Eating Sweets on Antibiotics May Wreck Your Gut Microbiome, Study Finds

If you've ever wondered whether what you eat during a course of antibiotics matters for your gut, a new study published in Nature points to sugar as a specific culprit, at least in one high-risk group of patients. Researchers tracked real-world eating habits and gut bacteria in hospitalized cancer patients undergoing a bone marrow transplant while on antibiotics, and found that the more sweets patients ate, the more their gut bacterial diversity collapsed. This article is based on published coverage of the study rather than the full peer-reviewed paper, which wasn't available for direct review, so some details below are necessarily limited to what that coverage reported.

Key takeaways:

• In hospitalized cancer patients on antibiotics, eating more sweets was linked to a sharp drop in gut bacterial diversity.
• The harmful bacterium Enterococcus overgrew under the combination of high sugar and antibiotics, a pairing tied to higher infection risk.
• Mouse experiments support the human finding: a high-sugar diet alone didn't hurt gut diversity, but combined with antibiotics it caused the same bacterial overgrowth.
• This is a narrow, high-risk patient population and an observational human finding; the full study wasn't available for this article, which relies on published coverage.

Sugar Intake Tracked Against Gut Diversity Loss During Antibiotic Treatment

Researchers at City of Hope found that for every 100-gram increase in sweets a patient consumed while on antibiotics, their gut bacterial diversity dropped by 24%, according to the published coverage of the study. The effect was described as particularly strong in patients on broad-spectrum antibiotics, which covered roughly 80% of the patients studied. Alongside the diversity loss, the bacterium Enterococcus, a species linked to bloodstream infections and graft-versus-host disease in transplant patients, proliferated under the combined high-sugar, antibiotic conditions.

Why This Matters for Patients on Antibiotics, Especially After a Transplant

The finding centers on people undergoing an allogeneic hematopoietic cell transplant (a stem cell transplant using a donor's cells, commonly used to treat blood cancers), a population already known to be vulnerable to gut microbiome disruption and graft-versus-host disease from the antibiotics these patients routinely receive during treatment. For this group, Enterococcus overgrowth is not a minor lab finding, it's connected to real complications including bloodstream infections. The coverage doesn't establish that the same sugar effect applies to someone taking a short course of antibiotics for, say, a sinus infection, but it adds specificity to a broader, already-documented pattern: broad-spectrum antibiotics reliably damage gut microbial diversity in transplant patients, and this work suggests diet may modulate how much damage occurs.

How Researchers Tracked Diet and Gut Bacteria Over Five Years

According to the coverage, the study followed patients over five years, analyzing 9,419 meals and more than 1,000 stool samples from 158 patients out of a tracked cohort of 173. Rather than relying on food-frequency questionnaires or recall, researchers combined meal questionnaires with hospital kitchen records to capture real-time data on more than 40,000 individual food items, an approach the coverage described as more precise than prior nutrition studies in this setting. Lead researcher Dr. Marcel van den Brink was quoted saying, "No matter how we analyzed the data, the same strong signal kept appearing," regarding sugar's association with microbiome disruption during antibiotic treatment.

What This Means if You're Facing a Course of Antibiotics

This isn't evidence that cutting sugar prevents antibiotic-related gut problems for the general public, the human data here comes from a narrow, high-risk hospitalized population, not healthy adults on a short antibiotic course. For patients in similar circumstances, cancer treatment involving stem cell transplant and extended antibiotic use, this is worth a conversation with the care team about diet during treatment, though the coverage doesn't describe any specific dietary intervention being tested or recommended. For everyone else, it's a reasonable, if unproven, nudge to think about sugar intake as one of several factors that might matter alongside antibiotics, not a basis for skipping medically necessary treatment or self-prescribing a diet change.

Why This Finding Still Needs the Full Study and More Data

Because the underlying peer-reviewed paper wasn't available for this article, the details here are limited to what the published coverage reported, and some specifics, such as statistical confidence intervals or whether the researchers controlled for other dietary and clinical factors, aren't available. The human portion of the finding is observational: patients who ate more sugar weren't randomly assigned to do so, which leaves open the possibility that illness severity, appetite changes, or other factors unmeasured here contributed to both sugar intake and diversity loss. The coverage reviewed for this article did not state whether the authors disclosed any conflicts of interest. The mouse experiments, where researchers could control diet and antibiotic exposure directly, support a causal role for the sugar-antibiotic combination, which strengthens the human finding without fully resolving it. That mouse result also lines up with separate research showing high-sugar diets can independently reduce gut microbial diversity in animal models, even outside the antibiotic context.

Next Steps: Confirming the Finding Beyond This Cohort

The published coverage doesn't describe a specific follow-up trial, but the combination of a large real-world human dataset and a controlled mouse model is the kind of pairing that typically motivates a prospective dietary intervention study, testing whether deliberately limiting sugar during antibiotic treatment actually preserves gut diversity or improves outcomes like infection rates. Until such a trial exists, this remains an association worth watching rather than a proven intervention.

Common Questions

Should I stop eating sugar while taking antibiotics? The study doesn't test or recommend a specific sugar limit; it found an association in hospitalized cancer transplant patients. There's no established guidance from this research for general antibiotic users.

What is Enterococcus and why does it matter? Enterococcus is a bacterium that can overgrow when gut diversity collapses; in transplant patients, this has been linked to bloodstream infections and graft-versus-host disease, a serious transplant complication.

Does this apply to a short course of antibiotics for something like a UTI? The human data comes specifically from hospitalized cancer patients on antibiotics during a stem cell transplant, not short-term outpatient antibiotic use, so it's not known whether the same relationship holds in that very different setting.

References

1. Anqi Dai, Annamaria Ballweg, William Jogia, et al. (2026). Sugar-rich foods exacerbate antibiotic-induced microbiome disruption. Nature. https://doi.org/10.1038/s41586-026-11077-3
2. Karen Madsen (2018). A High Sugar Diet Rapidly Enhances Susceptibility to Colitis Via Depletion of Luminal Short-Chain Fatty Acids. https://doi.org/10.2139/ssrn.3228218