Sweets Eaten During Antibiotics Tied to Worse Loss of Gut Bacteria

Researchers at Memorial Sloan Kettering Cancer Center in New York tracked 9,419 meals eaten by 173 patients hospitalized for a blood stem cell transplant and report in Nature that sweets eaten while patients were on broad-spectrum antibiotics were linked to a sharper disruption of their gut bacteria.

The team says the finding points to something a hospital could test directly: whether cutting back on simple sugars for a short stretch during antibiotic treatment protects the gut community. The authors call the association surprising, because sugar-rich nutritional drinks are commonly recommended to transplant patients.

The study was published in Nature on Sept. 30, 2026. Of those patients, 158 also gave repeated stool samples, which the authors paired with the meal records. For every extra 100 grams of sweets eaten in the two days before a sample from a patient on broad-spectrum antibiotics, the model predicted a further 24.1% drop in bacterial variety compared with samples taken without that antibiotic exposure, an association and not a demonstrated cause. Sweets alone, in patients not on those drugs, showed no such association.

The group then tested the idea in mice. Animals given a single injection of an antibiotic developed a bloom of Enterococcus, a gut bacterium that can cause bloodstream infections. When those mice also got table sugar, the bloom was 16.3-fold greater at day three and 33.4-fold greater at day six than with the antibiotic alone. Sugar on its own, without the antibiotic, did not change Enterococcus levels in the mice.

In germ-free mice carrying nothing but a single Enterococcus strain, sugar made no difference, which the authors read as a sign that the effect needs a full gut community that antibiotics have already disturbed.

Every patient in the cohort received at least one antibiotic while their meals were being recorded, and most were switched to broad-spectrum drugs after a fever or another sign of infection.