You may have come across headlines after the WHO classified that aspartame (the artificial sweetener in most diet soda) is a “possible carcinogen” and that heavy users should exercise caution:
"Our results do not indicate that occasional consumption should pose a risk to most consumers," said Dr. Francesco Branca, director of the Department of Nutrition and Food Safety at the WHO. He said the problem is for "high consumers" of diet soda or other foods that contain aspartame. "We have, in a sense, raised a flag here."
What does that mean?
What is a possible carcinogen?
Why does the World Health Organization randomly come out with a position on Diet Coke in 2023?
Let’s look into this a bit more.
Classifying something as a possible carcinogen is very different than saying it actually causes cancer
The WHO has a classification system with regards to the level of evidence that any particular substance causes cancer:
In Group 1, the known cancer causing agents, we have things like the following:
Tobacco use and secondhand smoke
Asbestos
Alcohol use
Helicobacter pylori, the bacterium that increases risk of stomach cancer (but reduces risk of esophageal cancer)
Hormone replacement therapy (post menopausal) and birth control (also documented to lower risk of endometrial and ovarian cancers)
Viruses like HIV, hepatitis B, HPV, and hepatitis C
Occupational exposures like working as a firefighter or a painter
You can look at the comprehensive list here.
The WHO carcinogen classification is based on a few different characteristics and it’s actually somewhat arbitrary
The WHO looks at 3 lines of evidence to classify the carcinogenicity of a given substance:
Evidence that a substance causes cancer in experimental animals
Evidence of a plausible biologic mechanism through which the substance causes cancer
Evidence that a substance causes cancer in humans
For aspartame, the evidence on all 3 counts is limited:
Aspartame was classified as Group 2B on the basis of limited evidence for cancer in humans, limited evidence for cancer in experimental animals, and limited mechanistic evidence.
Looking at the publication in a bit more detail reveals there’s even less smoke than I had anticipated based on the headlines.
The signal for cancer risk related to aspartame is incredibly weak.
The studies on humans are unpersuasive, there is no plausible biological mechanism, and the studies suggesting risk with lab animals look at incredibly high doses.
And you have to be careful when extrapolating any study in animals to people - just because something causes cancer in a rat doesn’t mean you can draw any conclusions about the risk in a human.
Even the WHO suggests that aspartame is safe as long as you keep the daily quantity you consume at or under 40mg per kg of body weight.
This means that WHO says that the average person (we’ll say 70kg or 154 pounds) could consume 2800mg of aspartame daily and be totally fine.
For perspective, that is 14 cans of Diet Coke a day, every single day for your life, and you’re fine, say the folks who suggest aspartame is a possible carcinogen.
There is very little reason that this should be reported
The quality of evidence here is so low that I almost didn’t write about it - to be honest, the suggestion that this is anything other than extrapolated guesswork is ridiculous.
It’s interesting to read the quotes from the folks at the WHO - they are measured, hedging, and reassuring - and contrast that with the media headlines suggesting something much more ominous:
Ultimately, if you just read the headline, you’re going to be misled. That’s unfortunately the nature of health news way too often today - the endless need for more content and more clicks hypes up unimportant findings.
And that’s the most important take-home message with this report: the findings are unimportant and should not impact anything that you’ve been doing.
If you’ve been drinking more than 14 Diet Cokes a day, you should probably reduce that amount for reasons that go far beyond reduction in cancer risk.
This gets to a larger issue in medicine - every organization doesn’t need to take a position on every issue at hand
I’m not sure that we need to live in a world where the WHO takes a public position on the need for more research on the safety of compounds that humans ingest regularly in the absence of new compelling research that there’s a problem.
Having a position on everything often means that your important positions get lost.
When the WHO media apparatus puts out something like this, it undercuts the important work that they do.
And make no mistake, the people who put out this report knew how it would be amplified by the media (just like they knew the research is nonsense, which is why all the on-the-record quote were so hedging and equivocal).
The need-to-comment problem extends beyond the WHO to many other organizations in medicine.
We have a real advocacy problem in medicine - there’s a banal uselessness of advocacy when organizations in medicine seem to increasingly feel a need to comment on every societal problem.
I’m not suggesting that we all need to “stay in our lane,” but I am suggesting that medical organizations don’t need an official position on every hot-button political issue.
After the Supreme Court ruled to overturn Roe vs. Wade, there was a push to stop scheduling medical conferences in states that restricted access to abortion.
This newsletter isn’t meant as a commentary on that ruling. But I don’t really get why medical organizations should be responding to a court ruling by penalizing all of the people who live and work in a state regardless of their individual support for the ruling.
Not to mention the fact that when a medical organization takes a political position, there’s an implicit suggestion that that physicians aren’t allowed to have differing positions on important issues.
That’s a slippery slope to go down, regardless of how you feel about this one issue.
Multiple medical societies have started to take positions on climate change, even to the point where the incoming president of the American Society for Preventive Cardiology wrote an editorial to draw unique focus on the topic for preventive cardiologists.
But there’s a big leap from acknowledging that air pollution contributes to cardiovascular disease to suggesting that climate change is an important issue for the American Society of Preventive Cardiology to comment on and that its members need to advocate for (or have unanimous political positions on).
When you don’t prioritize what to advocate for, you end up advocating for nothing.
And so I am a firm believer that physicians and public health organizations should be thoughtful about the public positions that we take and not feel the need to take them on everything.
If you want people to take you seriously, sometimes it’s okay not to have an opinion.