If you believe everything you read on the internet, then is seems that a chemical found in thousands of products is causing an epidemic of severe neurological and systemic diseases, like multiple sclerosis and lupus. The FDA, the companies that make the product, and the “medical industrial complex” all know about the dangers of this chemical but are hiding the truth from the public in order to protect corporate profits and avoid the pesky paper work that would accompany the truth being revealed. The only glimmer of hope is a dedicated band of bloggers and anonymous e-mail chain letter authors who aren’t afraid to speak the truth. Armed with the latest anecdotal evidence, unverified speculation, and scientifically implausible claims, they have been tirelessly ranting about the evils of this chemical for years. Undeterred by the countless published studies manufactured by the food cartel that show this chemical is safe, they continue to protect the public by spreading baseless fear and hysteria.

Hopefully, you don’t believe everything you read on the internet, and you don’t get your science news from e-mail SPAM, where the above scenario is a common theme. While there are many manifestations of this type of urban legend, I am speaking specifically about aspartame – an artificial sweetener used since the early 1980s. The notion that aspartame is unsafe has been circulating almost since it first appeared, and like rumors and misinformation have a tendency to do, fears surrounding aspartame have taken on a life of their own.

I am frequently asked my opinion about the safety of aspartame. Nutritionists often council to avoid the sweetener, citing unverified claims that it is unsafe. I was recently sent a chain letter warning that aspartame causes MS (which of course can be cured by simply avoiding aspartame), and Snopes informs me that this particular letter first appeared in 1998.

There are also hundreds of websites dedicated to smearing this much abused food additive. One site, run by Dr. Janet Starr Hull (she has a doctorate in Nutrition), responds to the latest report of aspartame’s safety by writing:

I will never accept the news of aspartame safety. I think it is a “business” decision to discredit/discount the research results that aspartame DOES cause cancer, major nerve disorders, birth defects, and brain imbalances. Think about it – can you imagine the chaos that will occur when the truth of aspartame dangers is accredited. The FDA has known about the dangers, the corporations have known about the dangers, and the medical community (if it is really worth anything) has known about the dangers.

The statement that “nothing will ever convince me” is a huge red flag that someone is defending an ideological position, one immune to evidence or reason. Admittedly, in context it could be a clumsy statement that something is very unlikely. It would be very difficult to convince me that the earth is flat – I’m really saying that the existence evidence is overwhelming that the earth is not flat. But that is not what Dr. Hull is saying. She is specifically saying that she will dismiss any evidence that is contrary to her belief that aspartame is not safe on the a-priori basis that such disconfirming evidence is part of a vast conspiracy.

Of course, Dr. Hull also sells an aspartame detox kit, which might lead a cynical person to conclude that she cares more about selling alternative health products and stoking her sales with some unreasonable fear than about scientific evidence.

What evidence does she have for such a conspiracy? The argument from final consequences logical fallacy – big industry wouldn’t want it. It’s also not very plausible. Products get pulled from the market all the time when new evidence suggests they are not safe. Also, the final safety net for the consumer is legal liability. Class action law suits have bankrupted companies, even when the underlying claims were false. Imagine if they were true. Look how much the tobacco industry has had to fork over.

Now I am not arguing that corporations are all good corporate citizens or wouldn’t dream of sweeping some inconvenient evidence under the carpet. But I am saying that a decades long conspiracy among industry, federal regulatory agencies, the medical community, and multiple research institutions and individual researchers – all under the nose of the press and lawyers looking for big class-action suits – is implausible in the extreme. I am also arguing that we should fairly assess all the evidence, not just cherry pick the evidence we like and dismiss the rest out of hand.

What does the evidence say about aspartame? A recent published review of all available evidence, including hundreds of studies, concluded:

The studies provide no evidence to support an association between aspartame and cancer in any tissue. The weight of existing evidence is that aspartame is safe at current levels of consumption as a nonnutritive sweetener.

