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Aspartame, the artificial sweetener in most diet sodas, has been blamed for diseases and health problems like multiple sclerosis, cancer, and birth defects. But a deep dive into the controversy reveals a reputation marred by inept scientists and panic based on hearsay.
It’s a widely held belief that aspartame, the main artificial sweetener in most diet sodas (branded Nutrasweet® and Equal®), is dangerous. It’s nearly a household fact.
But if you ask a handful of friends why aspartame is bad for you, they all might offer a different answer. Aspartame has been associated with a range of diseases and conditions, including:
...Oh! You thought I was finished? HA! Don’t forget…
...birth defects and death.  
For just one article out of the series on artificial sweeteners, we’re going to take a look at the history of sweeteners.
When it comes to aspartame, the story is too good to overlook. It has everything: crooked scientists, falsified research, an actual conspiracy, and experts that don’t exist.
But if you don’t have time to go down the rabbit hole with me on this one, I’ll answer your question up front: currently, there is no compelling reason to think the common artificial sweetener, aspartame, is harmful in reasonable doses.
According to the American Chemical Society (an independent organization of chemists that publishes about 50 academic journals), if you wanted to ingest a dangerous level of aspartame “you’d have to consume 97 aspartame sugar packets or more than 17 cans of diet soda in less than 24 hours.” 
Large doses of 50 and 40 mg/kg bw/day of aspartame is considered safe by the following government agencies and leading experts:
Despite the staggering body of research on aspartame (which the FDA describes as “exhaustive,” which is a nice example of a homonym), as well as the many regulatory bodies ruling aspartame safe, we are still questioning its safety.
Why won’t this issue die? Probably because a quick Google search might convince you that aspartame belongs on a long list called “Crap that shouldn’t be in soda,” right next to cocaine. 
Seizures? Weight gain? ADHD? CANCER?!?
A careful examination of the controversy doesn’t reveal a cancerous additive poisoning a nation.
But it does explain why we're still talking about it today. Between internet hoaxes, misleading research, and possible conflicts of interest, it’s easy to see why people buy into the conspiracy.
1879-1969: Cyclamate, a different artificial sweetener, hits the market and is soon linked to cancer
In 1879, researchers at Johns Hopkins University discovered saccharin, an artificial sweetener 300 times sweeter than sugar.
By 1907, saccharine was used in canned goods. Despite a 5 year period while saccharine was banned as an additive, it largely flew under the radar for the next 43 years.
But saccharin’s reign dissipated when cyclamate, another artificial sweetener commonly known as Sweet ‘n Low, was approved by the FDA, in 1950.
But in 1969, the FDA banned cyclamate when testing found it caused bladder tumors in lab rats. Just 8 years later, a Canadian study then linked saccharin to bladder cancer in rats. Saccharin and cyclamate are both considered safe today. 
Despite the FDA’s recommendation to ban saccharin, Congress overruled restrictions. Saccharin again monopolized the market.
And if you’re wondering why I’m talking about saccharin, it’s because it set the tone for aspartame: the 70s were already skeptical of artificial sweeteners and the government’s ability to regulate them. 
Aspartame was discovered when a researcher inexplicably decided to taste a chemical compound he was studying in his lab, later recalling “I licked my ﬁnger and it tasted good.”
Yikes. Sometimes stupidity leads to discovery.
James Schlatter was actually working on an anti-ulcer drug. On discovering aspartame, his boss, G.D. Searle, agreed to manufacture aspartame.
Remember the name Searle, because if there is a villain here, it’s definitely him. He’s probably the no. 1 reason aspartame still has a bad reputation.
In 1974, Searle submitted 150 studies on aspartame to the FDA. Based on those studies, the FDA concluded that 1.3-1.7 grams a day was considered safe. 
Now, it’s about to get weird.
Before aspartame hit the market, the integrity of the studies offered to the FDA came into question.
In response, an FDA task force and a panel of academic pathologists reviewed some of Searle’s studies. It turns out that Searle is a terrible scientist and a really untrustworthy dude.
They found that the results of a 52-Week Toxicity Study in the Infant Monkey were falsely deemed conclusive.
The study was supposed to perform cognitive tests on monkeys that ingested aspartame for 365 days and then were returned to their normal diet. After, their brain tissue was supposed to be examined for any changes.
