Aspartame and Cancer: The Sweetener That Never Stopped Being Suspected

This is a history, and the thing that makes it worth telling is that the suspicious part is real. Most food scares run on nothing — a rumour, a forwarded warning, a name that sounds like a chemical. This one grew around an approval process that genuinely was contested, animal studies that genuinely were questioned, and a corporate cast that included a future US Secretary of Defense. If you set out to design a substance that people would never quite trust, you could hardly do better than to have it approved the way aspartame was. The claim that it causes cancer is not supported by the weight of the evidence. But the feeling that something was not right about how it reached the market has a documented spine, and it is the spine of this whole story.

A discovery, and a company with a history

In 1965 a chemist named James Schlatter was working at the pharmaceutical firm G.D. Searle & Company, trying to make a drug for peptic ulcers. He was synthesising a compound and, at some point, got a little of an intermediate on his fingers. Later, licking his finger to pick up a piece of paper, he noticed it tasted intensely sweet. The intermediate was a compound of two amino acids, aspartic acid and phenylalanine — the substance that would be named aspartame. It was roughly two hundred times sweeter than sugar, with almost no calories. For a company, and eventually a food industry, that had spent decades hunting for a sweetener without the metallic aftertaste of saccharin, this was a fortune sitting on a chemist’s fingertip.

Searle now had to prove the compound was safe, which for a food additive meant years of animal testing feeding studies to satisfy the US Food and Drug Administration. The company ran them through the late 1960s and early 1970s, and in 1974 the FDA granted approval for aspartame’s use in dry foods. That looked like the end of the road. It was closer to the beginning.

Almost immediately, objections arrived. A neuroscientist at Washington University in St Louis, John Olney, raised concerns that aspartame — and specifically its aspartic-acid component — might damage the developing brain, drawing on his own research into how certain amino acids acted as “excitotoxins” in young animals. A consumer attorney, James Turner, joined him in formally objecting. The FDA, facing a credible scientific challenge to its own decision, did something regulators rarely do: it put its own approval on hold, staying the 1974 decision before the sweetener ever reached shelves.

The kernel: what the Bressler Report actually found

Here is where the history earns every ounce of the suspicion that followed. As the objections mounted, the FDA turned to look not only at what Searle’s studies had found but at how they had been conducted. In 1975 and 1976 the agency assembled a task force to audit the underlying research on aspartame and several of Searle’s other products. The investigation into the aspartame studies was led by an FDA investigator named Jerome Bressler, and the document it produced in 1977 — the Bressler Report — is the beating heart of the whole affair.

It did not make comfortable reading. Bressler’s team, going through Searle’s raw records, found discrepancies between the animals’ actual fate and what the study paperwork reported. Tissue masses and tumours that had been found in test animals were, in some records, not accurately reflected; animals recorded as having died were later noted as alive; some excised tissues had not been examined as the protocols required. The report catalogued sloppiness, inconsistency, and record-keeping that fell short of what safety science demands. It did not prove that aspartame caused cancer. What it proved was that the studies meant to rule out that possibility had been run in a way that made them hard to trust — and that is a different and more corrosive finding, because it does not settle the question, it poisons the well the answer was supposed to come from.

Around the same period, the affair acquired the detail that would outlive all the technical ones. In 1977, G.D. Searle brought in a new chief executive to turn the troubled company around: Donald Rumsfeld, the former — and future — US Secretary of Defense, then between government postings. Rumsfeld was a Washington figure of considerable weight, and his tenure at Searle coincided with the company’s push to finally get aspartame across the regulatory line. He is not, by any documented account, a chemist who fudged a study; his role was that of a well-connected executive running a company that badly wanted a decision reversed. But for a public trying to make sense of what happened next, the presence of a Washington power-broker at the top of the firm was exactly the kind of detail that turns a regulatory story into a suspicious one.

The fork: approval, and the point the myth leaves the record

What happened next is the hinge of the entire history, and it is worth walking through slowly, because the myth forks off the record at a precise and identifiable point.

