Is Aspartame Bad For You?

Lucy Bell-Young

by Lucy Bell-Young

29th August 2018

Artificial sweeteners, like aspartame, are found everywhere. From your favourite dessert to your favourite can of soda, sweeteners are one of the most common food additives in the world. These sugar-substitutes have a pretty bad reputation, but can their dangers to our health be supported by science?

About Artificial Sweeteners

Artificial sweeteners are sugar substitutes that contain little to no calories and are just as sweet, if not sweeter than table sugar (a.k.a. sucrose). There are several types of sweeteners:

  • Acesulfame Potassium has the E-Number E950 and is 200 times sweeter than sucrose and just as sweet as aspartame. It is commonly used in baking because of its heat stability
  • Aspartame has the E-Number E951 and is 200 times sweeter than sucrose
  • Saccharin has the E-Number E954 and is up to 400 times as sweet as sucrose. It is also very heat stable and is often used with aspartame to ensure the product stays sweeter for longer
  • Sucralose has the E-Number E955 and is one of the most common artificial sweeteners. It is up to 1,000 times sweeter than sucrose and 3 times as sweet as aspartame

Other artificial sweeteners include cyclamate, stevia, sorbitol and xylitol. These food additives are used in thousands of products, from cakes and drinks to ready-meals and even toothpaste. So why do they have such a bad reputation?

While the FDA, EFSA as well as Cancer Research have all declared that artificial sweeteners are safe for human consumption, this has not managed to quell the accusations that sweeteners cause cancer, diabetes, brain damage and heart syndrome.

This would be a very long blog if we looked into each individual sweetener, so today we’re focussing our efforts on the science behind one of the most maligned sweeteners of all: aspartame.

Brown sugar cubs in a small kilner jar on a table

There are many different types of artificial sweetener, including saccharin, aspartame and sucralose, which is up to 1,000 sweeter than normal table sugar.

What is Aspartame?

This sweetener is one of the most notorious ingredients in fizzy drinks. Chemically, it is a methyl ester of the aspartic acid and phenylalanine dipeptide and is also known as 1-methyl ester.


The controversy surrounding this sugar substitute has forced the FDA to conduct over 500 studies on the sweetener, making it one of the most studied food additives to date. The drink manufacturers, Pepsi, even went as far as to remove aspartame from their beverages in 2015.

However, this wasn’t due to its alleged health risks but rather because of consumer concerns, and Pepsi is now even reversing its decision and reintroducing aspartame into its drinks.

What Are the Dangers of Aspartame?

Aspartame has been accused of causing cancer, seizures, brain damage, neurotoxicity and many more evils. None of these claims have been substantiated by science, however, and often do not have reliable data to really spearhead an attack on the sweetener.

Despite the abundance of clinical studies that disprove the association between aspartame and serious health risks, people still think this sweetener should be avoided like the plague. So what does it actually do to our bodies to cause such controversy?

Rows of glass bottles of Pepsi, which contain aspartame

In 2015, following consumer concern, Pepsi removed aspartame from their Diet Pepsi formula. Now, in 2018, they are reintroducing the sweetener given that the FDA have declared it safe for humans.

Aspartame in the Body

When aspartame is consumed, it travels to the small intestine where it is rapidly hydrolysed and broken down. This breakdown happens so quickly that even when high doses of the sweetener are ingested, there are no traces of it in the blood.

The breakdown products of aspartame are aspartic acid, phenylalanine and methanol in a mass ratio of 4:5:1. It is the breakdown that forms the basis of many people’s concerns.

Aspartic Acid

Also known as aspartate, aspartic acid is one of the most common amino acids that is produced by a typical diet. Nearly everything we eat contains a whole lot of aspartic acid, including but not limited to:

  • Dairy products
  • Whey protein or protein supplements
  • Meat and poultry
  • Many types of fish, like salmon or mackerel
  • Nuts and cereals

The production of aspartic acid via aspartame only makes up 1 – 2% of our daily intake, a very insignificant amount when compared to other food sources that contain more of the amino acid.

