Delzenne, Nathalie M.Debier, CathyRombaux, MarieMarieRombaux2025-05-142025-05-142025-05-142024https://hdl.handle.net/2078.2/41604The gut microbiota, a complex community of microorganisms residing in the human gastrointestinal tract, plays a crucial role in regulating host physiology, including metabolism, immune defense, and behavior. Recent research highlights the connection between microbiota composition and various health conditions such as metabolic disorders and gastrointestinal diseases. This master’s thesis was conducted at UCLouvain's Metabolism and Nutrition laboratory, as part of the Microboost-1 project. It investigates the triangular interaction between gut microbiota, nutrition, and host health, focusing on hydrogen and methane production using the Lactotest and using some of the results obtained by Selected-Ion Flow-Tube Mass Spectrometry (SIFT-MS). Healthy volunteers were subjected to dietary interventions, and exhaled breath volatile metabolites were analyzed to assess microbial activity. The impact of eating a balanced and unbalanced meal was tested on 20 volunteers to evaluate the potential effect of food quality on exhaled gases and metabolites. Moreover, the influence of lipid or protein loading on the production of gases and volatile organic compounds in breath was tested on 5 volunteers as part of a preliminary test. Furthermore, the master’s thesis introduces a protocol to confirm the identity of key metabolites in breath that are produced by the gut microbiota focusing on three compounds of interest (pentane, acetic acid and butyric acid), by implementing a spiking process, first in an inert gas (helium), and second in breath samples. The results revealed the importance of a harmonized protocol for correctly interpreting exhaled gas data, with particular attention to test duration and prior dietary control. All the volunteers who took part in the lactulose test were hydrogen producers and only one of them was also a methane producer. This indicates that some individuals are co-producers of methane and hydrogen, suggesting a complex gut microbial ecosystem. In addition, analysis revealed simultaneously elevated levels of hydrogen and hydrogen sulfide in the breath of some participants. Lactulose ingestion mainly increased flatulence and rumbling, probably due to fermentation in the intestine, while other gastrointestinal symptoms were less affected, and a negative correlation was found between methane exhaled in breath and gastrointestinal reflux and nausea. The test days comparing balanced and unbalanced meals revealed no significant difference in hydrogen release, but the unbalanced meal appeared to increase methane production, particularly 5 hours after breakfast. The test on 5 volunteers revealed an increase in acetic acid concentrations due to the ingestion of a fiber-rich meal the day before and methanol levels peaking 5 hours after fruit ingestion. Finally, the spiking experiment highlighted the need to refine the experimental methods to improve the precision of the measurements and better understand the interactions between the microbiota, nutrition and intestinal health. It enabled to propose concrete improvements to the current SIFT-MS method. This research contributed to develop personalized nutritional strategies to optimize gut health. The findings underscore the potential of breath analysis as a non-invasive tool for monitoring gut microbiota activity and suggest further exploration into the interactions between diet, microbiota, and host health, extending studies to more diverse populations in terms of age and health conditions.Gut microbiotaBreathVolatolomeLactotestGut transittext::thesis::master thesisthesis:46785