PYY Levels and Relationship to Appetite Across Different Presentations of Anorexia Nervosa

Objectives: While the pathophysiology of eating disorders is not well understood, there is evidence that anorexigenic peptide YY (PYY) may play a role. We have shown that PYY levels are high in individuals with anorexia nervosa (AN) and associated with subjective appetite. However, it is unclear whether this represents a general characteristic across AN presentations. Here we investigate PYY levels and their associations with subjective appetite in individuals with atypical (atypAN), binge/purge type (AN-BP), and restricting type (AN-R) AN compared to healthy controls (HC). We hypothesized that PYY levels would be high in all AN presentations compared to HC and associated with subjective appetite. Methods: We performed a cross-sectional study of 106 females (26 atypAN, 11 AN-BP, 29 AN-R and 40 HC, age 10-22 yrs). Research diagnoses were conferred using the Eating Disorder Examination. Fasting blood was drawn for PYY and visual analog scales were administered to assess hunger and desire to eat one’s favorite food. We performed Wilcoxon test to determine between-group differences in clinical characteristics. Spearman’s correlation coefficient was used to determine the relationship between PYY levels and appetite within each group. Results: Mean age±SD of atypAN (18.3±3.3 yrs) and AN-BP (19.9±1.5 yrs) did not differ (ps≥0.11) while AN-R (19.5±2.4 yrs) were older (p=0.013) than HC (17.8±3.1 yrs). BMI was lower in atypAN (18.7±1.2 kg/m(2)), AN-BP (17.3±0.8 kg/m(2)), and AN-R (16.6±1.0 kg/m(2)) than in HC (21.3±2.0 kg/m(2); ps<0.0001). Fasting PYY levels were higher in atypAN (107.4±40.8 pg/mL), AN-BP (118.4±56.8 pg/mL) and AN-R (124.1±48.5 pg/mL) than HC (83.2±31.7 pg/mL, ps≤0.045). Hunger and desire to eat one’s favorite food were lower in atypAN and AN-BP compared to HC (ps≤0.042). Between group differences in PYY and appetite remained significant after controlling for age (ps≤0.032). The relationship between PYY and hunger was negative in AN-BP (ρ= -0.71, p=0.012), positive in AN-R (ρ=0.40, p=0.035), and not significant in atyp AN (ρ=0.02, p=0.90). The relationship between PYY and desire to eat favorite food was negative in AN-BP at trend level (ρ=-0.56, p=0.071), positive in AN-R (ρ=0.52, p=0.005), and not significant in atypAN (ρ=0.09, p=0.65). Conclusions: Compared to HC, fasting PYY levels were higher and appetite lower in all AN presentations. Higher fasting PYY levels were associated with lower appetite in AN-BP and greater appetite in AN-R, while no relationship was found in atypAN. The absence of an association in atypAN, which includes females who do not meet low weight criteria for AN-R or AN-BP, may reflect opposing relationships in those who restrict vs. binge/purge. Future research is required to further understand the differences in relationships between PYY levels and subjective appetite across AN presentations.