When weight is lost, the system works in the opposite direction: Less fat means reduced levels of circulating leptin, increased appetite, and reduced energy expenditure. (scientificamerican.com)
These authors speculated that, as for other endocrine systems (33,34), the CNS might interpret an increase in leptin pulse amplitude as a signal calling for a decrease in appetite independently from any change in the integrated circulating leptin concentration (32). (academic.oup.com)
It already has high circulating leptin, since its considerable fat stores are secreting it, but there is no receptor to accept it. (marksdailyapple.com)