Researchers analyzing hospital meal records from 173 cancer patients receiving stem cell transplants discovered that consuming sweet foods during antibiotic treatment is associated with a sharp drop in gut bacterial diversity and an increase in potentially harmful microbes, according to a cohort study published in Nature.
When adult patients at Memorial Sloan Kettering Cancer Center in New York were admitted for allogeneic hematopoietic cell transplantation between 2017 and 2022, they entered an unusual environment for dietary tracking. Hospital kitchen software generated a printout for every meal tray, on which participants recorded whether they consumed none, a quarter, half, three-quarters, or all of each item ordered. These records were collected three times weekly, vetting entries manually to maintain high-quality nutritional data during inpatient hospitalization.
That detailed log of more than 9,400 hospital meals and over 1,000 stool samples allowed investigators from Memorial Sloan Kettering Cancer Center, NYU Langone Medical Center, and City of Hope Comprehensive Cancer Center to examine how food interacts with gut health while patients take intensive medications. While most foods showed no clear link to shifts in the microbiome, sweet items stood out in the resulting analysis.
How Sweet Foods and Antibiotics Alter the Gut Microbiome
Intensive antibiotic treatments are known to deplete beneficial bacteria, often leading to digestive distress or leaving room for resilient organisms to multiply. The new findings indicate that consuming sugar and sweet foods during that vulnerability accelerates the imbalance. Statistical models estimated that every additional 3.5 ounces—roughly 99 grams—of sweets consumed during treatment corresponded with about a 24% greater decline in bacterial diversity within patient samples.
As diversity plummeted, certain microorganisms proliferated. Chief among them was Enterococcus faecium, a bacterium that can multiply rapidly when competing microbes vanish under the pressure of broad-spectrum drugs. For immunocompromised blood cancer patients, that overgrowth carries clinical consequences. Jonathan Peled, a physician-scientist at Memorial Sloan Kettering Cancer Center, noted that rising enterococcus levels in bone marrow transplant recipients can exacerbate graft-versus-host disease, a complication where donor cells attack the recipient’s healthy tissue.
To test whether sugar actively drove the bacterial shift, researchers turned to an animal model. Mice given a broad-spectrum antibiotic alongside a high-sugar diet experienced a dramatic surge in enterococcus populations. By the third day, their bacterial levels were 16 times higher than in mice that received antibiotics alone; by the sixth day, those levels reached 33 times higher according to experimental observations. Mice receiving sugar without antibiotics showed no comparable disruption, suggesting high-sugar intake primarily intensifies an imbalance already initiated by drugs.
The cohort analysis also tracked patient outcomes following their stem cell procedures. Investigators observed that among individuals who consumed more sugar than average during their inpatient stay, the post-transplant risk of death was roughly 12% higher than among those with lower sugar intake. However, study leaders cautioned that this correlation does not establish a direct cause-and-effect relationship between dietary sweets and mortality rates.
Because the investigation was an observational cohort study rather than a randomized clinical trial, researchers emphasize that it remains unknown whether these associations apply to healthy individuals taking short courses of antibiotics at home for common outpatient infections.
What Clinical Experts Recommend for Patients Taking Antibiotics
Medical guidance derived from the research stresses that patients undergoing intensive cancer treatment or stem cell transplantation should not drastically restrict their overall nutrition or stop taking prescribed nutritional supplements without consulting their medical team due to the critical need for calories and protein.
For the general public taking routine antibiotic prescriptions, complete elimination of sugar is unnecessary.
- Reduce consumption of sugary beverages and excessive sweets while completing an antibiotic course.
- Maintain balanced nutrition that includes vegetables, whole grains, and fiber to support residual gut flora without avoiding natural food sources like fresh fruit and milk.
- Consult a physician before using probiotics to manage antibiotic-related diarrhea, as live bacterial products can carry infection risks for immunocompromised individuals.
While the study demonstrates a clear link between heavy sugar consumption and diminished gut bacterial diversity during antibiotic therapy in an inpatient cancer cohort, researchers continue to study whether targeted dietary modifications can actively prevent opportunistic infections in broader patient populations.