The study lacked a control group, the sample was small (only 7 monkeys studies), one monkey died after 300 days, two monkeys ceased receiving aspartame after 200 days, and only one tissue sample was examined. 
The results of this sloppy, poorly designed study could hardly be called conclusive.
A second study that was intended to be a 104 -week toxicity study on aspartame in hamsters was terminated after only 46 weeks.
At 26 weeks,30% of control and aspartame group hamsters were dead. At that time technicians were supposed to gather blood tests from the hamsters.
Aside from the dead hamsters, there was also an issue with the technician’s methodology. Something was wrong with the tests. By the time Searle realized that there was an issue, they were 38 weeks into the study.
So he simply took glucose levels from a substitute group of hamsters and reported their levels for the 26-week levels. 
After examining these studies, among others, the task force concluded that more research was necessary.
The head of that task force, Adrian Gross, even scolded the FDA, claiming, “At the heart of FDA’s regulatory process is its ability to rely upon the basic safety data submitted...our investigation clearly demonstrates that...we have no basis for such reliance now.” 
But how much did we actually learn from this ruling? Certainly, it’s clear that Searle was either terrible at his job or morally compromised (maybe both?). He was likely rushing results so he could push aspartame through FDA approval and in the process, allegedly falsified results. He also had a real disregard for the lives of his test subjects. Simply put, the panel proved that Searle was a real crook. But they didn’t learn that aspartame was dangerous.
Not only was Searle’s methodology suspect, but so was his team.
United States Federal Attorney Samuel Skinner was charged with the investigation of Searle’s studies.
Yet Skinner left his position in the middle of his investigation to join a law firm that incidentally, also represented Searle. The investigation was stalled and the trial was eventually thrown out. 
In 1977, Donald Rumsfeld became the CEO of G.D. Searle & Co. In 1981, he appointed Dr. Arthur Hull Hayes Jr. as the new FDA commissioner. Just weeks later, they submitted a reevaluation of aspartame and Hayes approved the substance for human consumption. 
In part because of the actions of Searle, Rumsfeld, Skinner, and Hayes, in 1987 the US Government Accountability Office (GAO) reviewed the FDA’s ruling on aspartame.
They found that despite the ridiculous circumstances, the FDA followed protocol correctly. Because they have no medical expertise, they made no claim as to aspartame’s safety. 
However, the CDC did. After reviewing 517 complaints about aspartame, the CDC “identified no specific constellation of symptoms clearly related to aspartame consumption…
Despite great variety overall, the majority of frequently reported symptoms were mild and are symptoms that are common in the general populace.
While some reports are undoubtedly due to the coincidence of symptoms and aspartame consumption, and others may be due to the suggestibility of some persons, still others may be attributable to some as yet undefined sensitivity of some individuals to aspartame in commonly consumed amounts.
The only way these possibilities can be thoroughly evaluated would be through focused clinical studies.” 
The CDC review suggested that although there were complaints about aspartame, the complaints were either so varied or commonplace that it was impossible for them to link aspartame with any symptoms, suggesting that more research be conducted.
In 1996, a study published in The Journal of Neuropathology and Experimental Neurology renewed public fear.
The researchers showed a dubious relationship between an increase in brain cancer and aspartame consumption by showing a graph of rates increasing from 1975 to 1992.
As you can see, this graph shows that rates of brain tumors increased from 1975 to 1992. It doesn’t really show much else.
Indeed, it would be quite the turn of events if a product not yet on the market increased brain cancer (aspartame wasn’t approved for consumption until 1981). 
Truly, the amount of possible correlations with the uptick in tumor rates is infinite, including longer life spans, more accuracy, and greater levels of reporting. Olney should have linked brain cancer to ABBA and roller skates, since those were popular in the 70s, too.
And then...just when you thought it couldn’t be any more absurd...Nancy Markle hit the internet.
This isn’t a study, but it does explain why aspartame has been linked to nearly every single ailment known to man.
Ah, the 90s. It’s hard to remember back to a time when we were all so gullible. But that time did exist. And if you were using a computer in 1999, you might have seen this letter, from Nancy Markle:
Markle, who claims to have been at the World Environmental Conference on ASPARTAME, continues to reveal what she learned about “aspartame disease.”
