Artificial sugars in low-calorie drinks could be bad for your gut, study suggests

Sweeteners found in sugar-free soft drinks could slow the growth of beneficial gut bacteria, a study suggests.

Researchers from the University of Cambridge studied how artificial and low‑calorie sweeteners affect the bacteria living in the gut, and how these effects change when they are eaten together with caffeine, flavourings or medicines.

While marketed as healthier alternatives to sugar, there is growing evidence linking sweeteners in food and drinks to diseases such as type 2 diabetes, obesity and cancer.

Sugar substitutes are not digested in the same way as sugar because they pass through the stomach and interact directly with the bacteria living in a person’s intestines.

The researchers grew each of the 25 gut bacterial species – including beneficial, neutral and potentially harmful bacteria – in the lab. 

They then exposed each culture individually to 39 common, commercially used sweeteners, some artificial and others natural, and measured how well the bacteria multiplied.

The research, published in the journal Molecular Systems Biology, found that one sweetener derived from the stevia plant, isosteviol, significantly impaired the growth of certain gut bacteria when combined with the antidepressant duloxetine.

Duloxetine is the seventh most dispensed antidepressant in the UK, with more than five million NHS prescription items issued annually. 

When the two were combined, researchers found the sweetener strongly suppressed two gut bacteria that play important roles in maintaining a healthy gut microbiome.

Further analysis showed the combination increased toxicity in certain laboratory-grown cells and interfered with cells involved in the body’s inflammation and immune responses.

‘Sweeteners are often marketed as metabolically neutral, but our study challenges this idea,’ said study lead author Dr Sonja Blasche. 

‘We found they can directly affect gut bacteria, particularly when mixed with other compounds such as medication and food additives.’ 

More research is needed, she said.