Antibiotics Plus Sugar: A Double Hit to the Gut Microbiome
Many people know antibiotics can upset the stomach, but a new study reveals a detail that is easy to overlook: eating sugary foods while taking antibiotics may cause even greater damage to gut bacteria, potentially leaving people more vulnerable to dangerous infections.
The research, published Wednesday in the journal Nature, was led by scientists at Memorial Sloan Kettering Cancer Center, NYU's Langone Health in New York, and City of Hope Cancer Center in Los Angeles.
A Rare 'Natural Experiment': Hospital Food and Antibiotics
Nutrition studies typically rely on participants recalling what they ate, which people are notoriously bad at. This study took advantage of a unique setting: cancer patients who were hospitalized and treated with sustained antibiotics before stem cell transplants, and who ate only food prepared by the hospital. Researchers therefore knew exactly what and how much they ate.
The study analyzed more than 1,000 stool samples from 173 patients and data from over 9,400 hospital-prepared meals.
Key Finding: Sugar and Antibiotics 'Synergize' to Harm the Microbiome
"The theme that kept popping up over and over again was the more sugary foods you eat, no matter what type of sugar it is – with particularly noxious effects from added sugars – it seemed to really synergize with antibiotics in terms of damaging the microbiome," said study author Dr. Jonathan Peled, a physician scientist at Memorial Sloan Kettering.
- The more intense a patient's antibiotic regimen, the greater the loss of microbiome diversity.
- Most food types were not associated with changes in bacterial diversity, but sweets were a different story.
- For every 3.5-ounce increase in sweets consumption during antibiotic treatment, microbiome diversity in stool samples dropped by about 24%.
Why Do Bad Bacteria Take Over?
The decrease in diversity was tied to expansions of certain bad actors, such as Enterococcus faecium. This bacterium normally hangs around harmlessly in the gut, kept in check by other bacteria. But when antibiotics wipe out those competitors, it can overgrow, slip through the gut wall, and enter the bloodstream, where it can cause sepsis.
In bone marrow transplant patients specifically, Peled said, Enterococcus can worsen complications such as graft versus host disease.
Mouse Study Confirms: Sugar Fuels a 33-Fold Increase
The team also tested whether they could recreate these microbiome shifts in mice. A single injection of a broad-spectrum antibiotic caused a small increase in Enterococcus. But when mice were also fed added sugar after the antibiotic shot, Enterococci increased 16-fold by day three and 33-fold by day six.
Among patients, those who ate more sugar than average had about a 12% higher risk of dying after their transplants compared with those who consumed less. Peled called it "a modest change in their risk profile," but it was statistically significant.
What Experts Say
Dr. Anthony Maresso, professor of virology and microbiology at Baylor College of Medicine in Houston, who was not involved in the research, called it "a pretty neat study" and said, "I suspect it's going to make some waves." He added that it raises the question of whether hospitals should change patient diets.
The next question is whether this has significance for people who take antibiotics outside a hospital setting – for example, whether a high-sugar diet during antibiotics for an ear infection sets you up for other infections down the road.
Practical Advice: Should You Avoid Sugar During Antibiotics?
Peled stressed that this is not a randomized, controlled clinical trial, so it cannot prove cause and effect. But since avoiding too much sugar is generally a good idea, limiting sugar during antibiotic treatment is not unreasonable.
"What our study suggests might work is not to avoid sugar or sugary foods during your entire time, but specifically when you're on antibiotics," Peled said.
Everyday Health Tips
- During antibiotic treatment, try to limit desserts, sugary drinks, and added-sugar snacks.
- Eat more fiber-rich, plant-based foods to help maintain gut microbiome diversity.
- If you want to track diet, medication, and body metrics over time, consider logging them.
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