In the two page text, Markle links aspartame to systemic lupus, methanol toxicity, fibromyalgia, spasms, shooting pains, numbness in your legs, cramps, vertigo, dizziness, headaches, tinnitus, joint pain, depression, anxiety attacks, slurred speech, blurred vision, memory loss, blindness, Parkinson’s Disease, birth defects, weight gain, neurological problems, seizures, and of course, death. 
Markle even offers up this unpleasant imagery:
“When [my patients are] off aspartame, their average weight loss was 19 pounds per person. The formaldehyde stores in the fat cells, particularly in the hips and thighs.” 
People were freaked out. “You mean to tell me my thighs are filled with formaldehyde fat pockets!?!?!?!?!?!?”
It seems like the only thing Markle didn’tblame aspartame for was hair loss.
Although, she did claim that “‘The ingredients stimulate the neurons of the brain to death.’” 
Hold up, here’s the deal: The World Environmental Conference on Aspartame never took place and Nancy Markle didn’t exist. But that wasn’t something the unsavvy internet users of the 90s were prepared for.
Soon after, over 6,000 articles (that was a lot of websites in the 90s) popped up referencing lupus and the fictitious conference. 
And because of the absurd amount of symptoms of “aspartame disease,” everyonewas convinced they had been poisoned.
The aspartame controversy is difficult to make sense of in part because the audience has to separate the research and the chemical from the goons that profited from it.
Searle likely falsified evidence. Skinner’s departure surely impacted the investigation. Rumsfeld may have used his political clout to hire Haynes. And Haynes may have been motivated to approve aspartame because of a quid pro quo for his position.
Despite how that information reflects on aspartame, what it can’t reveal is whether aspartame is actually safe. No amount of bad behavior is going to change the way aspartame interacts chemically.
So, conspiracy theories and goons set aside, what does the research actually say?
Aspartame is linked to cancer in rodents, but most scientists don’t consider it a human carcinogen.
In 2006, Morando Soffritti and colleagues at the Cesare Maltoni Cancer Research Center in Bologna, Italy, released a study comparing the long term effects of aspartame ingestion in rats.
They concluded that aspartame might cause cancer in rats in doses that were “very near those to which humans can be exposed.”
In 2010, Soffritti released a second rat study, claiming that the results “confirm that [aspartame] is a carcinogenic agent” in rodents.  
Soffritti’s 2005 study fed groups of 100-150 male and female rats aspartame from 8 weeks until death.
The rats received concentrations of 100,000; 50,000; 10,000; 2,000; 400; 80; and 0 ppm to simulate assumed daily intake by humans of 5,000; 2,500; 500; 100; 20; 4; and 0 mg/kg of body weight. After their natural deaths, a necropsy and examination was completed. 
Soffritti and the team concluded that aspartame “is a multi-potential carcinogenic compound” at doses that are below the safe upper limits of 40 and 50 mg/kg body weight in humans (the equivalent of about 10 cans of diet soda a day). The study found:
Soffritti concludes that aspartame could be a carcinogen at levels around 20 mg/kg body weight in humans, and calls for an “urgent reexamination of the present guidelines on the use and consumption of aspartame.” 
Soffritti’s 2010 study evaluated six groups of 62-122 male and female Swiss mice.
They were fed aspartame in doses of 32,000, 16,000, 8,000, 2,000, or 0 ppm from prenatal life (12 days of gestation) until death.
Like the 2006 study, at death the mice underwent complete necropsy.
Researchers concluded aspartame induces cancer in the livers and lungs of male Swiss mice. 
Despite the impressive scale, the Soffritti studies received widespread critique. Perhaps unsurprisingly, that critique included reviews funded by aspartame manufacturers and affiliated agencies.
But the loudest critics seemed to come from the European Food Safety Authority (EFSA).
In 2011 evaluation on the 2010 Soffritti study, the EFSA concluded that there was a “lack of relevance for human risk assessment of the type of tumors observed in Swiss mice” and that “on the basis of the information available in the publication, the validity of the study...cannot be assessed.”
In a following 2013 report, described as “the most comprehensive risk assessments of aspartame ever undertaken” the EFSA reaffirmed their position on aspartame.   
So, why did this governmental regulation agency disregard the Soffritti studies?