Nevertheless, people have been quick to condemn aspartame as inflicting damage to the brain and nerve cells. This is based on the belief that the aspartic acid produced by the breakdown of this sweetener is capable of over-stimulating glutamate to cause excitotoxicity.

However, given the extremely low production of aspartic acid from aspartame, as well as the sweetener undergoing a rapid breakdown, clinical studies have concluded that there are no neurotoxic effects associated with aspartame. In fact, its production of aspartic acid in the body is actually more beneficial than it is harmful.


The main danger associated with aspartame is the fact that it is converted to methanol in the body. Also known as methyl alcohol, methanol (CH3OH) is the simplest of all alcohols and is incredibly toxic to humans.

Industrially produced by the hydrogenation of carbon monoxide, methanol is commonly used as a precursor to chemicals like acetic acid and formaldehyde. As little as 10ml of pure methanol can destroy the optic nerve and cause permanent blindness; 30ml is potentially fatal.

The lethal dose of this chemical is approximately 1-2ml of methanol per kg of body weight. The fact that aspartame gets converted into this toxic substance sounds scary at first, but not when you take into account that the methanol produced in this way is not enough to cause negative health effects. There is even less methanol in aspartame than there is in a glass of red wine:

  • Only 10% of aspartame in a drink gets converted into methanol
  • 10% is the equivalent of 55 mg of methanol per litre
  • This level of methanol is much lower than other sources that contain methanol
  • Red wine contains 99-271 mg of methanol per litre
  • Tomato juice contains up to 218 mg of methanol per litre

Everything from cigarettes, fruit and vegetables to marmalades, chewing gum and smoked fish contain methanol, and often in higher concentrations than in aspartame. Therefore, even if you cut out artificial sweeteners altogether, you would still consume methanol every day.

Glasses of red wine on a table

There is a higher content of methanol in red wine than there is aspartame.


The methanol produced by the breakdown of aspartame is quickly metabolised into formaldehyde, which is converted to formate before leaving the body via urine.

Formaldehyde is extremely toxic to humans, and the conversion of methanol into this substance is one reason why methanol can be deadly. But you have nothing to worry about with aspartame.

Like with methanol, the levels of formaldehyde produced by the breakdown of aspartame are incredibly low. In fact, food sources that produce higher levels of formaldehyde in the body, like fruits or vegetables, have been classified as safe and have had no adverse health effects.


The only real cause for concern about this controversial sweetener is the presence of phenylalanine, both as a by-product and ingredient. Even so, the intake of this chemical is only dangerous for those who suffer from phenylketonuria.

Phenylketonuria is when the body is incapable of breaking down phenylalanine. The amino acid can then reach toxic levels in the body and has the potential to cause brain damage. This is why if a drink or food source contains phenylalanine, it must be clearly stated on the packaging.

However, for those who do not suffer from phenylketonuria, the contents of phenylalanine poses no danger as their bodies are able to effectively break it down.

Are there Any Health Risks?

At normal dietary levels, there are no negative health effects associated with aspartame. In other words, as long as you drink less than 32 cans of soda a day, you’re in the clear!

There is a range of health risks that continue to be attributed to this food additive. The age-old rumour that it is a carcinogen gained popularity after an Italian institute claimed to have evidence that proved the sweetener caused cancer.

However, this study was quickly deemed as heavily bias and very unreliable, especially given that they refused to provide the FDA with their data. Since then, clinical studies have shown that there is no association between aspartame and cancer.

Many people also claim that aspartame causes headaches, another connection that has been disproven. Studies conducted on the link between aspartame and headaches found that when the participants knew they were taking aspartame, they reported having headaches 100% of the time. When they were given a placebo and didn’t know whether they were taking aspartame, this percentage dropped to 35%.

Fizzy drink bottles in a vending machine

So there you have it. Thanks to science, we know that aspartame is not associated with having any negative health effects, and it doesn’t deserve the reputation it gets as a dangerous substance. But as with every guilty pleasure we enjoy, like chocolate, crisps, a take-out or your favourite alcoholic drink, aspartame may not be bad for you – but it isn’t good for you, either!


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