Medical Examiner

A Diet Coke Zealot Demands Answers About the Aspartame Cancer News

Bottles of Diet Coke.
Yes you can have these—when you pry them out of my ice-cold, dead hands. Justin Sullivan/Getty Images

Thursday morning, Reuters reported that the International Agency for Research on Cancer—the cancer research department of the World Health Organization—is set to declare aspartame a possible carcinogen in July. Another department, the Joint WHO and Food and Agriculture Organization’s Expert Committee on Food Additives, will issue new findings at the same time. As a documented fanatic of Diet Coke, I felt alarm: Would my view of Diet Coke as a tonic that cures all ills be contradicted? Was Joe Biden going to ban Diet Coke the way he definitely wants to ban gas stoves? Would it be possible to establish a kind of aspartame “safe haven” in international waters? I called an expert on risk, Kevin McConway—emeritus professor of applied statistics at the Open University in England—to talk me down. Our conversation has been edited and condensed for clarity.

Dan Kois: Thank you for speaking with me. Obviously, I am looking for reasons it is still OK for me to drink Diet Coke, because without it I’ll die. Should I panic?

Kevin McConway: It is too early to panic.

So the World Health Organization is not going to break into my kitchen tomorrow and pour all my Diet Coke down the sink?


Well, it wouldn’t be tomorrow! Who knows—when you see what they finally say, you may want to pour it down the sink yourself.

I would never. So there are two WHO groups that are about to issue rulings on aspartame? The IARC and the JECFA?

They have different jobs. The IARC assessments always have been difficult to make sense of. They don’t really quite say what people think they are saying. They make assessments of the hazard of different agents that might cause cancer in humans. What they mean by hazard is: Could it possibly, under any circumstances, increase the chances of cancer in most people? They’re not assessing the actual risk in the real world of drinking Diet Coke. They would never go as far as saying, “It does cause cancer if you drink enough of it.” They just say: “The science says this agent is probably a hazard, or possibly a hazard.”


They’ve also said that working overnight is probably a hazard and using a cellphone is possibly a hazard.

In none of these cases do they say there actually is a risk. It’s not their responsibility to do that. In this case, that responsibility lies with the JECFA. They’re an expert committee on food additives. It’s their job to determine the risk of things like that and make recommendations for what is a safe level of consuming them.

They’ve already made recommendations on aspartame.

Yes, in 1981, I believe.


They said you’d have to drink between 12 and 36 cans of diet soda per day to be at risk.

Of course it’s depending on body weights, with differing amounts for children. It’s still quite a lot!

A lot, sure.


It’s up to JECFA to take the evidence from IARC, and other sources, into account, and what is supposed to happen is that IARC and JECFA are supposed to report their findings on the same day, which is July 14. Reuters has this source saying that the IARC is going to declare that aspartame is possibly a hazard, which is the third level of hazard—below “definitely a hazard” and “probably a hazard.” But we don’t know how the JECFA will respond to that.

So it’s the JECFA recommendation, whatever it is, that might determine policy with different national governments.

Different governments don’t always go exactly where those recommendations go. But it’s quite a strong guide.


Who’s on these committees? Are they primarily people who hate joy and happiness?

As far as I know, no. They are toxicologists. They are statisticians who understand about risk. They’re experts! With the IARC, it’s always been confusing, because though they’re determining hazard, they used to include “risk” in the name. They’ve since changed that. But there is this technical difference between risk and hazard that most people who are not working in risk assessment don’t understand.

I sure don’t.

Think of being hit by a meteorite.



The hazard from meteorites—there’s a possibility of harm under certain circumstances, because if a meteorite hit you, it could kill you! It’s a rock from space. But the risk is extraordinarily low, because there’s only been one person in recorded history who was hit by a meteorite.

Oh, I’ve never thought about it that way.


What people want is for somebody to say, look, it’s risky if you drink 50 cans of Diet Coke a day—

Is it?!

—and it’s not risky if you drink one. These toxicologists are looking at something different. Most people don’t care about, I don’t know, if I consume aspartame in some other way, if I snort it, is it going to cause cancer in me. That’s not a question you ever ask, but it is a question toxicologists might ask.

So what will happen on July 14?

Let’s suppose Reuters is right about what IARC are going to say. They’re going to put aspartame in this possibly-causing-cancer category, along with, oh, putting talcum powder on your privates, or working in a dry cleaner. They’re saying there is some evidence, but they’re not saying the evidence is foolproof, and they’re not saying anything about how risky it is. I have no idea what JECFA will say. They may say, “What we said before is fine.” They could even say the limit could be higher.

That would be great.


Or they may say that you shouldn’t touch this stuff at all. Anything’s possible. That is the time to think about changing a habit—or not changing a habit! Maybe you’ll say, “I still love the stuff, and I will continue to drink it.”

Maybe so. So July 14 is when I’ll need to start thinking about hoarding Diet Coke.


Ideally you would want to look at why they’re changing the recommendations. They won’t just say, “This is the number.” They will give reasons for whatever the recommendation is. And IARC will write a long monograph giving all their evidence, which you probably wouldn’t get through.

I bet if I pounded 50 cans of Diet Coke I could get through it!


Maybe. Good luck to you. I’m not a Diet Coke fan, but if I were, I would not be worrying about this at this stage. It’s just too early to say. When I saw that the two bodies are issuing their results on the same date I thought, that’s good, because maybe people just won’t pay attention to the IARC. Because there’s such a risk of confusion.

A risk of confusion or a hazard of confusion?

There’s certainly a hazard of confusion! But I think there’s a risk as well. I hope the stories about it on that date make things clear.

And then I’ll have to face the music.

Well, you’ve got to drink something! Nothing in life is entirely risk-free. I leave it up to you.