighted by the strengths and limitations of each study design, instead of being driven by one study alone.

Would you drink or eat aspartame?

As a toxicologist, I recognize that reducing harmful (or potentially harmful) exposures whenever I can is beneficial. As a public health professional, I also know that heavy consumption of sugar sweetened beverages is not a healthy choice. I limit my consumption of both sugar sweetened and artificially sweetened beverages and products like yogurt but do not avoid them completely. Whenever I can, I seek out alternatives like naturally low sugar yogurt, unsweetened teas, etc. I also consume products with natural sweeteners like Stevia, but try to avoid becoming dependent on one particular sweetener. As science advances, sometimes we find evidence we do not expect about our favorite products.