Through the late 1970s the aspartame question ground through the FDA’s machinery. A Public Board of Inquiry — three scientists convened to weigh the evidence — reported in 1980 and recommended against approval for the time being, wanting the cancer question resolved before the additive went to market. That should have been a decisive setback. Then, in 1981, a newly appointed FDA Commissioner, Arthur Hull Hayes, reviewed the matter and approved aspartame for use in dry foods, overriding the Board of Inquiry’s recommendation. In 1983 the approval was extended to carbonated soft drinks — the market that would make aspartame a household chemical, poured into diet colas by the billion litres. Hayes left the FDA in 1983 and, not long after, took a consulting position with a public-relations firm that worked for Searle. Nothing about that sequence has ever been shown to be illegal. Everything about it looks, to a suspicious eye, like a revolving door swinging on well-oiled hinges.

Sit with that record for a moment before the myth arrives, because a fair reading has to hold two things at once. A contested additive, audited studies that showed poor record-keeping, a Board of Inquiry that said not yet, a commissioner who said yes anyway, and a subsequent industry job — that is a genuine account of an approval that did not follow the reassuring straight line the public likes to imagine. Someone who came away from the 1980s uneasy about aspartame was reading the situation accurately.

And here is the fork. Uneasy about the approval and aspartame causes cancer in the people drinking it are two different claims, and only the first is supported by the history. The Bressler Report found that Searle’s studies were badly conducted; it did not find, and could not find, that the substance was carcinogenic. A poorly run study that fails to demonstrate safety is not the same as a study that demonstrates harm — it leaves the question open, and an open question is not a guilty verdict. The myth takes the entirely justified mistrust of the process and quietly upgrades it into a specific, physical claim about tumours in human bodies, a claim the process failures never established. The same move recurs across this desk: a real institutional betrayal, precisely because it is real, lends its credibility to a downstream claim it never actually supports. It is the exact machinery that drove the vaccine–autism myth, where legitimate reasons to question medical authority were borrowed by a specific claim the evidence did not carry.

The Nancy Markle email: a hoax with a name

If the 1980s gave the suspicion its foundation, the late 1990s gave it wings, and they were the crudest possible wings. Sometime around 1998 an email began circulating — this was the era when a forwarded message could reach the whole world through a chain of well-meaning aunts — under the byline of a woman calling herself “Nancy Markle.” The message claimed to be the text of a talk given at a health conference, and it asserted that aspartame was responsible for an epidemic of disease: multiple sclerosis, lupus, memory loss, seizures, blindness, and more. It urged readers to throw out their diet drinks and to forward the warning to everyone they knew. Many did.

Almost none of it survived contact with checking. “Nancy Markle” appears to have been a fabrication or a misattribution; portions of the text were lifted from the writings of an anti-aspartame activist and stitched into a viral warning that no medical conference had endorsed. The diseases it named — MS and lupus among them — are not caused by aspartame, and the mechanism the email described was pharmacological nonsense. It was, in the plainest terms, a hoax.

But notice what the hoax did, and why it worked. It did not have to invent the suspicion; it inherited it. By 1998 there was already an atmosphere around aspartame — a sense, seeded by the genuinely messy approval, that this was a chemical the authorities had waved through against resistance. The Markle email dropped into that atmosphere and detonated. People forwarded it because it confirmed something they already half-believed, and the thing they half-believed had a real root. This is how the most durable food myths propagate: the viral lie rides on the back of a legitimate grievance, and the grievance vouches for the lie. The story of how manufactured doubt and real doubt get tangled together is the whole subject of Big Sugar’s decades of manufacturing doubt — and aspartame is a case where the public’s suspicion of one sweet-tasting industry primed it to suspect the next.

The science after the scare: Ramazzini, the cohorts, and Group 2B

The suspicion, having a real root and a viral vector, did not fade — and periodically the actual science threw it fresh fuel. In the mid-2000s the Ramazzini Institute in Italy, led by the researcher Morando Soffritti, published a series of lifetime rat studies (2005 through 2007) reporting increased rates of lymphomas, leukaemias and other tumours in rats fed aspartame, some at doses within the range humans might plausibly consume. Here, at last, seemed to be the physical evidence the myth had always lacked. The headlines were immediate and alarming.

