Association Between Composition of the Gut Microbiota and Nutritional Status in Digestive Oncology

Nutritional status represents a crucial issue in the management of cancer patients, as between 40% and 60% of them suffer from malnutrition at the time of diagnosis. This condition worsens morbidity, increases treatment-related adverse effects, infections, and hospitalizations, and can lead to death in 10% to 20% of cases, independently of tumor progression. Anticancer treatments often exacerbate malnutrition due to their side effects, such as loss of appetite or taste alterations. Although international guidelines (ESPEN, ESMO, ASCO) recommend a multimodal nutritional intervention combining nutritional support and physical activity. The effectiveness of these approaches varies among patients. This variability can be explained by several factors, including individual differences in dietary intake response, metabolic status, and digestive tolerance to treatments. The intestinal and oral microbiota appear to be key cofactors in regulating these various parameters, influencing appetite, host metabolism, and intestinal absorption. Alterations in the microbiota-particularly a decrease in bacterial diversity and an increase in Candida albicans-have been associated with appetite loss and taste perception disorders, especially in patients with digestive cancers. Therefore, the intestinal microbiota constitutes a potential therapeutic and diagnostic target to improve nutritional strategies in oncology. Interventions targeting the microbiota (such as probiotic supplementation or fecal microbiota transplantation) have already demonstrated an impact on nutritional parameters in preclinical models of malnourished cancer-bearing mice; however, clinical data remain scarce and limited. The ONCONUTRIBIOTA-cohort study aims to characterize and investigate the oral and intestinal microbiota of patients initiating chemotherapy for digestive cancer, in relation to their nutritional status clinical characteristics and food preferences, in order to identify potential biomarkers or the