A common mistake with antibiotics: This is what sugar does to your intestines

A new study reveals that eating foods high in sugar in conjunction with antibiotic treatment may harm the gut microbiome, in ways that may make people more susceptible to serious infections. The study, published Wednesday in the journal Nature, took advantage of a natural experiment, looking at changes in gut bacteria in cancer patients who were hospitalized and received prolonged antibiotic treatment before undergoing stem cell transplants.

Because the patients ate exclusively hospital-prepared food, the researchers were able to precisely determine the types and amounts of foods they ate. This is rare in nutrition studies, which typically rely on what participants remember to eat hours or days before, a task that people often have difficulty performing accurately.

The gut microbiome consists of trillions of bacteria, viruses, and other microorganisms that colonize the human intestine. These organisms perform many functions, including aiding digestion, producing essential vitamins, and contributing to the functioning of the immune system.

Research has shown that the gut microbiome also communicates with the brain to produce neurotransmitters, such as serotonin, which plays an important role in sleep, mood, and stress levels. Studies have shown that diet greatly affects the number and diversity of bacteria that live in the intestines.

People who eat a variety of plant-based, high-fiber foods tend to have a greater diversity of gut microorganisms than those who eat highly processed foods. In general, the more diverse your gut microbiome is, the healthier it is.

Rich and diverse microbial communities in the intestine can prevent harmful microorganisms, known as opportunistic pathogens, from multiplying, taking over the intestinal environment and causing disease. Dr. Jonathan Bild, a physician researcher and one of the study's authors at Memorial Sloan Kettering Cancer Center, said, "One of the things that distinguishes this study from previous studies published in this field is that the gut microbiome of patients is severely disturbed, and their nutritional status is affected by cancer treatment."

The study was conducted by researchers from Memorial Sloan Kettering Cancer Center, NYU Langone Health in New York City, and City of Hope Cancer Center in Los Angeles. They investigated the changes that occurred in the normal intestinal bacteria after antibiotics and foods served in the hospital upset their balance and disorder.

Researchers have exploited this state of confusion to study the effect of certain types of foods on the composition of the gut microbiome. “We analyzed the data in different ways, and divided it into multiple categories to study it from different angles,” Bild said.

Researchers studied the relationship between major classes of macronutrients, such as fats, carbohydrates, and fiber, and different types of gut bacteria. They also studied the effect of specific foods, such as chicken, apples, and chocolate cake.

“What came up repeatedly was that the more sugar-rich foods we ate, regardless of the type of sugar, and especially added sugars that had more harmful effects, they seemed to interact with antibiotics in a way that would cause more damage to the gut microbiome,” Bild explained. The study was based on more than 1,000 stool samples collected from 173 patients who ate more than 9,400 meals prepared in the hospital.

Generally, the more intensive the antibiotic treatment, the greater the loss of diversity in the patient's microbiome. The researchers found that most types of foods were not associated with changes in the diversity of bacteria in the intestine.

But sweets, which researchers defined as sugars, sweetened foods and drinks, were different. The study showed that approximately every 100-gram increase in sweet consumption during antibiotic treatment was associated with a 24% reduction in the diversity of the patient's microbiome as measured in the stool sample.

A decrease in the diversity of gut bacteria has been linked to an increase in the numbers of some harmful organisms, such as Enterococcus faecium. Enterococcus bacteria are opportunistic organisms; They live in the intestines without causing harm, and are kept under control thanks to other types of bacteria that compete with them.

But when this balance is disturbed, such as when antibiotics are used that kill off other bacteria, these bacteria can begin to multiply excessively. In some cases, it may cross the intestinal wall and reach the bloodstream, where it can cause sepsis.

“In cases of bone marrow transplantation specifically, we have found that enterococcal bacteria can increase the severity of some complications of the transplantation, including what is known as graft-versus-host disease,” Bild noted. Graft-versus-host disease occurs when donated stem cells recognize the recipient's body as a foreign body and begin attacking their healthy tissue.

The team also tested whether it could induce the same changes in the gut microbiome that it observed in cancer patients, but in mice. He gave the mice a single injection of a broad-spectrum antibiotic, and noticed a slight increase in the numbers of Enterococcus bacteria.

But when the researchers added sugar to the mice's diet after giving them the antibiotic, the numbers of these bacteria increased 16-fold by the third day, and 33-fold by the sixth day. This increase may have real-world consequences as well.

Overall, patients with higher than average sugar intake were about 12% more likely to die after transplant than those with lower intake. This was a small, but statistically significant, increase.

"There is a limited change in the risk level," Bild said. Increased numbers of Enterococcus bacteria continued for about eight days after antibiotic treatment.

“It's a really remarkable study,” said Dr. Anthony Marisso, a professor of virology and microbiology at Baylor College of Medicine in Houston, who was not involved in the study. “These findings are important for patients undergoing transplantation, because what hospitals fear most is that they will become infected while receiving medical care,” Marisso added.

“This makes me wonder if we should change the diet in hospitals.” He pointed out that the next question is whether the results of the study also apply to people who take antibiotics outside the hospital, as can a diet high in sugar while taking antibiotics, for example to treat an ear infection, increase the risk of developing another infection later?

Bild said the study raises important questions, but it is not a randomized controlled clinical trial, as its researchers could not test different diets to see which might be more protective for people taking antibiotics. He added that because avoiding excessive sugar intake is generally a good idea, it makes sense to limit its consumption during antibiotic treatment.