A major study reveals that consuming sugar while on antibiotics can sharply worsen gut microbiome loss in cancer patients, raising their risk of life-threatening complications. The findings challenge current hospital nutrition practices and highlight a critical, modifiable risk factor.
Hospital food can do more harm than good for cancer patients on antibiotics. That’s the blunt message from a new Nature study. The research shows that eating sugar while taking antibiotics speeds up the loss of gut bacteria diversity. This loss is tied directly to higher death rates after bone marrow transplants.
The study followed 173 people with blood cancers. They were treated at Memorial Sloan Kettering Cancer Center, New York University, and other US hospitals. All got at least one antibiotic. Four out of five received broad-spectrum drugs that kill both good and bad bacteria. City of Hope and American Heart Association News both confirmed these findings. This is one of the largest and most detailed looks at how diet and antibiotics together affect the gut microbiome in cancer patients.
The study profiled stool samples from 158 patients, making it one of the most comprehensive datasets linking real-time nutrition and microbiome changes in cancer care.
Researchers tracked 9,419 meals and tested over a thousand stool samples. The pattern was clear. Patients who ate more sugary foods while on antibiotics lost more gut bacteria. Marcel van den Brink, co-author and chief medical officer at City of Hope, explained: "Patients who consumed more sweets while taking antibiotics were more likely to experience a loss of microbiome diversity, as aggressive microbes displaced and dominated other bacterial strains."
The risk was highest for those eating the most sugar. Each extra day on antibiotics raised the danger. The numbers are stark. Eating 100 grams more sweet foods—about a large milkshake—two days before a stool test led to a 24% bigger drop in gut bacteria diversity than antibiotics alone. New Scientist reported that this effect was seen across the whole group. The data was statistically solid.
One bug, Enterococcus faecium, took over when other bacteria vanished. Its overgrowth led to more bloodstream infections, graft-versus-host disease, and other serious problems in transplant patients. Animal tests backed this up. Healthy mice on antibiotics saw a small rise in enterococci. But when sugar was added, the bacteria multiplied up to 33 times in six days. Glucose, fructose, and even fruit purees had the same effect. But only if antibiotics had already wiped out the competition.
Earlier reviews in transplantation medicine have shown that reduced gut microbiota diversity is associated with worse outcomes, including higher infection rates and mortality. The new research adds the dietary factor—specifically sugar intake during antibiotic therapy—as a key modifiable risk for microbiome damage.
These results put hospital nutrition under the spotlight. Many patients are told to drink shakes, smoothies, and sports drinks. These are often packed with sugar. Van den Brink warns that this advice, though well-meaning, may actually make things worse for the gut.
Dr. Ildefonso Espigado, a hematologist at Hospital Universitario Virgen Macarena in Seville, was not part of the study. He expects these findings to change what cancer patients are told to eat. He points out that diet is something patients can control. Old "low-germ" diets based on boiled foods never had strong evidence behind them. Now, the focus may shift to cutting sugar during antibiotic treatment.
The study’s authors stress that this isn’t just about cancer. Antibiotics create gaps in the gut for anyone. Sugar feeds the wrong bacteria. The same thing happened in healthy mice. Cutting sugar during antibiotics could help protect the gut microbiome in healthy people too.
Gut health matters in cancer care. This research exposes a blind spot in hospital routines. The fix is simple. Limit sugar when antibiotics are prescribed. It could save lives. For hospitals and patients, the message is clear: what you eat during treatment is not just about comfort. It’s about survival.
