Credit: City of Hope
Study: Eating Sugar While on Antibiotics May Help a Dangerous Gut Germ Thrive
In A Nutshell
- In mice, sugar plus an antibiotic made a harmful gut germ bloom up to 33 times larger than the antibiotic alone.
- In 173 transplant patients, sweets paired with strong antibiotics were tied to a bigger drop in gut bacteria variety.
- Among higher-sugar patients, each extra antibiotic day was linked to a 12% higher risk of death, which does not prove cause.
- Researchers call for trials testing whether short-term sugar avoidance during antibiotic treatment improves outcomes.
In mice given an antibiotic, adding sugar to the diet made a dangerous gut germ called Enterococcus bloom up to 33 times larger than the antibiotic did alone. Hospital records from cancer patients showed a similar pattern in people. Those who ate more sweets while on strong antibiotics ended up with a thinner, less varied mix of gut bacteria.
Findings published in Nature came from 9,419 hospital meals eaten by 173 patients receiving transplants of blood-forming cells, a grueling treatment for blood cancers. Strong antibiotics here means broad-spectrum drugs that kill many kinds of bacteria at once. Enterococcus, a germ behind dangerous, drug-resistant bloodstream infections, also grew more in these patients, but only when sweets and those drugs overlapped.
Patients often have trouble eating during treatment, so sugar-rich nutrition shakes are commonly recommended to keep calories up. That made the pattern a real surprise to the researchers themselves.
Sugar With Antibiotics Was Tied to an Extra 24% Drop in Gut Bacteria Variety per 100 Grams of Sweets
Researchers at Memorial Sloan Kettering Cancer Center in New York studied adult transplant patients treated there between 2017 and 2022. Treatment means weeks in the hospital, heavy chemotherapy, and appetite-wrecking nausea and mouth sores. Patients marked on each meal tray how much of every item they ate, from none to all, and the hospital kitchen’s computer system converted those marks into grams. Researchers also collected 1,009 stool samples from 158 of the patients to track gut bacteria.
All 173 patients received antibiotics, and 138 (80%) were switched to broad-spectrum ones after a fever or another sign of infection. Using a statistical model, the team compared each stool sample with the food eaten over the previous two days, while accounting for chemotherapy intensity, tube or IV feeding, and other factors. Sweets alone showed no link to gut bacteria diversity, a measure of how many types of bacteria live in the gut and how evenly balanced they are. Gut bacteria help train the immune system and crowd out harmful germs, and earlier work from the same group tied low diversity to higher death rates in transplant patients.
During broad-spectrum antibiotic use, though, every additional 100 grams of foods in the researchers’ sweets-and-sugary-drinks category, measured after removing their water content, predicted an extra 24% drop in diversity. A separate analysis based on the amount of sugar itself found a similar pattern.
Several stress tests left the result intact: leaving out patients fed by tube or IV, leaving out samples taken during treatment for confirmed infections, and accounting for cancer type and other health problems. Nutritional shakes, sports drinks, and added sugars were among the main contributors.
Sugar Added to Antibiotics Fueled Up to 33-Fold More Enterococcus in Mice
To test whether sugar was causing the change or just tagging along, researchers turned to mice. A single antibiotic injection triggered a bloom of Enterococcus that peaked on day 3 and largely faded by day 6. Adding sucrose, or table sugar, to the animals’ food made that bloom 16.3 times larger on day 3 and 33.4 times larger on day 6 than in mice given the antibiotic alone. Mice given sugar without the antibiotic showed no change in Enterococcus.
Follow-up experiments tested other explanations. Sugar did not push out fiber-rich chow, since the mice ate about the same amount, and sugar still prolonged the bloom in mice fed a fiber-free diet. When glucose and fructose, the two simple sugars that make up table sugar, were tested separately, both increased the bloom early in the experiment. In mice raised with no gut bacteria except Enterococcus, sugar made no measurable difference to the germ’s growth, hinting that the boost depends on a gut already disrupted by antibiotics.
