Sugar May Worsen Antibiotic Damage to Gut Bacteria, Large Study Finds

A sweeping clinical study from City of Hope has uncovered a surprisingly simple dietary factor that appears to amplify one of modern medicine’s most common collateral damages: the disruption of the gut microbiome caused by antibiotics. Researchers analyzing thousands of meticulously documented hospital meals and more than a thousand stool samples found that patients who consumed more sugary foods while taking antibiotics were significantly more likely to lose the bacterial diversity that keeps the gut, and the immune system, functioning well. The findings, published in Nature, suggest that what patients eat during antibiotic treatment may matter just as much as which antibiotics they receive.

The research focused on one of the most medically vulnerable populations in oncology: patients with blood cancers undergoing allogeneic hematopoietic cell transplantation. In this intensive procedure, patients receive high-dose chemotherapy, sometimes combined with radiation, to destroy their immune systems before donor stem cells are introduced to rebuild them. These individuals spend weeks in the hospital and are routinely given antibiotics to prevent and treat infections during the period when their defenses are essentially wiped out. Eighty percent of the patients in the study received at least one broad-spectrum antibiotic, the class of drugs that exerts the strongest impact on the microbiome because it targets many types of bacteria at once, obliterating beneficial organisms along with dangerous ones.

Antibiotics are, of course, lifesaving tools, but their broad activity comes at a cost. By indiscriminately killing bacteria, they can hollow out the gut’s ecological diversity, creating space for opportunistic pathogens to flourish. Microbiome diversity is widely regarded as a key indicator of gut health, and its loss has previously been linked with poorer clinical outcomes in patients with cancer. Preserving that diversity, the new study suggests, may be within patients’ control through something as ordinary as their meal choices.

What sets this investigation apart from most nutrition research is the extraordinary granularity of its dietary data. Over five years, the research team tracked 9,419 meals eaten by 173 hospitalized patients. Every time a patient ordered a meal from the hospital kitchen, the tray arrived with a questionnaire asking them to record how much of each item they ate and drank. By combining these real-time records with the kitchen’s nutritional information, the scientists catalogued more than 40,000 individual food items. For each patient, the team followed between eight and 128 meals across a window stretching from 12 days before transplantation to 49 days after. In parallel, they profiled microbiome diversity in more than 1,000 stool samples from 158 patients.

Marcel van den Brink, M.D., Ph.D., co-senior author of the study and president of City of Hope Los Angeles and City of Hope chief physician executive, emphasized how unusual this dataset is. Unlike past nutrition studies that depend on patients’ recollections of what they ate or on other imprecise surveys, his team worked with meticulous dietary records collected in real time, a level of detail that allowed them to detect patterns that would otherwise be impossible to see. Van den Brink, a globally recognized leader in microbiome research, cell transplantation and cancer immunotherapy, collaborated with Jonathan Peled, M.D., Ph.D., of Memorial Sloan Kettering Cancer Center and Jonas Schluter, Ph.D., of NYU’s Grossman School of Medicine.

Armed with this data, the researchers deployed a battery of advanced statistical models to search for dietary patterns associated with injury to the gut microbiome. The signal that emerged was strikingly consistent. No matter how the team analyzed the data, the same result kept appearing: patients who consumed more sweets while taking antibiotics were more likely to experience a loss of microbiome diversity as aggressive microbes crowded out other strains of bacteria. One organism in particular stood out, Enterococcus, a bacterium whose domination of the gut is associated with a higher risk of bloodstream infections, graft-versus-host disease and other life-threatening complications in transplant patients.

The magnitude of the effect was substantial. The combination of high-sugar foods and broad-spectrum antibiotics appeared to multiply the damage to the microbiome, producing a 24 percent drop in bacterial diversity for every 100-gram increase in sweets consumed, an amount of sugar roughly equivalent to a large milkshake. In other words, the dietary factor did not merely add to antibiotic-induced injury; it appeared to interact with it, deepening the ecological collapse that broad-spectrum drugs alone can trigger.

To test whether the association reflected a genuine biological mechanism rather than a statistical coincidence, the researchers turned to animal models. They gave broad-spectrum antibiotics to healthy mice and fed the animals a variety of diets. Mice eating a high-sucrose diet rapidly developed an overgrowth of Enterococcus in their guts, mirroring the pattern seen in the hospitalized patients. Critically, mice that ate the high-sugar diet without receiving antibiotics maintained normal bacterial diversity, indicating that sugar alone was not the culprit; rather, it was the combination of sugar and antibiotics that proved destructive. Van den Brink noted that the convergence of animal studies with the patient data provides a compelling rationale for future clinical trials to evaluate whether reducing sugar intake during antibiotic use would protect the microbiome.

The implications extend well beyond the transplant ward. The microbiome is increasingly recognized as an important factor in cancer care, influencing how patients respond to therapy and how they recover from it, and the better clinicians understand what supports or disrupts it, the more opportunities they have to reduce treatment side effects. For hospitalized cancer patients, diet represents one of the most practical levers hospitals can pull to support recovery. Van den Brink pointed out an uncomfortable irony in current clinical practice: many of the foods and drinks that hospitals encourage patients to consume, including nutritional shakes, smoothies and sports drinks, are high in sugar, something he said will need to be re-evaluated when prescribing antibiotics.

The study also reframes the concept of antibiotic stewardship. Traditionally, stewardship has focused on limiting antibiotic use to prevent the emergence of resistance, but the new findings suggest it should also encompass how different antibiotics affect the microbiome, since some disrupt beneficial gut bacteria far more than others. Van den Brink encourages patients to ask their healthcare teams to ensure that antibiotics are thoughtfully chosen from equally effective treatment options for controlling infections. As for whether people on antibiotics should simply cut out sugar, he counsels a measured approach. It is premature, he said, to recommend that everyone taking antibiotics avoid sugar, but he also observed that there is no strong evidence that probiotics help preserve or restore microbiome diversity, even though many people take them anyway. Limiting sugar, by contrast, carries no known harm and is an easy thing to try. The work was supported by the National Cancer Institute, the National Heart, Lung and Blood Institute, and the Susan and Peter Solomon Microbiome, Nutrition and Cancer Program at Memorial Sloan Kettering Cancer Center, and it reinforces a growing movement in medicine to treat food not merely as fuel but as an active component of therapeutic care.

Subject of Research: The interaction between dietary sugar and antibiotics in disrupting gut microbiome diversity in cancer patients undergoing stem cell transplantation

Article Title: Study suggests skipping sweets during antibiotic treatment may help protect the gut microbiome

Article References: Study suggests skipping sweets during antibiotic treatment may help protect the gut microbiome. (n.d.). Original publication

Image Credits: AI Generated

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Keywords: gut microbiome, antibiotics, sugar, stem cell transplant, microbiome diversity, Enterococcus, cancer care, nutrition, food as medicine, City of Hope, Nature, antibiotic stewardship