You don’t have to freak out about aspartame in your diet soda

Yesterday, Reuters broke the news that the World Health Organization’s International Agency for Research on Cancer (IARC) will declare aspartame as “possibly carcinogenic” next month. However, that doesn’t mean you have to raid your pantry and toss any sugar-free foods containing the artificial sweetener.

Why? Because this is not the agency that consumers should listen to with regard to food safety. The IARC only assesses the hazard of a given substance, not the risk. For example, there is a hazard of a meteor destroying the Earth or the sun causing skin cancer. But that’s not what matters to the average person. What matters is the actual risk of a hazard happening. There are thousands of meteors in space, but only the ones hurtling toward Earth pose a risk. The sun’s rays are dangerous, but you reduce that risk by using sunscreen, wearing protective clothing, and avoiding tanning beds.

The IARC reviews data about a substance and then declares whether it’s carcinogenic, probably carcinogenic, possibly carcinogenic, or unclassifiable. Technically speaking, that means any substance it reviews can’t be ruled out as non-carcinogenic. That’s why IARC can list things like “very hot beverages,” aloe vera, and wood dust as potential causes of cancer, even though your actual risk of developing cancer from these items is low.

So who does assess risk, and who should you look to for guidance with regard to food safety? Within the WHO, that task falls to the Joint FAO/WHO Expert Committee on Food Additives (JECFA). In the US, it’s also the purview of the Food and Drug Administration. JECFA has ruled aspartame safe for consumption since 1981, while the FDA has also deemed that aspartame is safe for the general population. On its site, the FDA says it’s reviewed over 100 studies on aspartame and that the agency reevaluates the safety of aspartame anytime there are objections raised to aspartame’s approved uses.

So why is there a renewed hullabaloo around aspartame? One issue is the fact that both IARC and JECFA are currently reviewing aspartame and are set to publish their reports on July 14th. The timing was also flagged by food safety agencies, including the FDA, as potentially confusing to consumers.

“In our opinion, a concurrent review of aspartame by both IARC and JECFA would be detrimental to the scientific advice process and should not occur,” the FDA wrote in a letter to the WHO last summer. “We believe that JECFA is better suited to assess any risk associated with the consumption of aspartame and should be WHO’s lead entity in assessing and providing public health recommendations about the safety of aspartame in food.”

The letter goes on to explain that the agency views JECFA’s review process to be more reliable than IARC’s as the latter only reviews public data. JECFA reviews all available data, public or otherwise. It also points out that JECFA’s review of aspartame was proposed in 2021 and endorsed by 188 countries.

“JECFA, the FDA, the European Food Safety Authority, they’re doing reviews of a lot of evidence for aspartame,” Daniele Wikoff, PhD, principal scientist and health sciences practice director at ToxStrategies, tells The Verge. Wikoff also notes that there’s a large body of high-quality scientific research that says aspartame is safe for human consumption. “These agencies have evaluated, re-evaluated, and reaffirmed the safety of aspartame repeatedly over the past 40 years. This includes evaluating new science as it becomes available.”

Wikoff explained that JECFA also evaluates food safety from multiple angles, not just cancer, meaning JECFA’s report would be more representative of the totality of aspartame’s health risks.

Food safety agencies, like JECFA and the FDA, are also the ones responsible for defining the accepted daily intake (ADI) of any particular food additive.

“ADI just by definition, is the amount that you can have every day over the course of a lifetime without effects,” says Wikoff, adding that scientists include a “safety factor” — a buffer, so to speak — when determining ADI. “The way that it’s set is not the level where you see effects, it’s well below to ensure levels are health-protective.”

The FDA sets the ADI for aspartame at 50mg per kilogram of weight, while JECFA has it at 40mg. So say you weighed 150 pounds. By that measure, you could have roughly 3,400mg per day. A packet of NutraSweet, which contains aspartame, is about 37mg. A 12oz can of Diet Coke has around 200mg. That means you could consume around 91 packets of NutraSweet or 17 cans of Diet Coke every day for the rest of your life. It’s common sense not to do that, but it’s illustrative that toxicity lies in the dose.

Of course, everybody reacts differently to certain substances. If you’re prone to headaches, you might want to avoid aspartame, as some studies indicate the sweetener may trigger headaches and migraines for some people. Similarly, the American Cancer Society points out that carcinogens don’t always cause cancer in every circumstance. Some require constant exposure over a lifetime; others are more likely to cause cancer if you have certain genetic factors. Medications can also be classified as carcinogens for one type of cancer but be an effective treatment for a different type of cancer.

The bottom line is a leaked report from a non-food safety agency is not what you should base your decision to consume aspartame on. It’s one of the most studied sweeteners, and it undergoes periodic, rigorous review by food safety agencies. Until those agencies say otherwise, there’s no need to panic.