Updated 23rd April 2024

Aspartame: Why are we still talking about it?

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Aspartame is one of the most common artificial sweeteners. It’s consumed by millions of people every day.

Although it was first marketed more than half a century ago, amazingly, there are still open questions about its safety.

Because aspartame gives you a sweet hit with very few calories, experts initially hoped it might help reverse the rising tide of obesity and diabetes. 

ZOE has covered the divisive topic of artificial sweeteners elsewhere, so we won’t focus on it here. 

Instead, we’ll zero in on some of the health concerns about aspartame and ask why, after all these years, we’re still unsure about it. 

OK, we’ve got a lot to cover, so let’s start with the basics.

What and where is aspartame?

Aspartame is an artificial sweetener, and it’s around 200 times sweeter than sugar

It's also one of the most widely used artificial sweeteners in the United States and United Kingdom.

Aspartame is formed of two amino acids — the building blocks of protein. These are aspartic acid and phenylalanine.

As your body breaks down aspartame, this produces a tiny amount of methanol, a form of alcohol that also occurs naturally in fruits and vegetables.

Manufacturers can add aspartame to almost any product that they want to make sweet without using sugar. 

The only exceptions are products that need to be baked for a long time — high temperatures cause the sweetener to lose its sweetness. 

Aspartame is also in some medications and chewable vitamins.

In the European Union and U.K., you might find "aspartame” on products' labels or its E-number, which is E-951. 

In the United States, labels must state “aspartame” and acknowledge the presence of one of its breakdown products, phenylalanine.

Globally, aspartame is roundly deemed safe by regulatory bodies. These include the European Food Safety Association (EFSA), the U.S. Food and Drug Administration (FDA), Japan’s Ministry of Health, Labor, and Welfare, and Food Standards Australia New Zealand.

So, why the fuss?

Scientists have conducted many studies on aspartame, and as we’ve seen, global regulators assure us that it’s safe. Why are we still talking about aspartame?

As the authors of one review put it: 

“Although many studies have been performed to determine the health effects of aspartame, the results of its long-term use remain difficult to predict, and its use [...] remains controversial.”

The BMJ review

A review that appeared in The BMJ in 2019 looked at the health effects of artificial sweeteners, including aspartame. 

The scientists assessed 56 studies investigating various health outcomes, including diabetes, weight gain, blood sugar control, and cardiovascular disease.

Overall, they identified no health benefits or concerns associated with artificial sweeteners. 

However, they explain that “Of the few studies identified for each outcome, most had few participants, were of short duration, and their methodological and reporting quality was limited.”

Review of metabolic effects

The authors of another review looked specifically at metabolic outcomes associated with aspartame. 

In particular, they focused on fasting blood glucose levels, cholesterol, triglycerides (blood fats), body weight, and energy intake.

As with The BMJ review, the team found no significant benefits or dangers.

But once again, they write that because the studies they reviewed were so different, and some were small, the quality of evidence was only “moderate.”

The WHO review

To date, the most extensive review of artificial sweeteners came from the World Health Organization (WHO) in 2022. The authors looked at 283 studies, many of which included aspartame.

They conclude, “There is [a] suggestion of negative health effects with long-term use, but the evidence is ultimately inconclusive.”

According to the study, these negative health effects include an increased risk of “obesity, type 2 diabetes, cardiovascular diseases, and mortality.”

So, this is why we’re still talking about aspartame.

Although it has been studied a great deal, we need larger and longer trials, and the quality of the research needs to improve. 

For a compound that many of us consume daily, we need water-tight safety information.

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Other links to health

The health risks associated with aspartame aren't limited to metabolic conditions, either. Next, we’ll run through some other concerns that deserve more research and attention. 


Of all the conditions we’ll mention today, perhaps cancer's possible link with aspartame has received the most attention from researchers. And the debate isn’t over.

Scientists recently published a study that followed over 100,000 people for an average of 7.8 years. The authors concluded:

“Artificial sweeteners (especially aspartame and acesulfame-K), which are used in many food and beverage brands worldwide, were associated with increased cancer risk.”

Not all recent reviews agree. One from 2019 concludes that the “highest quality epidemiology studies do not support an increased risk of cancer.”