The regulators pushed back, and the reasons they gave matter. The European Food Safety Authority reviewed the Ramazzini data and, in a full re-evaluation of aspartame published in 2013, concluded that the studies had methodological problems — including questions about the rat colony’s background rate of respiratory disease and inflammation, which could produce tumour-like findings unrelated to the sweetener — and that they did not warrant changing aspartame’s safety assessment. One can read that dispute two ways, and honesty requires acknowledging both: either an independent institute found something industry-funded science had missed, or a small set of contested studies failed to replicate the way regulators require before they act. What is not in dispute is that the largest human evidence pointed the other way. In 2006 the US National Cancer Institute published results from a large prospective cohort — around half a million older adults — and found no association between aspartame consumption and lymphoma, leukaemia or brain cancer. Human populations, watched in their hundreds of thousands, did not show the pattern the rats were said to show.

Then came 2023, and the moment that briefly made aspartame front-page news again. In July, the International Agency for Research on Cancer — the World Health Organization’s cancer arm — classified aspartame as “possibly carcinogenic to humans”, its Group 2B. To a headline reader, that sounds like a conviction. It is not, and the distinction is the single most important thing to understand in this whole history. IARC assesses hazard, not risk — it asks whether a substance could conceivably cause cancer under some circumstances, at some dose, not whether it does so at the levels people actually encounter. Group 2B is a large and famously mixed category; it has, at various points, included things like aloe vera extract and pickled vegetables. On the very same day, the WHO’s Joint Expert Committee on Food Additives (JECFA), which assesses risk, reviewed the same evidence and left aspartame’s Acceptable Daily Intake unchanged at 40 milligrams per kilogram of body weight — a figure that works out to a great many cans of diet drink per day for an average adult before the limit is reached. Two WHO bodies, the same evidence, two answers that only sound contradictory: one said we cannot fully rule out a hazard; the other said the actual exposure is within safe bounds. The myth hears the first sentence and never reaches the second.

Why the suspicion never died

So the evidence record, read whole, is undramatic: an additive that the largest human studies do not link to cancer, flagged by one WHO body as a low-confidence possible hazard while another WHO body affirmed its intake limit on the same day. That is not the stuff of a scare. And yet the scare persists, decade after decade, in a way that the science alone cannot explain. To understand why, you have to go back not to the chemistry but to the approval.

Because the approval was, in fact, unreassuring. The public was asked to trust that aspartame was safe on the strength of studies that an FDA audit had found to be badly kept; the reassurance came from a commissioner who overrode his own Board of Inquiry and then went to work adjacent to the company; the firm had been run by a Washington heavyweight during the crucial push. None of that proves harm. All of it corrodes trust — and trust, once corroded, does not care very much what the epidemiology says thirty years later. A person who does not believe the process was honest has no reason to believe the reassurance the process produced. The Markle email understood this instinctively, even if its author understood nothing else: you do not need real evidence of harm if you have real evidence that the gatekeepers cut corners, because the second thing makes people supply the first thing themselves.

There is a deeper pattern underneath, and it is the reason this desk keeps returning to sweeteners and food and the agencies that police them. When an industry has been caught, even once, shaping the science that regulates it — the documented history behind the great sugar cover-up — every subsequent reassurance about anything sweet arrives pre-suspected. The suspicion is not irrational; it is learned, and it was taught by real events. Aspartame walked into a food culture that had already, correctly, learned not to take the industry’s word at face value, and it walked in through a door that swung the wrong way at exactly the wrong moment.

That is the honest end of it. The people who never quite trusted aspartame were not fools frightened by a chain email, though a chain email certainly found them. They were responding, often without knowing the details, to a genuine unease that the record justifies: an approval that looked engineered, studies that had been audited and found wanting, a revolving door that turned at the decisive hour. The specific claim they were handed — that the sweetener gives you cancer — is not what the evidence shows. But the question underneath it, can I trust the people who told me this was safe, given how they told me, is a fair question, and it was made fair by things that actually happened. A myth this stubborn is almost never sustained by ignorance. It is sustained by a memory of the one time the gatekeeper blinked, and by the entirely human refusal to forget it.