The gut microbiome plays an important role in human health and influences the development of chronic diseases ranging from metabolic disease to gastrointestinal disorders and colorectal cancer. Of increasing prevalence in Western societies, these conditions carry a high burden of care. Dietary patterns and environmental factors have a profound effect on shaping gut microbiota in real time. Diverse populations of intestinal bacteria mediate their beneficial effects through the fermentation of dietary fiber to produce short-chain fatty acids, endogenous signals with important roles in lipid homeostasis and reducing inflammation. Recent progress shows that an individual’s starting microbial profile is a key determinant in predicting their response to intervention with live probiotics. The gut microbiota is complex and challenging to characterize. Enterotypes have been proposed using metrics such as alpha species diversity, the ratio of Firmicutes to Bacteroidetes phyla, and the relative abundance of beneficial genera (e.g., Bifidobacterium, Akkermansia) versus facultative anaerobes (E. coli), pro-inflammatory Ruminococcus, or nonbacterial microbes. Microbiota composition and relative populations of bacterial species are linked to physiologic health along different axes. We review the role of diet quality, carbohydrate intake, fermentable FODMAPs, and prebiotic fiber in maintaining healthy gut flora. The implications are discussed for various conditions including obesity, diabetes, irritable bowel syndrome, inflammatory bowel disease, depression, and cardiovascular disease.

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This study was undertaken to determine whether the gravimetric method provided an accurate measure of water flux correction and to compare the gravimetric method with methods that employ nonabsorbed markers (eg, phenol red and were co-perfused in situ through the jejunum of 9 anesthetized rats (single-pass intestinal perfusion [SPIP]). Water absorption was determined from the phenol red, 14 C-PEG-3350, and gravimetric methods. The absorption rate constant (k a ) for Compound I was calculated. Both phenol red and 14 C-PEG-3350 were appreciably absorbed, underestimating the extent of water flux in the SPIP model. The average ± SD water flux (μg/h/cm) for the 3 methods were 68.9 ± 28.2 (gravimetric), 26.8 ± 49.2 (phenol red), and 34.9 ± 21.9 ( 14 C-PEG-3350). The (average ± SD) ka for Compound I (uncorrected for water flux) was 0.024 ± 0.005 min -1 . For the corrected, gravimetric method, the average ± SD was 0.031 ± 0.001 min -1 . The gravimetric method for correcting water flux was as accurate as the 2 "nonabsorbed" marker methods.

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