Fig. 1

Alternative stable states and critical transition in the gut microbiota–host symbiosis. a Alternative stable states representing health (symbiosis) (left) or (pre-)disease (altered symbiosis) (right). The cycle in the middle represents a vicious circle of self-enhancing deterioration of symbiosis, leading to critical transition to an alternative stable state of altered symbiosis. Changing alimentary habits could start this self-enhancing process through reduction of microbiota diversity or by increasing permeability of the mucosal barrier. Antibiotics can do the same through reduction of microbiota diversity. b Schematic representation of alternative stable states as beads in a landscape. T indicates a tipping point. In case of (pre-)disease (altered symbiosis), symbiosis may be restored through dual action via (a), (b), and (c) (see text for explanation). c Alternative stable states (top and bottom part of the curve) are different states that can exist under identical external conditions. The dashed line represents a tipping point (cf panel b: T). When the conditions change to a point beyond x, the system will switch to the alternative stable state (altered symbiosis). If the starting point (symbiosis) is situated in the bi-stable range of conditions, setting back the conditions to those that reigned before the switch to the state of altered symbiosis is not sufficient to shift the system back to its original state of symbiosis