Ghrelin and peptide YY (PYY) are newly recognized gut peptides involved in 
appetite regulation. Plasma ghrelin concentrations are elevated in fasting and 
suppressed following a meal, while PYY concentrations are suppressed in fasting 
and elevated postprandially. We determine whether ghrelin and PYY are altered by 
a low-fat, high-carbohydrate (10% fat, 75% carbohydrate) or moderate-fat, 
moderate-carbohydrate (35% fat, 50% carbohydrate) diet and; whether these 
peptides are affected by intense endurance running (which is likely to 
temporarily suppress appetite). Twenty-one endurance-trained runners followed a 
controlled diet (25% fat) and training regimen for 3 days before consuming the 
low-fat or isoenergetic moderate-fat diet for another 3 days in random 
cross-over fashion. On day 7 runners underwent glycogen restoration and then 
completed a 90-minute pre-loaded 10-km time trial on day 8, following a control 
breakfast. Blood samples were obtained on days 4 and 7 (fasting), and day 8 
(non-fasting) before and after exercise for analysis of ghrelin, PYY, insulin 
and growth hormone (GH). Insulin, GH, Ghrelin and PYY changed significantly over 
time (p < 0.0001) but were not influenced by diet. Ghrelin was elevated during 
fasting (days 4 and 7), while insulin and PYY were suppressed. Following the 
pre-exercise meal, ghrelin was suppressed ~17% and insulin and PYY were elevated 
~157 and ~40%, respectively, relative to fasting (day 7). Following exercise, 
PYY, ghrelin, and GH were significantly (p < 0.0001) increased by ~11, ~16 and 
~813%, respectively. The noted disruption in the typical inverse relationship 
between ghrelin and PYY following exercise suggests that interaction of these 
peptides may be at least partially responsible for post-exercise appetite 
suppression. These peptides do not appear to be influenced by dietary fat 
intake.