Artificial sweeteners - harmfulness and side effects

In 2023, the World Health Organization (WHO) included the sweetener aspartame on the list of possible carcinogens (Group 2B) – i.e. substances for which there is limited evidence of carcinogenicity in humans , but not sufficient to confirm a direct causal relationship.
The move has reopened the debate over the safety of artificial sweeteners , which have been used for more than half a century. While they help reduce sugar intake, research shows that their health effects are inconclusive.

Why do some people reach for them?

Artificial sweeteners are used when we want to reduce sugar but maintain a sweet taste . They can be found in light or zero drinks, chewing gum, protein puddings and syrups.
These are chemically created substances with a sweetness many times higher than sucrose - and often with zero caloric value.

What they are and how they work

Artificial sweeteners are synthetic sugar substitutes that bind to the same taste receptors on the tongue as carbohydrates, creating a sweet sensation without providing significant energy.
However, their very high sweetness can disrupt the perception of natural tastes - the brain gets used to the intense sweetness, and ordinary foods can then seem "not very sweet".

How are they made?

Each sweetener has its own chemical manufacturing process. Here are a few examples:

• Aspartame (E951) – methyl ester of a dipeptide formed from L-aspartic acid and L-phenylalanine. During decomposition, a small amount of methanol is also produced, but well below the toxic threshold.

• Sucralose (E955) – produced by chlorination of sucrose . Most of the substance is not absorbed and leaves the body unchanged.

• Acesulfame K (E950) – synthesized by methylation of oxathiazine and neutralization with potassium. Often combined with aspartame to offset the bitter aftertaste.

Most commonly used artificial sweeteners

Are they safe?

Currently, the current evidence is not strong enough to prove that common amounts of aspartame or other permitted sweeteners have a carcinogenic effect.

• "The dose makes the poison": the average person would have to drink approximately 17–18 cans of Diet Coke per day to reach the acceptable daily intake (ADI).

• Observational studies are not causal: studies that find an association (correlation) with cancer do not prove cause (causality) – they may be influenced by other factors (diet, lifestyle).

• Both EFSA and FDA still confirm that aspartame and other sweeteners are safe within the permitted ADI .

Risks of long-term consumption

Based on current knowledge, three main areas need to be considered:

1. Gut microbiome – some sweeteners can alter the composition of the gut microbiota, which can affect glucose tolerance and metabolism.

2. Taste adaptation – frequent contact with extreme sweetness reduces sensitivity to naturally sweet foods.

3. Calorie compensation – people who drink “zero” beverages may subconsciously increase their calorie intake from other sources.

There is no convincing evidence yet that regular consumption of artificial sweeteners causes cancer, obesity, or metabolic syndrome – nor that their long-term use is completely risk-free.

Natural alternatives

Steviol glycosides (E960) are natural sweeteners obtained from the Stevia rebaudiana plant. They are approximately 200 times sweeter than sugar , contain no calories and are also suitable for diabetics .

According to a review by Ruiz-Ojeda et al. (2019), steviol glycosides are not absorbed in the small intestine , but rather in the colon, where gut bacteria break them down into steviol . This process may slightly affect the composition of the gut microbiome , particularly the Bacteroides bacteria that are involved in their breakdown.
However, these changes are very small and clinically insignificant , and the effect of stevia on the gut microbiota has not yet been sufficiently studied .

Compared to some synthetic sweeteners – such as saccharin or sucralose , which can be more disruptive to the microbiome – stevia appears to be a more gentle choice . However, it is advisable to adhere to the recommended daily intake (ADI) of 4 mg/kg body weight , which was set by the European Commission.

Summary and recommendations

Artificial sweeteners can be a useful tool if you're trying to limit your sugar intake and maintain a stable body weight . They help reduce energy intake, don't directly affect glucose levels, and can make it easier to transition from sugary drinks to a more balanced diet.

On the other hand, they are not without limits . Frequent consumption of highly sweet products can disrupt the natural perception of taste , affect the gut microbiome , and lead to calorie compensation - that is, a person simply makes up for the "saved" energy elsewhere.

In the long term, therefore, while artificial sweeteners are considered safe when used routinely , it is not advisable to rely on them as a permanent solution.

If you are concerned about aspartame or artificial sweeteners, it is possible to limit their amount or replace them with natural, non-energy sweeteners.

Resources

1. World Health Organization (2023): Aspartame hazard and risk assessment results.

2. Mooradian AD, Smith M., Tokuda M. (2017): The role of artificial and natural sweeteners in reducing the consumption of table sugar. Clinical Nutrition ESPEN, 21, 1–8.

3. Kossiva L., et al. (2024): Chronic Use of Artificial Sweeteners: Pros and Cons. Frontiers in Nutrition, PMC11435027.

4. Ruiz-Ojeda FJ, et al. (2019): Effects of Sweeteners on the Gut Microbiota: A Review of Experimental Studies and Clinical Trials. Advances in Nutrition, PMC6363527.