Fig. 1

Possible role of the gut microbiota in the pathogenesis of anorexia nervosa (AN). Premorbid traits, such as compulsive personality, perfectionism, and drive for thinness, and psychosocial stressors play a crucial role in AN development [74]. Consequently, changes in dietary habits and altered intake of food ingredients, induced by dieting, lead to a dearth of essential amino acids [60] and “gut dysbiosis” [45,46,47,48, 51,52,53,54,55,56]. Physical and psychological stresses accompanying extreme weight loss may also affect the disturbed microbial ecology of the gut [89, 90]. Moreover, gut dysbiosis, together with the stresses, also induces constipation by impairing gut motility function [49, 50]. Prolonged constipation with gut dysbiosis elevates uremic toxins [60], such as p-cresol, which is possibly involved in poor weight gain [65] and psychiatric symptoms [69]. Decreased short chain fatty acids (SCFA), especially acetate, derived from gut dysbiosis [48] may also contribute to impaired weight control [79] and persistent anxiety [81, 82]. Finally, hyperactivity, a key characteristic of AN [75,76,77], is potentially induced by an insufficient intake of essential amino acids, such as tryptophan, and further perpetuates low body weight via increasing calorie expenditure