Multiple reviews, going back to 1985, conclude the same thing. Since this latest review there have been more studies, in various countries (how big is this conspiracy?), showing no link between aspartame and brain cancer, and a lack of correlation between artificial sweeteners and gastric, pancreatic, and endometrial cancers.

Like all such research, there is noise in the data (but no apparent signal). There is no pattern of evidence to suggest that aspartame causes cancer, autoimmune disease, neurological disease, diabetes, or anything else its critics claim. What legitimate scientific controversy there is comes from the animal data, mostly in rats. Here the evidence for a carcinogenic or genotoxic (causing changes in the DNA) effect of aspartame is mixed and requires careful review. Some effects, such as a dose-dependent effect on renal tumors, are specific to rats and do not translate to humans. Other studies are plagued by significant flaws, such as properly calculating doses (a big issue when trying to extrapolate doses from rats to humans). And still others show flat effects without a dose response curve, suggesting that a confounding factor, and not aspartame, is responsible for any observed increase in tumors.

For example, the European Food Safety Authority (EFSA) recently reviewed a 2005 study by the European Ramazzini Foundation of aspartame in rats showing increases in various neoplasms. They found multiple significant flaws, as described above, and concluded:

The data on total malignant tumours do not provide evidence of a carcinogenic potential of aspartame.

As I have noted before – you have to interpret a literature, not a single study. The results of one lab or one study can be erroneous. When decades have produced hundreds of studies on a question, the cherry pickers will always have a lot to choose from. That is why systematic reviews are necessary, and it is also necessary to understand the strengths and weaknesses of each type of research. In this case studies in humans have found no cancer risk from aspartame. Animals studies are problematic and have produced mixed results, but no clear evidence of a neoplastic risk.

A separate question is whether or not aspartame causes headaches in some people. While there is not a lot of specific data on this, there are case reports of aspartame triggering migraines in susceptible people. Migraineurs frequently have multiple food triggers, and there is a long list of foods known to be potential migraine triggers. This is not evidence for toxicity. So while evidence is lacking to demonstrate aspartame is a headache trigger, this is not implausible and not particularly worrisome. What I recommend to patients with frequent headaches is to keep a headache diary, rather than trusting to memory (and confirmation bias) to detect real associations. If there is a clear pattern between a potential trigger and headaches, then avoid that trigger.

Yet another distinct question about artificial sweeteners (not just aspartame) is whether or not they contribute to obesity by interfering with brain’s association between sweetness and calories. The theory is that using zero-calorie sweeteners dissociates the sensation of sweetness from caloric intake, so that sweetness will cause less satiety, leading to increases in overall sugar and calorie consumption.

The question of aspartame and weight control is a complex one, and can be approached from many research angles. Here is a recent review of research. At present the question is very much unsettled. It seems that there is no significant metabolic and no demonstrated neuronal effect from artificial sweeteners. However, people who knowingly consume diet drinks do tend to overcompensate by consuming greater calories overall. While studies of substituting aspartame for sugar in a blinded fashion show that calories are reduced, contributing to weight loss.

By my reading, the current summary of available research is that consuming calories in drinks contributes to weight gain and obesity, substituting calorie-free drinks (whether water or diet drinks containing artificial sweeteners) does help reduce caloric intake and aid in weight control, but there is a tendency to overcompensate by increasing other caloric intake. Therefore it seems reasonable to use artificial sweeteners to reduce caloric intake from drinks, but to be careful to control overall caloric intake (so no, putting aspartame in your coffee does not mean you can eat the cheesecake).


Aspartame is a highly studied food additive with decades of research showing that it is safe for human consumption. As expected, the research is complex making it possible to cherry pick and misinterpret individual studies in order to fear monger. But the totality of research, reviewed by many independent agencies and expert panels, supports the safety of aspartame.

A conspiracy to hide the risks of aspartame, however, remains a popular internet urban legend that will likely not disappear anytime soon.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the president and co-founder of the New England Skeptical Society, the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also contributes every Sunday to The Rogues Gallery, the official blog of the SGU.