The bittersweet effects of sweeteners on the microbiome

Sweeteners are widely used

Sweeteners bind to the taste receptors on our tongue to create the perception of "sweet". They are often several hundred times sweeter than household sugar and yet have few or no calories.

As a result, sweeteners are widely used in our everyday lives. They are found in numerous "light" products or foods labelled as "sugar-free" and can be found in soft drinks, sweets, chewing gum and even toothpaste.

Which sweeteners are authorised in the EU?

There are currently 12 sweeteners authorised in the EU (1):

• Acesulfame K (E 950)
• Aspartame (E 951)
• Cyclamate (E 952)
• Saccharin (E 954)
• Sucralose (E955)
• Thaumatin (E957)
• Neohesperidin DC (E 959)
• Steviol glycosides from stevia (E960a)
• Enzymatically produced steviol glycosides (E960c)
• Neotame (E961)
• Aspartame-acesulfame salt (E 962)

For each of these substances there is a so-called ADI value (Acceptable Daily Intake). This value describes the maximum daily intake that is classified as safe for regular consumption.

However, the authorised sweeteners are currently being re-evaluated by the European Food Safety Authority (EFSA), as the original authorisations and ADI values are based on outdated study results.

Sweeteners vs. sugar substitutes

Alongside sweeteners, sugar substitutes are another type of artificial sweeteners. Chemically speaking, these are sugar alcohols. Well-known examples are erythritol, xylitol (birch sugar), sorbitol, mannitol and isomalt.

With the exception of erythritol, sugar substitutes are not calorie-free. However, they have significantly fewer calories than sugar and are therefore also used to reduce calories. In contrast to sweeteners, there are no ADI values for sugar substitutes. However, as they can have a laxative effect in larger quantities (more than 20 to 30 g per day), there is a corresponding warning on the packaging.

Numerous studies warn against sweeteners

The health effects of sweeteners and sugar substitutes have already been investigated in many studies. For sweeteners in particular, there are various research findings that point to health risks. An imbalance in the intestinal flora could be a central mechanism of these harmful effects.

Study: Sweeteners damage the human microbiome

In the following, we would like to present a study published in the journal Cell in 2022, which investigated the effects of four different commonly used sweeteners on the human microbiome (2).

Structure of the study

120 healthy adults between the ages of 26 and 35 were selected as test subjects for the study. In order to rule out any falsification of the study results, a dietary questionnaire was used to ensure that only people who did not consume artificial sweeteners in their normal diet were included in the study.

The test subjects were divided into six groups of 20 people each. Four groups consumed six commercially available sachets of aspartame, saccharin, sucralose or stevia every day for 14 days. The sachets were taken regularly throughout the day.

As glucose was mixed into the sweetener sachets as a filler, a fifth group received the same amount of glucose (5 g) as was present in the sachets, while the sixth group took nothing.

The following amounts of sweeteners were consumed daily:

• Aspartame: 240 mg (corresponds to 8 % of the ADI value based on 60 kg body weight)
• Saccharin: 180 mg (20 % of the ADI value)
• Sucralose: 102 mg (34 % of the ADI value)
• Stevia: 180 mg (75 % of the ADI value)

The quantities of sweeteners consumed (with the exception of stevia) were therefore well below the authorised ADI values.

In order to determine the effect of the sweeteners on blood glucose regulation, the participants wore a continuous glucose meter for the duration of the study. Glucose tolerance tests were also carried out on certain days. Stool and saliva samples were also analysed several times before, during and after the intake period to examine the microbiome.

Sweeteners influence the microbiome

All four sweeteners tested had an effect on the composition or metabolic activity of the microbiome, both in the gut and in the oral cavity.

The composition of the bacterial species changed the most with sucralose and saccharin. The activity of various bacterial metabolic pathways was altered in a variety of ways by all the sweeteners. There were no changes in the microbiome in the control groups that had only taken glucose or nothing at all.

Blood sugar regulation problems

The sweeteners ingested not only influenced the microbiome, but also the results of the glucose tolerance tests that were carried out multiple times. For example, the participants who had taken sucralose or saccharin showed significantly higher blood sugar peaks compared to the subjects in the other groups. In the week following the intake period, blood glucose regulation gradually normalised.

This suggests that sucralose and saccharin in particular could cause glucose intolerance or even insulin resistance if taken over a longer period of time and therefore contribute to the development of type II diabetes.

Changes in intestinal flora can cause glucose intolerance

An experiment with germ-free mice was conducted as part of the study to prove the connection between the administered sweeteners, the altered intestinal flora and the resulting glucose intolerance.

The scientists administered intestinal bacteria from the test subjects' faeces to the mice. The animals that had received microorganisms from people with impaired blood glucose regulation also showed an increased blood glucose level after a glucose tolerance test. The mice that had received microbes from people with normal blood sugar regulation were also able to regulate their blood sugar levels normally.

Conclusion: Sweeteners are harmful even below the ADI value

The study presented shows clearly that sweeteners can have harmful effects on human health even at levels well below the current ADI. Each of these substances interacts with the microbiome in different ways and the possible long-term effects on health are still largely unexplored. It is clear that artificial sweeteners are not a healthy substitute for household sugar and that their use, like the use of sugar, should be severely restricted.

Sources

1. Sweetener: What are sweeteners and sugar substitutes? Verbraucherzentrale [Internet]. 10.01.2024 [accessed on: 31.01.2024].
2. Suez J, Cohen Y, Valdés-Mas R, et al. Personalised microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance. Cell. 2022;185(18):3307-3328.e19.