Sugar May Supercharge Antibiotic Gut Damage Hospital Study Suggests

By Allison Proffitt

October 6, 2026 | Cutting back on sweets while taking antibiotics could help protect the gut’s bacterial community, according to a study published yesterday in Nature that compared what cancer patients ate to what was happening in their intestines.

Diet research on the microbiome has largely relied on healthy volunteers or long-term eating habits. But researchers in this study looked at the effects of specific foods that can be detected over a two-day window during acute illness (DOI:10.1038/s41586-026-11077-3).

Researchers at Memorial Sloan Kettering Cancer Center with colleagues from NYU Langone, City of Hope, and other institutions followed 173 adults hospitalized at Memorial Sloan Kettering Cancer Center for bone marrow transplants between 2017 and 2022. Transplant  patients are unusually good subjects for diet research. They stay in the hospital for weeks; eat hospital catering meals that can be categorized by research dieticians, weighed, and logged;  receive heavy doses of antibiotics; and give frequent stool samples. The team recorded 9,419 meals and analyzed 1,009 stool samples from 158 patients.

The researchers found that—as expected—broad-spectrum antibiotics (drugs like piperacillin-tazobactam, cefepime and carbapenems, given for fevers and infections) reduced the diversity of gut microbes. But when patients also consumed more sugary foods and drinks in the two days before a stool sample was collected, that sample showed that diversity fell further. For every additional 100 grams of sweets consumed, the model predicted an extra 24% drop in diversity in antibiotic-exposed samples.

To categorize food, the researchers considered the dehydrated weight of foods within the “sweets” category as catalogued by research dietitians. Sweets included desserts but also sports drinks and the nutritional shakes commonly recommended to transplant patients to maintain weight. A separate analysis using sugar as a nutrient, rather than food categories, gave a similar result: an additional 20.6% decrease per 100 grams. Sweets eaten without antibiotics showed no such effect to the microbiome; the damage appeared only when the two were combined.

A Hospital Pathogen and a Mouse Test

The sugar-antibiotic combination was not just tied to a decrease in general microbiome diversity, but specifically linked to growth of Enterococcus, a bacterial genus that can cause dangerous bloodstream infections in transplant patients and has been tied to graft-versus-host disease and death. In stool samples, E. faecium rose with sweets intake after antibiotic exposure.

The team further tested this in a mouse models. They found a single dose of the antibiotic biapenem produced a modest, temporary Enterococcus bloom. Adding sucrose to the animals’ diet increased the bloom by 16x on day 3 and 33x on day 6. Glucose and fructose, the two components of sucrose, also boosted the bloom, as did a commercial fruit smoothie. The effect held in mice fed a fiber-free diet, suggesting it isn’t simply about fiber displacement.

Without antibiotics, sucrose caused no change in the microbiome. In mice free of any other gut bacteria, sugar did not affect E. faecalis, indicating that the sugar-antibiotic disruption works in an existing microbial community.

Possible Link To Survival

The authors also looked at outcomes. Among patients with above-median sugar intake (relative to calories), each extra day of broad-spectrum antibiotics was associated with a 12% higher risk of death; in the below-median group the association was weaker and not statistically significant (1.07). A second analysis grouping patients by dietary pattern showed a similar split. The authors caution that lower overall food intake may partly explain the mortality signal.

As an observational study, there are some caveats. These were transplant patients who needed antibiotics in the first place, and their illnesses can impact what they eat. Any food eaten outside the hospital’s offerings was incompletely recorded. The authors call for independent cohorts and for prospective trials to test whether limiting sugar during antibiotic treatment improves clinical outcomes.

But despite these limitations, the researchers still flagged dietary simple sugars as amplifiers of antibiotic-induced microbiome disruption, and proposed that, “limiting sugar intake during antibiotic therapy may help mitigate microbiome injury.”