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Home » There is little evidence that aspartame causes cancer

There is little evidence that aspartame causes cancer

Recently, the World Health Organization (WHO) has sent out mixed messages about whether aspartame causes cancer. The International Agency for Research on Cancer (IARC), a semi-autonomous organization within WHO, wants to categorize aspartame as a potential carcinogen.

On the other hand, a second expert WHO committee, the Joint Food and Agriculture Organisation/WHO Expert Committee on Food Additives (JECFA), considered both evidence of harm and the actual level of risk, and said there was no reason to change guidance. They state that the average human can safely consume up to 14 cans of diet drink a day.

I’m on the side of JECFA because powerful evidence shows no link between aspartame and cancer. This is unsurprising because IARC has declared substances as “carcinogens” based on very weak evidence.

This article will review aspartame and cancer, and what I think about the conclusions from both groups.

Photo by Matt Seymour on Unsplash

All about aspartame

Aspartame, which goes by the brand name Nutrasweet, although generic aspartame is also available, is a popular artificial sweetener, approximately 200 times sweeter than ordinary table sugar or sucrose. Aspartame is a dipeptide of two natural amino acidsLaspartic acid and Lphenylalanine. Since amino acids are the basic building blocks of every protein in every organism on this planet, these two amino acids are consumed regularly whenever we eat any plant or animal. Aspartic acid and phenylalanine are not unusual or unique amino acids, they are, in fact, quite common.

So, let’s be clear, in case the above wasn’t. All amino acids in all life on this planet are the same. Whether those amino acids come from aspartame or your steak or your blueberry-kale smoothie is irrelevant to the body. There’s no magical difference between your “natural” food’s aspartic acid and phenylalanine and that found in Nutrasweet.

Time to get even more science in this article. When aspartame is ingested while drinking your Diet Coke, it is hydrolyzed (broken down by water molecules) into its constituent components — aspartate, phenylalanine, and methanol, in an approximate 4:5:1 ratio. No aspartame has been found in the bloodstream since it is so quickly hydrolyzed in the gut, and only the constituent components are absorbed by the digestive system. And there are probably no transport mechanisms that can transfer aspartame from the gut to the bloodstream.

Again, let’s be clear. Aspartame itself doesn’t get into the blood, only the constituent amino acids do. This is the first problem with many false claims about aspartame — it is broken down in the gut into simple amino acids absorbed by the body and then utilized to build new proteins that your body requires.

Setting aside the absolute safety of the amino acids (the body self-regulates amino acid production and usage), the one concern could be the methanol formed during the hydrolysis reaction in the gut. Except for the fact that most fruit juices, and the human body itself, produces much more methanol than can be consumed in many cans of diet soda.

The methanol produced by the metabolism of aspartame is absorbed and quickly converted into formaldehyde and then completely oxidized to formic acid. The methanol from aspartame is unlikely to be a safety concern. Moreover, methanol is not stored in the body, it is metabolized and then excreted. The only way for methanol to have a toxic effect is to ingest an amount so large that it temporarily cannot be cleared from the bloodstream and causes harm.

Here’s some math. A 12 US fluid ounce (355 ml) can of diet soda contains 180 milligrams (0.0063 oz) of aspartame. That means that a can of diet coke could produce 18 mg of methanol when digested, an amount substantially below the dose of 7 g of methanol that is considered harmful. It is around 0.26% of the dangerous dose. And remember, it is the dose that makes the poison.

Back to the amino acids. There just are no plausible pathways that small amounts of simple amino acids, substances that are prevalent throughout all food sources, and a tiny amount of methanol, a substance also found widely in fruits and vegetables, and is manufactured by the body as a byproduct of numerous metabolic processes, could have any effect on anyone. Those two amino acids will just be absorbed by humans and utilized to manufacture any of the thousands of proteins in the body.

Just to cover all the bases, aspartame must be avoided by people with a rare genetic mutation, called phenylketonuria, which leads to an inability to metabolize phenylalanine properly. But those with this disease not only must avoid aspartame, but also any protein that contains that amino acid. These individuals have a very restricted diet that only allows them to consume certain proteins.

One final point. I don’t care if you think that aspartame tastes good or bad, it’s not the point of this article. If you want to argue this subjective point, it has nothing to do with the article. I don’t mind aspartame, and in a blind taste test, I can tell the difference between a beverage sweetened with it or sugar. But they both taste good, so I will take aspartame or any other non-nutritive sweetener.

clear drinking glass on black table
Photo by Joey Nguyễn on

Safety of aspartame

Despite this overall lack of plausibility, aspartame dangers have been subject to pseudoscientific attacks almost from the day it launched. Internet hoaxes, government investigations, and unscientific studies have continued to make it appear there might be an issue with aspartame.