However, we have to be mindful of industry ties. That particular review was funded by the Calorie Control Council, which represents the “low- and reduced-calorie food and beverage industry.”

Vested financial interests like these muddy already murky scientific waters. We’ll touch on these financial ties again a little later.

Gut microbiome

Understanding how artificial sweeteners affect the gut microbiome is a relatively new area of study. 

And there are early signs that sweeteners, including aspartame, might influence the population of microbes in your gut.

We don’t know precisely what these changes might mean for your health. But we know that a healthy gut microbiome is linked to better overall health

It may be that the changes caused by aspartame don’t make a huge difference to your health, but we should certainly dig deeper.

ZOE has an article on artificial sweeteners and your gut microbiome if you’d like to learn more.

Brain and behavior

There’s some evidence that aspartame might influence brain health and behavior.

Earlier, we mentioned that when you eat aspartame, your body breaks it down into the amino acids phenylalanine and aspartic acid.

According to the authors of a review, when you consume aspartame — but not other protein sources containing these amino acids — it can boost levels of phenylalanine and aspartic acid in the brain

Once it's in your brain, phenylalanine can influence levels of your brain’s chemical messengers, called neurotransmitters.

And aspartic acid itself can act as a neurotransmitter.

You might remember that a small amount of methanol is produced when aspartame is broken down. As methanol is metabolized, it produces formaldehyde and formate, both of which are toxic to the brain.

As is the fashion in aspartame research, the review's authors concede that we need much more research.

Overall, they warn:

“Aspartame consumption needs to be approached with caution due to the possible effects on neurobehavioral health. Whether aspartame and its metabolites are safe for general consumption is still debatable due to a lack of consistent data.”

And more …

Scientists have concerns about aspartame’s influence on a wide range of other areas of health, including kidney and skin health. They're also concerned about possible links with neurodegenerative diseases, like Alzheimer’s, as well as allergies. 

In some cases, the possible link is theoretical or based on animal studies. So, without wanting to sound like a broken record, we need more research into aspartame. 

None of these concerns may turn out to be justified. But when we remember that millions, or perhaps billions, of people consume aspartame regularly, it’s surely worth checking. 

Especially when you consider that aspartame is not an essential nutrient, and it doesn't help keep our food safe — it just makes things sweeter.

So, if it poses a risk, it’s an unnecessary risk, however small.

How did aspartame get approved?

Aspartame is big business. And with big business, you’ll find big money, which wields big influence.

A recent Panorama documentary on ultra-processed food described some of the drama surrounding aspartame. 

Aired on the U.K.’s BBC, it featured ZOE’s Scientific Co-Founder Prof. Tim Spector and Chief Scientist Dr. Sarah Berry.

The documentary makers also interviewed Prof. Erik Millstone, a researcher and professor of science policy at the University of Sussex. He discussed how the EFSA had assessed aspartame’s safety.

As part of its review, the EFSA looked at available research into aspartame. But, according to Prof. Millstone, “About 90% of the reassuring studies were funded by large chemical corporations that manufacture and sell aspartame.”

Of course, those who profit from aspartame were more likely to conclude that it’s safe.

“There’s a pattern there that suggests the industry designs and conducts studies that provide reassuring evidence,” he continued. “I saw that as an expression of a very profound and dangerous bias.”

Also, in a 2017 paper, Prof. Millstone and his co-author explain that the EFSA's review had rejected all 73 studies that identified potential harm linked to aspartame — and it had accepted 84% of the studies that identified no harm.

The reviewers, they write, “favored commercial interests over consumer protection.” 

Meanwhile, the Corporate Europe Observatory, a nonprofit that tries to “expose any effects of corporate lobbying on E.U. policymaking,” also suggests that some panel members had financial conflicts of interest

What about the FDA?

The FDA approval process also seems to have been a little shady. According to Right To Know, a “nonprofit investigative public health research and journalism group,” there was trouble from the start.

It explains that even early studies had found links between aspartame and health concerns — and the industry-funded studies weren’t up to scratch.

The group also describes “revolving-door relationships between FDA officials and the food industry.”

Along similar lines, the authors of a paper on research bias observe:

“Among a sample of studies of aspartame, 100% of the industry-sponsored studies concluded that aspartame was safe, and 92% of the independently funded studies identified adverse effects of aspartame consumption.”

What should you do?