Each Extra Antibiotic Day Carried 12% Higher Death Risk Among Higher-Sugar Patients
Survival was the next question. Patients were split into two groups: those who got a bigger share of their food from sugar, and those who got less. In the higher-sugar group, each added day of broad-spectrum antibiotics was linked to a 12% higher risk of death. In the lower-sugar group, the link was a smaller 7% per day that could be explained by chance, so the gap between the two groups is modest.
These numbers describe an association, not proof that sugar affected survival. Broad-spectrum antibiotics usually begin when a patient has a fever or other signs of infection, so sicker patients, who may eat differently, could explain part of the pattern. The authors also note that lower food intake might account for some of the added risk. Checks for illness severity left the diversity finding intact, but this study only watched patients at a single hospital and never assigned diets.
Mice showed that sugar plus an antibiotic can magnify a dangerous germ, and transplant patients showed a matching tie between sweets, strong antibiotics, and a thinner gut bacteria mix. That falls short of proof that cutting sugar protects patients, and nothing here argues for dropping nutrition shakes entirely. The authors call for trials testing whether short-term sugar avoidance during antibiotic treatment improves outcomes, and patients on strong antibiotics can ask their care team about sweet drinks in the meantime.
Disclaimer: This article is for informational purposes only and is not medical advice. Patients should consult a qualified healthcare provider before changing diet or medication during treatment.
Paper Notes
Limitations
Human data in the study are observational, so it cannot show that sugar caused the changes in gut bacteria or survival. Broad-spectrum antibiotics were started based on clinical signs such as fever, so the severity of a patient’s underlying condition may partly explain the results, and the authors note that lower food intake could contribute to the added mortality risk. Nearly all patients received preventive fluoroquinolone antibiotics before escalating to broad-spectrum drugs, so the reported interaction may more precisely reflect diet during escalation to stronger antibiotics than exposure to any antibiotic. Patients were invited to report food from outside the hospital, but those records are incomplete, and changing symptoms such as nausea and appetite may add other unmeasured influences. The patients were adults treated at one cancer center for blood cancers, and the mouse experiments used female mice, so the findings may not apply to other groups. The authors state that prospective trials and independent patient groups are needed to test whether changing diet improves clinical outcomes.
Funding and Disclosures
Funding came from The Susan and Peter Solomon Microbiome, Nutrition and Cancer Program at Memorial Sloan Kettering Cancer Center, the National Heart, Lung, and Blood Institute, and the National Cancer Institute, including the Memorial Sloan Kettering Cancer Center Core Grant. NYU-based team members were funded by the National Institute of Allergy and Infectious Diseases, the National Cancer Institute, an award from the Gabrielle’s Angel Foundation, and a center grant to the NYU Perlmutter Cancer Center. Senior author Marcel van den Brink has also been supported by the National Institute on Aging, Starr Cancer Consortium, the Parker Institute for Cancer Immunotherapy, and other organizations listed in the paper. Several authors reported competing interests. Jonas Schluter reported filed intellectual property applications related to the microbiome, equity and an advisory role at Jona Health, and cofounding Postbiotics Plus Research. Jonathan Peled reported research funding, intellectual property fees, and travel reimbursement from Seres Therapeutics, consulting fees from multiple companies, and equity in Postbiotics Plus Research and Prodigy Biosciences. Memorial Sloan Kettering has financial interests in Seres Therapeutics. Other authors reported consulting, honoraria, stock, or equity ties to biotech and pharmaceutical companies, and one reported employment and equity at Savor Health. The remaining authors declared no competing interests. Full details appear in the original paper.
Publication Details
Title: Sugar-rich foods exacerbate antibiotic-induced microbiome disruption | Journal: Nature | DOI: https://doi.org/10.1038/s41586-026-11077-3 | Authors: Anqi Dai and Annamaria Ballweg (joint first authors), William Jogia, Madhumitha Rangesa, Peter A. Adintori, and colleagues from Memorial Sloan Kettering Cancer Center, NYU Langone Health, City of Hope National Medical Center, and other institutions. The work was jointly supervised by Marcel R. M. van den Brink, Jonas Schluter, and Jonathan U. Peled. | Accepted: 25 August 2026 | Published: 30 September 2026
