Figure 6.5: Blood levels of the hormone PYY in obese and lean human subjects Blood levels of PYY were found to be lower in obese subjects than in lean subjects. After eating a meal, lean subjects showed a much larger increase in PYY than did obese subjects. Researchers believe that this difference may be a cause of obesity, as PYY acts on the brain to suppress appetite.

(Based on data from Batterham et al., 2003.)