Distinction of meal quality and interaction with the gut microbiota by breath volatilome analysis in humans.

Diet strongly influences the composition and metabolic activity of the gut microbiota, which in turn impacts host physiology and health. The metabolites produced by gut microbes include volatile compounds detectable in exhaled breath, which offers a window to investigate microbial-host interactions. The aim of this study was to explore the influence of balanced and unbalanced meals on exhaled breath composition, while using lactulose as a standardized fermentable substrate to probe microbial fermentation, and whether these changes are associated with gut microbiota composition. Twenty healthy volunteers (10 women/10 men; 22 ± 2 y) participated in three test days, each separated by a minimum 7-d washout period: test day 1 consisted in an acute lactulose intake and test days 2 and 3 were crossover test days with either balanced or unbalanced breakfasts and lunches. Fecal samples were collected before each test day for gut microbiota analysis via sequencing of the 16S RNA gene (V5-V6 region). Breath samples were collected at multiple time points during the test days and analyzed by selected-ion flow-tube mass spectrometry (SIFT-MS). Gut microbiota composition remained stable across test days. Exhaled breath responses followed three patterns: (i) compounds with a postprandial decline (hydrogen sulfide, lactic acid, heptanal, 2,3-butanedione, propanoic acid, and valeric acid), (ii) compounds showing meal-dependent increases, that might either reflect food composition (limonene, 1-phenylethanol/2-phenylethanol), microbial activity in the upper gastrointestinal tract (butyric acid/3-hydroxybutanone, ethanol), or microbial activity in the lower gastrointestinal tract (acetic acid, methanol), and (iii) compounds remaining stable over time with only minor variations. Exhaled acetic acid was negatively correlated with fecal Akkermansia, Anaerobutyricum, Blautia, Flavonifractor, Gordonibacter, Streptococcus, and Turicibacter, while exhaled methanol was positively associated with fecal Blautia and Gordonibacter. Our data support the interest of breath volatilome analysis as a non-invasive approach to monitor nutritional intake, food quality and nutrition-microbiota interactions in humans. Trial registration: Clinical Trial NCT05949411.