Figure 4.

Nutrient intake and stool consistency are sufficient to explain microbiota variation in healthy humans. The relative abundance of Bacteroidetes (color code) in a simplified microbiota consisting of 2 phyla changes drastically even for small changes in nutrient uptake and epithelial water absorption (which is related to stool consistency in a linear way). The solid white lines denote standard estimates for healthy humans as used in our model, the area inside the dashed line is the variation in nutrient intake and stool consistency considered healthy. Colors from red (almost only Bacteroidetes) to blue (almost no Bacteroidetes) are included in that area, indicating that small physiological changes that will not affect the perceived health status of the host can have strong effects on microbiota composition. The strong dependence of stool consistency on B/F ratios recapitulates recent observations.^38,39 Figure adapted from.¹⁷