Antibiotics and Sugar Could Be A Very Bad Combination

You knew that antibiotics can harm the diversity of the intestinal microbiota and disrupt the important balance of good and bad bacteria. But this very important new study shows that consuming sugar during antibiotic therapy intensifies the effect and makes things even worse.

It is well established that the gut microbiota is important for many things, including digestion and immunity. Exciting new research has hugely expanded the resume with the discovery that the microbiota in your gut communicate with the cognitive and emotional centers of your brain. Everything from depression, anxiety, stress, insomnia and Alzheimer’s has been added to the list.

The growing awareness of the importance of the gut microbiota makes the also well established fact that antibiotics disrupt the gut microbiota even more important. An important new study adds a potentially crucial new bit of information.

This very well controlled study of blood cancer patients who were hospitalized for several weeks undergoing haematopoietic cell transplantation examined the effect of diet on antibiotics and disturbed gut microbiota. The researchers had the advantage of knowing exactly what the patients were eating on their controlled hospital diet.

They found two important things: one old and one new.

The no longer surprising discovery was that taking antibiotics was associated with shrunken bacterial diversity: that’s bad. The important new discovery was that sugar intake was associated with significantly worsening the decrease in diversity: for every 100g increase of sugar after antibiotics, there was an additional 24.1% decrease in microbiota diversity.

The combination of antibiotics and sugar not only made diversity in gut worse, it also encouraged the growth of dangerously bad bacteria, including, especially, Enterococcus faecium, an important cause of antibiotic-resistant bloodstream infections.

Clarifying the picture, the data showed that the culprit was not naturally occurring sugars like the ones found in whole food. The “key contributor” was added sugars.

A further disturbing discovery was the effect this pattern had on immunity. Patients on antibiotics who consumed above average intake of sugar had a 12% higher risk of mortality after their transplantation.

In some ways, the discovery of this damaging combo is not surprising. It has long been known that antibiotics and sugar can both foster bad bacteria. This important new study establishes that the combo of those two may be especially harmful.

Nature. 2026. doi.org/10.1038/s41586-026-11077-3.

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