Entirely avoiding aspartame would be incredibly challenging, and it might not be necessary.

At ZOE, we know that a diet with a wide variety of plant-based foods is the healthiest choice. And it's less healthy to consume high amounts of ultra-processed foods, which are more likely to contain aspartame.

So, whenever you can, opt for fresh ingredients, fruits and vegetables, pulses, nuts, seeds, and the like. Aim to have 30 different plant foods each week.

That way, your intake of ultra-processed foods, and therefore aspartame, will naturally decline.

The take-home

In brief: Aspartame is a compound consumed by millions of people every day, and it might carry a variety of health risks. 

Despite long-standing interest from researchers and public concern, we still don’t know the precise dangers. 

Over the last few months, ZOE has covered the health effects of many common food additives, including flavorings, colorings, emulsifiers, and preservatives.

We’ve ended most of these features in a very similar way. It goes something like this:

Having small amounts of these additives every so often seems like it's probably safe for most people. But because everyone’s body is different, some people might be affected differently.

Importantly, we still have no idea whether consuming a complex cocktail of these additives daily for decades — as many of us do — affects our health.


Artificial sweeteners. (n.d.). https://www.uab.edu/shp/nutritiontrends/recipes-food-facts/food-facts/artificial-sweeteners 

Artificial sweeteners and cancer risk: Results from the NutriNet-Santé population-based cohort study. PLOS Medicine. (2022). https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003950 

Aspartame. (n.d.). https://www.efsa.europa.eu/en/topics/topic/aspartame 

Aspartame. (2022). https://www.foodstandards.gov.au/consumer/additives/aspartame/Pages/default.aspx 

Aspartame and other sweeteners in food. (2023). https://www.fda.gov/food/food-additives-petitions/aspartame-and-other-sweeteners-food 

Aspartame: Decades of science point to serious health risks. (2023). https://usrtk.org/sweeteners/aspartame_health_risks/ 

Aspartame — true or false? Narrative review of safety analysis of general use in products. Nutrients. (2021). https://www.mdpi.com/2072-6643/13/6/1957 

Association between intake of non-sugar sweeteners and health outcomes: systematic review and meta-analyses of randomised and non-randomised controlled trials and observational studies. The BMJ. (2019). https://www.bmj.com/content/364/bmj.k4718 

Code of Federal Regulations Title 21. (2023). https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=172.804 

Conflicts of interest scandals at EFSA: A non-exhaustive chronology of recent events. (n.d.). https://corporateeurope.org/en/food-and-agriculture/efsa/chronology 

EFSA’s toxicological assessment of aspartame: was it even-handedly trying to identify possible unreliable positives and unreliable negatives? Archives of Public Health. (2019). https://archpublichealth.biomedcentral.com/articles/10.1186/s13690-019-0355-z 

Evaluation of aspartame cancer epidemiology studies based on quality appraisal criteria. Regulatory Toxicology & Pharmacology. (2019). https://www.sciencedirect.com/science/article/pii/S0273230019300418 

Everything you need to know about aspartame. (2020). https://foodinsight.org/everything-you-need-to-know-about-aspartame/ 

Health effects of the use of non-sugar sweeteners: a systematic review and meta-analysis. (2022). https://www.who.int/publications/i/item/9789240046429 

List of designated additives. (2022). https://www.ffcr.or.jp/en/tenka/list-of-designated-additives/list-of-designated-additives.html 

Nephrotoxic effect of aspartame as an artificial sweetener: a brief review. Iranian Journal of Kidney Disease. (2017). https://pubmed.ncbi.nlm.nih.gov/29038387/ 

Neurophysiological symptoms and aspartame: What is the connection? Nutritional Neuroscience. (2017). https://www.tandfonline.com/doi/abs/10.1080/1028415X.2017.1288340 

Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance. Cell. (2022). https://www.sciencedirect.com/science/article/pii/S0092867422009199 

Relationship between research outcomes and risk of bias, study sponsorship, and author financial conflicts of interest in reviews of the effects of artificially sweetened beverages on weight outcomes: A systematic review of reviews. PLOS One. (2016). https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0162198 

Which artificial sweetener is right for me? (2023). https://www.diabetes.co.uk/sweeteners/which-artificial-sweetener-is-right-for-me.html 

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