The research, which examined cancer patients receiving prolonged antibiotic treatment before stem cell transplants, found that higher consumption of sweets was associated with a greater loss of bacterial diversity in the gut and an increase in potentially harmful bacteria, particularly Enterococcus faecium.
The findings raise concerns about the possible role of diet in shaping patients’ response to antibiotic treatment, especially among people whose immune systems are weakened by cancer, intensive medical treatment or stem cell transplantation.
However, the researchers cautioned that the study established an association rather than a direct cause-and-effect relationship. They said further research would be needed to determine whether the findings also apply to people taking antibiotics outside hospital settings.
The researchers analysed more than 1,000 stool samples collected from 173 cancer patients who consumed over 9,400 hospital-prepared meals while undergoing treatment. The large volume of samples and meal records enabled the team to examine dietary patterns alongside changes in the patients’ gut microbiomes.
Lead author, Dr Jonathan Peled, said the study offered an opportunity to investigate how food consumption might influence gut bacteria in patients whose microbiomes were already being affected by antibiotics and cancer treatment.
The team examined the relationship between nutrients, including fats, carbohydrates and fibre, and the composition of gut bacteria. They also investigated the potential effects of individual foods, including chicken, apples and chocolate cake.
Among the different food categories assessed, sweets repeatedly emerged as a notable factor associated with greater disruption of the gut microbiome, with added sugars appearing particularly concerning.
Sugar consumption linked to loss of beneficial gut bacteria
According to the study, the intensity of antibiotic treatment was associated with a greater reduction in gut bacterial diversity. Although most food categories showed no significant relationship with changes in bacterial diversity, sweets — defined as sugars and sweetened foods and beverages — stood out.
The researchers found that for every additional 3.5 ounces of sweets consumed during antibiotic treatment, bacterial diversity in patients’ stool samples decreased by approximately 24 per cent.
Gut bacterial diversity is important because a broad community of microorganisms helps maintain intestinal health and can prevent potentially harmful bacteria from becoming dominant.
When antibiotics eliminate susceptible bacteria, they can disrupt this balance, reducing the competition that normally keeps certain microorganisms under control.
The study found that this disruption was associated with an increase in Enterococcus faecium, a bacterium that may live harmlessly in the gut but can cause serious infections when it multiplies excessively or enters parts of the body where it does not belong.
Under normal circumstances, beneficial and other resident microorganisms help limit the growth of potentially harmful bacteria. However, when antibiotics reduce these competing populations, Enterococcus can expand rapidly.
In some cases, the bacterium can cross the intestinal barrier and enter the bloodstream, potentially causing sepsis, a life-threatening condition in which the body's response to infection damages its own tissues and organs.
The findings suggest that dietary patterns may be one of several factors influencing the extent of microbiome disruption during antibiotic treatment, although the study did not establish that sugar consumption directly caused the bacterial changes.
Higher sugar intake associated with transplant mortality
The researchers also identified a potential link between sugar consumption and outcomes following stem cell transplantation.
Patients who consumed more sugar than the study average had approximately 12 per cent higher risk of dying after stem cell transplants than those who consumed less.
The finding is particularly relevant to bone marrow and stem cell transplant recipients, who may face severe complications because of their weakened immune systems and the effects of intensive treatment.
Peled noted that Enterococcus could aggravate complications such as graft-versus-host disease, a condition in which immune cells from a donor attack the recipient’s healthy tissues following transplantation.
The researchers also observed that the expansion of Enterococcus bacteria persisted for approximately eight days after antibiotic treatment, suggesting that disturbances in the gut microbiome may continue even after a course of antibiotics has ended.
Peled described the difference in mortality risk as a modest change in patients’ risk profiles, rather than evidence that sugary foods directly caused deaths.
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| A former patient at Kelina Hospital, Temilola Ogunyemi-Oke (second left); the President of Kelina Hospital, Dr. Celsus Undie; Chairman Board of Directors, Ifeanyi Anago and others during a press conference to mark the hospital’s one year anniversary of Robotic surgery held in Lagos. |
Other factors associated with patients’ underlying illnesses, treatments and overall health could also influence their gut bacteria and survival.
Researchers call for further investigation
Despite the limitations, Peled said reducing excessive sugar consumption during antibiotic treatment could be a reasonable precaution, given the established general health benefits of avoiding too much added sugar.
He emphasised, however, that the findings did not necessarily justify eliminating all sugary foods from patients’ diets.
Instead, the study raises the possibility that moderating the consumption of sweets and sweetened beverages during antibiotic treatment could help limit disruptions to the gut microbiome, although further research is required to determine whether dietary changes can meaningfully reduce infection risks.
The researchers also called for additional studies to establish whether the relationship observed among cancer patients receiving intensive hospital treatment applies to other groups, including people taking antibiotics for common infections.
For now, the findings highlight the importance of investigating diet as a potential factor in antibiotic-associated microbiome changes, particularly among patients who are already vulnerable to serious infections.
The study does not establish that eating sugar while taking antibiotics will inevitably lead to an infection or worsen a patient's outcome. Rather, it provides evidence of an association that researchers say warrants further investigation.
As scientists continue to explore the relationship between diet, gut bacteria and medical treatment, the findings underscore the need for more research into whether practical dietary adjustments could complement existing measures to protect vulnerable patients from potentially life-threatening complications.