Leptin is part of our complex hunger signaling feedback system. Leptin levels are typically high in obese people, but because the signaling is impaired, they may still experience hunger even though body fat levels are high.
Children that were required to fast for diagnostic lab testing experienced a steady fall in leptin levels from the beginning of fasting. Leptin levels where also correlated with insulin levels.
The common thinking today is that leptin does not begin to fall significantly until we”ve been dieting for a while, but this study contradicts that. Also, insulin is an appetite stimulant, but because of it”s impact on leptin it also helps to signal a fed state to the brain.