That’s why we have real science. The Scientific Opinion on the re-evaluation of aspartame (E 951) as a food additive (pdf), published by the European Food Safety Authority (EFSA), came to the following scientific consensus:

  • The amount of aspartame that is absorbed into the bloodstream is nonexistent in numerous human and animal studies. This supports the understanding that aspartame is hydrolyzed into its simple, widely consumed, and common constituent amino acids in the digestive tract.
  • Scientists have found no acute toxic effects of aspartame.
  • The available data did not indicate that aspartame had any genotoxic effect.
  • There were no aspartame-related increases in neoplasms and tumors in carcinogenicity studies.
  • They did recognize some studies indicated that aspartame should not be consumed in large quantities by pregnant women, not necessarily because of the aspartame itself, but possibly because of gastrointestinal disturbances and the quality of the overall diet. They established that the potentially harmful dose of aspartame is 1000 mg/kg/day, a few hundred cans of diet soda per day.
  • They noted that there was no epidemiological evidence for potential associations between the consumption of aspartame and cancers.
  • Data did not support the genotoxicity of the methanol metabolite of aspartame.

And here is some of the vast body of research between aspartame and numerous health conditions:

  • Aspartame and obesity. No evidence.
  • Aspartame and gut biome. The gut microbiome has become the conspiracy theory of nutrition — it is the claim that is made to prove that something is dangerous despite the very weak evidence.
  • Aspartame and glucose intolerance. Once again, the lack of evidence in human clinical studies is remarkably lacking.
  • Aspartame and type 2 diabetes. No evidence.
  • Aspartame and migraines. Researchers propose it’s a placebo effect.

Overall, aspartame appears to be safe, with most claims being debunked. And as I wrote above, the WHO’s own JEFCA committee, which is also made up of scientists, still shows evidence that consuming 14 cans of diet soda per day is not going to cause harm. Of course, if you’re drinking 14 cans of diet soda per day, we should discuss your beverage choices to look at some alternatives.

Aspartame and cancer

OK, let’s get down to the WHO’s International Agency for Research on Cancer (IARC) recommending that aspartame be considered to be a cancer-causing agent.

I have had issues with IARC before because I think they ignore published, high-quality evidence that a particular substance does not cause cancer, instead cherry-picking evidence that says it does. And I feel like they’ve done the same thing here.

Here is just some evidence that does not support the claim that aspartame causes cancer:

  • A large meta-analysis (considered at the top of the hierarchy of biomedical research) concludes that “The aggregate effect sizes suggest that APM (aspartame) consumption has no significant carcinogenic effect in rodents.”
  • A large Spanish case-control study concluded that “We did not find associations between the use of AS (artificial sweeteners) and cancer.” On the other hand, did find increases in cancer risk in diabetic individuals that consumed aspartame. However, diabetes is a risk factor for all cancers, so it would be difficult to determine if aspartame or diabetes itself increased the risk of cancer.
  • In a large systematic review (also considered the pinnacle of the hierarchy of medical research), the authors concluded that “Based on the review of both the experimental data on genotoxicity or carcinogenicity of the specific NSS (non-nutritive sweeteners) evaluated, and the epidemiological studies it can be concluded that there is no evidence of cancer risk associated to NSS consumption.”
  • In another systematic review of human and animal studies, researchers concluded that “Taken together, available evidence supports that aspartame consumption is not carcinogenic in humans.”


I could go on and on, boring the reader with scientific research that disputes a link between aspartame and cancer. Yet, IARC is going to list it as a carcinogen, despite another WHO committee stating it’s safe.

And even if you do read an article that claims that there is a link between artificial sweeteners and some health conditions, like cancer, it’s difficult to determine whether the artificial sweetener caused cancer.

One of the issues of this type of research is reverse causality, which means that the researchers have no way of knowing if the people who drank 14 cans of diet soda per day and got cancer chose to drink those 14 cans of diet soda because the real cause of their cancer led them to that choice. Most people who consume diet soda are generally obese, which has been closely linked to all types of cancer.

I think IARC uses the precautionary principle in its decisions — even weak evidence makes them think “better safe than sorry,” and then add something to its list of carcinogens. But that’s not good science.

I know all of this science sounds like there is a huge amount of confusion regarding aspartame. I don’t think there is, I think the science solidly concludes that aspartame is not linked to cancer.


Michael Simpson

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