A round of antibiotics for a sinus infection or a bad throat, with a few cookies or a soda along the way to feel a little better.
For most of us, the diet keeps running on autopilot.
New research in Nature suggests that habit may matter more than anyone expected.
Sugar eaten during an antibiotic course appears to sharply amplify the damage the medication already does to your gut bacteria.
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The study, published September 30, 2026, followed 173 hospitalized cancer patients and tracked 9,419 of their meals alongside daily gut samples.
For every 100 grams of sugar eaten in the 48 hours before an antibiotic dose, bacterial diversity in the gut fell by about 21 percent further than antibiotics alone would cause.
Outside the antibiotic window, the same amount of sugar had no measurable effect on the microbiome.
The combination was the problem.
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Why the combination matters
A healthy gut hosts hundreds of different bacterial species.
That variety is called alpha diversity, and losing it leaves fewer helpful microbes to keep harmful ones in check.
Antibiotics already thin out that community. The new work suggests sugar then accelerates the collapse by feeding the few species that survive.
One of those survivors is Enterococcus faecium, a hospital-associated bacterium often resistant to treatment.
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It can trigger bloodstream and urinary tract infections.
In mice given the antibiotic biapenem together with sucrose in their drinking water, Enterococcus populations climbed 16.3-fold within three days.
By day six, the burden was 33.4-fold higher than in mice on antibiotics alone.
What this means if you are on antibiotics
The patients in the study were severely ill and more vulnerable than most people on a routine prescription.
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The researchers are not claiming the same scale of damage applies to a short course for a sinus infection.
Still, the biology is the same.
Jonas Schluter, assistant professor of microbiology at NYU Langone Health and co-senior author, said that cutting back on sweets during and after antibiotics may help limit the damage.
The target is added sugars.
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The researchers' sweets category covered foods like candies, baked goods and sugary drinks, the sort of items most people eat as extras rather than as part of a meal.
Cutting back for the week a prescription lasts is a change most people can manage.
Drinking water, eating fiber-rich foods, and holding off on the dessert and soda during that window is the practical version of what the researchers tested.
The team now plans a clinical trial to test whether short-term dietary changes during antibiotic treatment improve outcomes in patients.
Anyone starting a course of antibiotics can raise the question of diet with their prescribing doctor.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.