"The new work identifies dietary sugars as an amplifier of antibiotic-induced microbiome disruption, probably because the potentially harmful bacteria that survive the antibiotics are benefiting from the dietary sugars that they can use to expand," said William Jogia, a PhD student in Dr. Schluter's lab at NYU Langone's Institute for Systems Genetics and second author of the study.

Still, the mechanism remains an open question. "Whether sugar directly supports Enterococcus, weakens competing bacteria, or acts through another mechanism in patients remains to be seen," Jogia said.

Why study blood cancer patients?

The team chose people with blood cancers for practical reasons. These patients receive antibiotics frequently, and hospital staff can monitor their food intake closely. Researchers recorded what patients ate at every meal and collected microbiome samples daily.

That combination of detailed diet records and daily biological sampling made the project one of the largest and most detailed studies of its kind to date.

"The microbiome is emerging as an important factor in cancer care," said co-senior author Marcel van den Brink, MD, PhD, chief physician executive at City of Hope. "For patients undergoing intensive treatments such as bone marrow transplantation, the healthy diversity of the gut microbiome can have important implications for outcomes."

Patients with blood cancers who receive stem cell transplants often spend weeks in the hospital during chemotherapy and antibiotic treatment. In this setting, harmful species such as Enterococcus faecium can flourish once much of the surrounding microbial ecosystem has been, as the researchers put it, "destroyed."

How serious is the risk?

The stakes for these patients are high. "Especially in blood cancer patients, microbiome injury is associated with worse outcomes, including higher overall mortality and infections," said Jonathan Peled, co-senior author and associate director of the Center for Hematological Malignancies at Memorial Sloan Kettering.

For the general public, the implications are less certain. The study observed hospitalized cancer patients and mice, not healthy people taking a routine course of antibiotics. The results show an association, and the biological mechanism — sugar feeding surviving harmful bacteria — remains a hypothesis that needs direct confirmation.

Should you cut sugar while on antibiotics?

The practical takeaway, according to the researchers: temporarily reducing simple sugars during and after antibiotic treatment could be a simple, low-cost way to limit microbiome damage. But this is a suggestion grounded in observational data and animal experiments, not proven clinical advice.

"As we are learning how collateral damage of antibiotics to the microbiome are linked with long-term health problems, it's important to identify factors that limit these unintended health risks," said co-senior author Jonas Schluter, PhD, assistant professor in the Department of Microbiology at NYU Langone. "Our study, which used more than 9,000 recorded meals, suggests that modifying diet during and after antibiotics, specifically by reducing sweets intake, could help with that."

What comes next?

Clinical trials. Peled put it plainly: "An important next step will be to design clinical trials to test whether short-term dietary changes can improve clinical outcomes in patients."

Until those trials run, the evidence supports a reasonable but provisional conclusion — sugar appears to make antibiotic-induced gut disruption worse, and cutting back on sweets during treatment is a low-risk change that might help. How exactly sugar works in the body, and whether dietary changes measurably improve patient outcomes, remain questions for future research.