Sugar intake during antibiotic use may disrupt gut microbes

Eating sugary foods while taking antibiotics may disrupt the gut microbiome in ways that leave people more exposed to serious infections, according to a new study.

The research, published in the journal Nature, used a natural experiment involving cancer patients who were hospitalized, given prolonged antibiotic treatment and later received stem cell transplants. Because their meals were prepared by the hospital, scientists knew exactly what they ate and how much, offering an unusually precise look at diet in nutrition research.

The gut microbiome is made up of trillions of bacteria, viruses and other microbes living in the intestines. These organisms help digest food, produce essential vitamins and contribute to immune function. Research also suggests the microbiome communicates with the brain and helps influence neurotransmitters such as serotonin, which affect sleep, mood and stress.

Diet plays a major role in shaping the number and variety of bacteria in the gut. People who eat diverse, plant-heavy, fiber-rich diets generally have greater microbial diversity than those who rely more on highly processed foods. In broad terms, a more diverse microbiome is considered healthier because it can help keep harmful organisms, known as pathobionts, from gaining an advantage.

“One of the things that differentiates this study from other ones that have been previously published is that the patients are having their microbiome pummeled, and they’re also having their nutritional state disrupted by the cancer treatment,” said study author Dr. Jonathan Peled, a physician scientist at Memorial Sloan Kettering.

The study, led by researchers at Memorial Sloan Kettering Cancer Center, NYU Langone Health in New York and City of Hope Cancer Center in Los Angeles, examined how antibiotics and hospital food destabilized normal gut flora. That disruption allowed the team to study how different foods affected the microbiome’s composition.

“We sliced and diced the data in different ways,” Peled said.

The researchers examined how broad nutrient groups such as fat, carbohydrates and fiber related to different gut bacteria. They also looked at specific foods, including chicken, apples and chocolate cake.

“And 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 that really seemed to synergize with antibiotics in terms of damaging the microbiome,” Peled said.

The analysis included more than 1,000 stool samples from 173 patients who ate more than 9,400 hospital-prepared meals.

Overall, stronger antibiotic treatment was associated with a greater loss of microbial diversity in the gut.

Most food categories were not linked to changes in bacterial diversity, but sweets — defined by the researchers as sugars and sweetened foods and drinks — were different. For every 3.5-ounce increase in sweets consumed during antibiotic treatment, stool-based microbiome diversity dropped by about 24%, the study found.

That decline in diversity was associated with growth in certain potentially harmful bacteria, including Enterococcus faecium.

Enterococcus is an opportunistic microbe that can live harmlessly in the gut and is usually held in check by other bacteria. When that balance is disrupted, such as after antibiotics remove competing microbes, it can overgrow. In some cases, it can pass through the gut wall and enter the bloodstream, where it may cause sepsis.

“In bone marrow transplant specifically, we found that Enterococcus can make certain complications of transplant worse, something called graft versus host disease,” Peled said.

In graft versus host disease, donated stem cells identify the recipient’s body as foreign and attack healthy tissue.

The researchers also tested whether they could reproduce the microbiome changes seen in the cancer patients in mice. After a single dose of a broad-spectrum antibiotic, the mice showed a small rise in Enterococcus bacteria. When they were also fed added sugar, Enterococci levels rose 16-fold by day three and 33-fold by day six.

The findings may have meaningful clinical implications. Patients who ate more sugar than average had about a 12% higher risk of dying after their transplants than those who consumed less, a modest but significant increase in risk.

“It’s a modest change in their risk profile,” Peled said.

The Enterococcus expansion lasted for about eight days after antibiotic treatment.

“It’s a pretty neat study,” said Dr. Anthony Maresso, a professor of virology and microbiology at Baylor College of Medicine in Houston, who was not involved in the research. “I suspect it’s going to make some waves,” he added.

“This has significance for these transplant recipients because that’s the number one thing hospitals are worried about is that they’re going to get infections in the clinical care setting,” Maresso said. “Makes me wonder about whether we should change the diet of hospitals.”

He said the next question is whether the findings matter for people taking antibiotics outside a hospital. For example, does a high-sugar diet during antibiotic treatment for an ear infection increase the risk of later infections?

Peled said the study is intriguing, but it was not a randomized controlled trial designed to test different diets and determine which would be most protective for people taking antibiotics.

Still, because reducing sugar intake is generally a good idea, he said it may be reasonable to limit sugar during antibiotic treatment.

“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.