Gut bacteria is linked to weight gain following chemotherapy treatment for breast cancer, according to a study published in BMC Medicine.

Approximately 30% of patients with breast cancer who receive chemotherapy treatments gain weight; however, why this occurs in some women but not others is unclear. Chemotherapy has also been linked to conditions beyond weight gain, such as glucose intolerance, prediabetes, and risk of high blood pressure. Although this is well-documented, the underlying process behind it has yet to be identified, according to the researchers. 

The study involved 33 women who were about to begin chemotherapy to treat breast cancer and gynecological cancer. The women were weighed once before treatment and once approximately 5 weeks after treatment began. A stool sample was also collected prior to treatment in order to genetically character the microbiome of each participant, according to the study. 

Of the 33 participants, 9 gained a statistically significant amount of weight (3% or more) after treatment. The microbiome of these women had a smaller diversity of gut bacteria and different strains compared with the women who did not experience weight gain, according to the study. 

The composition of a patient’s intestinal bacteria may be able to predict whether they will gain weight as a result of chemotherapy, according to the study. When the gut microbiota of women who gained weight were transferred to germ-free mice, the mice developed glucose intolerance and signs of chronic inflammatory conditions were detected in the blood. This means that bacteria may be partially responsible for metabolic changes that lead to weight gain post chemotherapy treatment, according to the study. 

"We have shown for the first time that the pre-treatment microbiome of patients that gained weight following chemotherapy is different than the microbiome of patients that did not gain weight, and that fecal transplantation from patients that gained weight results in glucose intolerance, adverse lipid changes and inflammatory changes in germ-free mice,” Omry Koren, PhD, an expert in gastrointestinal bacteria, said in the press release. 

A follow-up study is currently underway in a larger patient population. Investigators are examining the microbiome of women at the end of chemotherapy in order to understand the effect it has on bacterial composition.

Reference:
Gut bacteria linked to weight gain following chemotherapy treatment for breast cancer [News Release] October 21, 2020; Ramat Gan, Israel. https://www.eurekalert.org/pub_releases/2020-10/bu-gbl102120.php. Accessed October 22, 2020.