- In a cohort of 36 young females with anorexia, levels of ghrelin and peptide YY were higher than in 32 controls in the fasting state, and levels of brain-derived neurotrophic factor (BDNF) were lower, confirming previous research
- After a standardized meal, the ghrelin and peptide YY area under the curve was significantly higher and the BDNF area under the curve was significantly lower in the anorexia group than in controls
- Within the anorexia group, but not the control group, the greater the reduction in ghrelin or peptide YY after the meal, the greater the reduction in scores of prospective food consumption
- During a modified Cookie Taste Test, there was a trend in the anorexia group for a positive association between levels of BDNF and kilocalories consumed
Levels of several appetite-regulating hormones are known to be different in patients with anorexia nervosa than in normal-weight controls. These include increased ghrelin (stimulates appetite) because of adaptive response by the body to increase caloric intake, increased peptide YY (PYY), which is anorexigenic (it induces satiety), and decreased brain-derived neurotrophic factor (BDNF), which is primarily anorexigenic but may affect both homeostatic and hedonic appetite.
Madhusmita Misra, MD, MPH, division chief of Pediatric Endocrinology at Massachusetts General Hospital, and colleagues recently became the first to examine how changes in these hormones after a meal relate to hunger and satiety in adolescents with anorexia. In Psychoneuroendocrinology, they report that changes in ghrelin and PYY were associated with reductions in prospective food consumption (how much one thinks she can eat), while reductions in BDNF were associated with reduced pleasure in food intake.
The researchers studied 36 females with anorexia and 32 normal-weight female controls who were 10 to 22 years old. After fasting overnight, participants were given a choice of three breakfasts (about 400 kcal), which they were asked to eat within 15 minutes. After completion, staff weighed any leftovers to determine caloric intake. Blood was drawn immediately before the meal and 30, 60 and 120 minutes after the start of eating to measure the area under the curve of each hormone.
Changes in Hormone Levels
- Ghrelin was significantly higher in the anorexia group than in the control group at all timepoints. Percent change from baseline did not differ significantly between groups at any timepoint
- PYY was significantly higher in the anorexia group at baseline and 30 minutes, and trended higher at 60 and 120 minutes. Percent change from baseline trended lower in the anorexia group at 120 minutes
- BDNF was significantly lower in the anorexia group at baseline and 60 minutes. Percent change from baseline was significantly higher in the anorexia group at 120 minutes
Visual Analog Scales
Five minutes before the meal and 20 to 25 minutes after completion, participants completed visual analog scales that measured prospective food consumption ("How much do you think you can eat?"), hunger, satiety and hedonic appetite ("How strong is your desire to eat your favorite food?"). They found:
- Before breakfast, the anorexia group reported reduced hedonic appetite, compared with controls, and lower scores on the question about prospective food consumption. After breakfast, there were no differences between groups in those scores or in the pre- to post-breakfast change in appetite
- Within the anorexia group, the greater the reduction in ghrelin or PYY after breakfast, the greater the reduction in scores of prospective food consumption. Those associations were not observed in controls
- There were no associations between changes in ghrelin, PYY or BDNF levels and changes in hunger, satiety and hedonic appetite before and after breakfast
Cookie Taste Test
Three hours after the start of breakfast and 30 minutes after initiation of a standard snack, participants were asked to taste as much of three different cookies as needed to rate the cookies on various dimensions such as sweetness and likability. Afterward, the amount of cookies each participant consumed was weighed to serve as a measure of hedonic appetite.
The anorexia group consumed fewer kilocalories than the control group, and there was a trend for a positive association in the anorexia group between BDNF levels and kilocalories consumed (r = 0.398, P = .054). There were no significant relationships between ghrelin or PYY levels and kilocalories consumed in either group.
There appears to be a complex interplay of biological mechanisms that underlie disordered eating and perceptions of appetite. Larger studies of appetite-regulating hormones are needed to support drug development for anorexia, such as by using functional MRI to determine which brain areas are activated in homeostatic versus hedonic appetite.