Co-senior author Marcel van den Brink, M.D., Ph.D., president of City of Hope Los Angeles and City of Hope chief physician executive. Credit: City of Hope
A new study from City of Hope suggests that cutting back on sugary foods during antibiotic treatment may help protect the gut microbiome, based on one of the most detailed nutrition datasets ever collected in a clinical setting.
The five-year study followed patients with blood cancer undergoing allogeneic hematopoietic cell transplant—an intensive treatment involving chemotherapy, sometimes paired with radiation, to wipe out the immune system before a stem cell transplant. The treatment leaves patients at especially high risk for severe microbiome disruption since all patients require antibiotics during their hospital stay to prevent or treat infections.
Published in Nature, the findings connect to the idea of “food as medicine” during cancer care and the ways diet can help us prevent and recover from illness. The research could lead to new treatment strategies for cancer patients and potentially others taking antibiotics.
An unprecedented dataset
Antibiotics are used to treat infections, but they also broadly destroy good bacteria in the gut, allowing the overgrowth of harmful microbes.
Every one of the 173 patients in the 5-year study took at least one antibiotic during their hospital stay, with 80% of them taking one or more broad-spectrum antibiotics.
The research team tracked 9,419 meals eaten by the hospitalized patients and profiled the microbiome diversity in stool samples from 158 patients, drawing on more than 1,000 samples total. Microbiome diversity is a key indicator of a healthy microbiome.
Each time a patient ordered a hospital meal, the tray came with a questionnaire asking them to record exactly how much of each item they ate or drank. That process allowed the team to log more than 40,000 individual food items—a level of dietary detail rarely achieved in nutrition research.
For each patient, the researchers tracked between eight and 128 meals across a window spanning 12 days before to 49 days after transplant.
“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 van den Brink. “This enabled us to look for patterns that otherwise might be impossible to detect.”
Using several statistical models to search for patterns linked to microbiome injury, the researchers found a consistent result.
“No matter how we analyzed the data, the same strong signal kept appearing,” van den Brink said. “The 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, which can dominate the gut microbiome and raise a transplant patient's risk of bloodstream infections, graft-versus-host disease and other serious complications. The combination of high-sugar foods and broad-spectrum antibiotics appeared to compound the damage, with a 24% drop in bacterial diversity for every 100-gram increase in sweets—the equivalent in sugar content to a large milkshake.
Mouse studies support human data
To test the connection further, the researchers gave broad-spectrum antibiotics to healthy mice fed a variety of diets. Mice on a high-sucrose diet quickly developed an overgrowth of Enterococcus, while mice fed the same high-sugar diet without antibiotics maintained normal bacterial diversity.
“The fact that animal studies support associations we found in patient data provides a compelling rationale for future clinical trials to evaluate whether reducing sugar intake during antibiotic use would protect the microbiome,” van den Brink said.
What the results mean
For cancer patients, the study results reinforce diet as a strong influence on the microbiome and as one of the most practical ways hospitals can support recovery during treatment.
“Many of the foods and drinks we encourage hospitalized patients to consume, like nutritional shakes, smoothies and sports drinks, are high in sugar content,” said van den Brink. “That’s something we’ll need to evaluate when prescribing antibiotics.”
The takeaway for physicians is that antibiotic stewardship matters beyond preventing antibiotic resistance.
“Antibiotic stewardship includes thinking about how different antibiotics affect the microbiome,” concluded van den Brink. “Our study demonstrates that some antibiotics disrupt beneficial gut bacteria more than others.”