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.)