Eating a lot of sugar while taking antibiotics may worsen damage to the gut microbiome, according to a study published in the journal Nature. Researchers tracked 9,419 meals eaten by 173 hospitalised patients with blood cancers, along with daily stool samples.

They found that for every additional 100 grams of sugar consumed in the 48 hours before antibiotic treatment, gut microbial diversity fell by a further 21 per cent. Lower diversity leaves the gut more vulnerable because fewer helpful bacteria remain to compete with harmful ones.

High sugar intake combined with antibiotics was also linked to more Enterococcus faecium, a bacterium tied to difficult-to-treat infections. Mouse experiments showed a similar pattern: sucrose plus the antibiotic biapenem drove Enterococcus levels up 16.3 times by day three and 33.4 times by day six.

The study was led by researchers from NYU Langone Health, City of Hope and Memorial Sloan Kettering. The authors stress the human findings are observational and call for clinical trials before any dietary advice changes.