The World Health Organization Says Aspartame is Fine, Actually

The World Health Organization has said three different things about aspartame this year. First, they said not to use sweeteners like aspartame for weight loss. Next, they designated aspartame, the sweetener in Diet Coke, a “possible” carcinogen. Now, the branch responsible for deciding which food additives are safe has confirmed that aspartame is safe to use in foods. This isn’t actually a contradiction, but to most of us, it probably seems like whiplash and “scientists changing their minds.” Let me explain what it all really means.

The three different announcements, boiled down to plain English, actually say the following, which are all compatible:

If you’re keeping track on a scoreboard, that’s two votes for “aspartame bad” and one for “aspartame good.” But life is not a scoreboard, and science is not won by counting points from either side. Positive and negative things can coexist and all be true.

What is the evidence that aspartame may cause cancer?

As we discussed before, aspartame is in the “possible carcinogen” category, which means we don’t know whether it’s a carcinogen. Now that the official report is out, we can see how IARC, the International Agency for Research on Cancer (which is part of the WHO), summarized the evidence for a link between aspartame and cancer. Spoiler: It is not strong evidence at all. (Bold and italics theirs.)

Limited evidence for cancer in humans, based on findings for liver cancer (specifically, hepatocellular carcinoma). Among the available cancer studies in humans, there were only three studies on the consumption of artificially sweetened beverages that allowed an assessment of the association between aspartame and liver cancer. The three studies (which included four large cohorts) were conducted within the European Prospective Investigation of Cancer and Nutrition (EPIC) cohort, 2 a pooled analysis of the National Institutes of Health (NIH)-American Association of Retired Persons (AARP) cohort and the Prostate, Lung, Colorectal and Ovarian Cancer Screening (PLCO) cohort, 3 and the Cancer Prevention Study (CPS)-II cohort. 4 In these studies, consumption of artificially sweetened beverages was considered a proxy for aspartame exposure, as supported by evidence on the country and time period of aspartame use in beverages. In all three studies, a positive association was observed between consumption of artificially sweetened beverages and risk of liver cancer, either overall or in important subgroups of the studied populations, but bias or confounding could not be ruled out as an explanation for the positive findings.

There was also limited evidence for cancer in experimental animals. There was an increased incidence of malignant neoplasms or a combination of benign and malignant neoplasms in two species (mouse and rat) of animals of both sexes seen in three published studies. However, based on concerns over the study design, the working group concluded that the evidence for cancer in experimental animals was limited. Specifically, in the analyses in the two prenatal exposure studies, no adjustments were made for litter effects (e.g., number of litters, pups per treatment group, etc.), which could lead to false positive results if pups from the same litter responded in the same way to treatment because of genetic factors. Concerns were also expressed regarding diagnoses of lymphomas (predominantly, but not exclusively, those located in the lung). Also, there were unresolved questions on the interpretation of the histology of hepatocellular proliferations and bronchioloalveolar lesions.

In other words, this is not anything as simple as “we gave aspartame to rats and they got cancer.” In the animal studies, experts who looked at the data are still not even sure if the lab rats got more cancer when they were given aspartame. And in the human studies, there was a slightly higher rate of cancer in people who drank a lot of diet soda than people who didn’t, but there are all kinds of reasons why that might be the case (different diet overall, for example) that can’t be ruled out.

You can read the full document with the findings here, if you’d like to dig in further. As for what to do with this information, that ball gets passed to another group within the WHO, the Joint Expert Committee on Food Additives, or JEFCA.

Why did the WHO decide aspartame is safe?

The WHO’s recent announcement is about what they call aspartame’s “hazard and risk assessments.” Those are two different things. Something is a health hazard if we know it has some kind of negative effect on health. Aspartame was judged to possibly be a health hazard.

Risk, on the other hand, is what matters in the real world. What is the risk to us from consuming aspartame? If there is one, it’s low.

The WHO writes in their announcement that JEFCA, their committee on food additives, “considered the evidence on cancer risk, in animal and human studies, and concluded that the evidence of an association between aspartame consumption and cancer in humans is not convincing.”

The committee also writes that when we consume aspartame, it fully breaks down in our digestive system “into metabolites that are identical to those absorbed after consumption of common foods, and that no aspartame enters the systemic circulation as such.” No matter how much Diet Coke you drink, there is no aspartame in your bloodstream.

With those conclusions in mind, the committee decided not to change their previous guideline about aspartame. The “acceptable daily intake” of aspartame is 0 to 40 milligrams per kilogram of a person’s body weight.

How much aspartame is too much?

According to this guideline, 40 mg/kg would be the most you should consume on a daily basis. (To be clear, it’s not like something terrible would happen at 41. This is just the number they have picked to be safe.)

A 12-ounce can of Diet Coke contains 184 milligrams of aspartame, according to a few papers I found, like this one; some estimates of sodas in general put the typical number at 200 to 300 milligrams.

Next, we need to consider this in relation to our own body weight. (It’s pretty typical for doses of medicines or toxins to be calculated in terms of body weight, since it usually takes more of a substance to have an effect on a bigger person than a smaller one.) A kilogram is 2.2 pounds. If you weigh 220 pounds, that’s 100 kilograms.

So, let’s do the math. Me, I weigh about 70 kilograms. I also drink my Diet Cokes in 16.9-ounce bottles. Each of those bottles amounts to a dose of 3.7 milligrams per kilogram, for me. That means I could drink ten of my Diet Cokes a day, every day, and still be within the range that WHO says is acceptable. (That’s more than a gallon. That’s more than twice the amount of liquid you’d consume if you had eight glasses of water a day. I don’t think anybody my size is in danger of accidentally consuming ten 16.9-ounce bottles of anything.)

Aspartame is in more than Diet Coke, of course, but it’s also just one of many artificial sweeteners that exist. Many drinks, yogurts, protein bars, and other products use other sweeteners than aspartame. They might use acesulfame potassium (“ace-K”), sucralose, or “natural” non-sugar sweeteners like stevia or monkfruit. Then there are the sugar alcohols, like erythritol. Personally, I avoid most of these, but not for any health reason—I just think the aftertaste is kind of gross, and I’d rather have the full-sugar versions of these products if I’m going to eat them at all. But we all have our questionable tastes, and I’ll have to agree with my colleague Claire Lower that it would be nice if we could just drink our damn Diet Cokes in peace.