According to the EFSA, Swiss mice have a higher incidence rate in hepatic and pulmonary tumors than what was reported by Soffritti et al.
The EFSA also pointed out that liver and lung tumors in mice are generally not considered relevant for human risk assessment. 
Proponents of both studies argue that the research deserved more weight than other studies because it allowed the rats to live out their lifespan. They argue that studies that autopsy rats at two years don’t allow enough time for cancer to grow.
But the EFSA claims that “older animals are more susceptible to illness...which includes spontaneous tumors.”
They also state that “these attributes can differ between treated and control animals; thus, it is very difficult to causally link tumors in treated animals to treatment or some intervening factor.” 
John Bucher, deputy director of the environmental toxicology program at the US National Institute of Environmental Health Sciences, notes that the statistical analysis is "problematic" because it's tough to compare animals that have died at different ages. 
After ingestion, aspartame breaks down into two amino acids, phenylalanine and aspartic acid, as well as methanol.
Soffritti hypothesized that the metabolite of aspartame, methanol, might have played a role in the development of tumors. 
Proponents of aspartame argue that because methanol occurs naturally in fruit juices and alcoholic beverages in higher amounts than aspartame, consumers shouldn’t worry about extra methanol consumption. 
Despite theoretical concerns regarding the breakdown of aspartame, the majority of the scientific community seems to agree that aspartame is safe at recommended doses.
One 2004 review in the Annals of Oncology stated that with respect to the current literature, there is no reason to be concerned. Researchers concluded,
“Despite some rather unscientific assumptions, there is no evidence that aspartame is carcinogenic...according to the current literature, the possible risk of artificial sweeteners to induce cancer seems to be negligible.” 
In 2006, NCI examined human data from the NIH-AARP Diet and Health Study of over half a million participants.
Increasing consumption of aspartame-containing beverages was not associated with the development of lymphoma, leukemia, or brain cancer. 
A 2008 review by the University of Maryland concluded that “Soffritti et al. (2007) failed to provide convincing evidence of aspartame carcinogenicity.” However, these authors received payment from a producer of aspartame. 
In 2010, an independent double-blind randomized cross over study compared 48 individuals who self-reported to sensitivity to aspartame with 48 non-sensitive participants.
Each group randomly ingested food with 100mg aspartame. Researchers concluded that “there was no evidence of any acute adverse responses to aspartame.” 
The National Toxicology Program (NTP) performed a 2013 review of epidemiologic evidence. The NTP also found no consistent association between the use of aspartame and cancer. 
It’s easy to see why some people are nervous about aspartame.
Its controversial history paired with its popularity has left it scrutinized since the 1970s. And it hasn’t become any less popular.
In 2010, one-fifth of all Americans drank a diet soda on any given day. 
Not only does aspartame’s early history fuel conspiracy theories, but the fact that many of the proponents of aspartame are affiliated with NutraSweet.
Many studies that refute aspartame’s link to cancer are funded by or affiliated with NutraSweet. And while that may be disconcerting, it’s important to clarify that just because a study is funded by a company doesn’t necessarily discredit the findings.
It’s logical--even responsible--that a company that sells a product would be at the forefront of research on that product. However, researchers have noted a trend between funding source and conclusion. 
And it seems like NutraSweet can’t help itself.
Intentionally deceiving websites affiliated by artificial sweeteners appear as independent health sites.
For example, the Calorie Control Council (often referred to as the CCC to make it sound like a government agency) is a trade group for Manufacturers of Artificial Sweeteners. According to its website, the Calorie Control Council represents manufacturers and suppliers of low and reduced-calorie foods and beverages.
One has to wonder, would aspartame be this contested if NurtaSweet reallocated their marketing dollars into independent, peer-reviewed research?
But perhaps the reason why aspartame lacks independent testing is that researchers aren’t very interested in evaluating something that has been researched since the 70s.
The majority of the scientific body trusts and agrees with the various organizations that have evaluated aspartame. This isn’t an exhaustive list, but as of 2020, the artificial sweetener has been reviewed by the following agencies:
Whether aspartame should continue to receive scrutiny is still widely debated, and there may not be an end in sight.
However, the majority of trusted agencies agree that unless you’re guzzling more than 10 diet sodas a day, you likely will not get cancer from aspartame.
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