Sugar Consumption May Harm Cancer Patients on Antibiotics, Study Warns

Cancer patients undergoing intensive treatment who consume sugar while taking antibiotics may face life-threatening complications, according to a new study by researchers at City of Hope.

The study, published in a recent research paper, suggests that avoiding sugary foods during antibiotic treatment could protect the body's microbiome—the collection of beneficial bacteria essential for immune function and overall health.

Antibiotics, while crucial for fighting infections, can disrupt the delicate balance of the gut microbiome by killing both harmful and beneficial bacteria. This disruption can lead to side effects such as diarrhea, bloating, gas, and increased susceptibility to other infections. For cancer patients, maintaining microbiome diversity has been linked to better clinical outcomes.

Researchers tracked the dietary habits and microbiome diversity of 173 patients undergoing intensive treatment for blood cancer, 80 percent of whom received broad-spectrum antibiotics known to significantly impact the microbiome. The team analyzed over 9,400 meals and more than 1,000 stool samples.

"Unlike past nutrition studies that rely on patients’ memories of what they ate or other imprecise surveys, we had meticulous dietary records collected in real time," said co-senior author Dr. Marcel van den Brink, president of City of Hope Los Angeles and chief physician executive. "This enabled us to look for patterns that otherwise might be impossible to detect."

The analysis revealed a consistent pattern: patients who consumed more sweets while taking antibiotics experienced a greater loss of microbiome diversity. For every 100-gram increase in sweets—roughly the amount in a large milkshake—bacterial diversity declined by 24 percent. This decline allowed aggressive microbes to crowd out other bacterial strains.

One organism of particular concern that showed increased growth was Enterococcus. Overgrowth of this bacterium in the microbiome is associated with higher risks of bloodstream infections and life-threatening complications in patients undergoing transplants.

To further investigate, researchers fed mice a high-sucrose diet while they were on broad-spectrum antibiotics. This dietary intervention led to a rapid overgrowth of enterococcus in their guts, confirming the findings from the human study.

"The confirmation seen in the animal study provides a compelling rationale for future clinical trials evaluating sugar intake during antibiotic usage," Dr. van den Brink stated. The findings reinforce the idea that diet plays a significant role in patient recovery and offer a practical approach for hospitals to support patients undergoing certain treatments.

"The microbiome is emerging as an important factor in cancer care," he added. "The better we understand what supports and disrupts it, the more opportunities we have to reduce treatment side effects while improving how patients respond to and recover from therapy."