Hormones like ghrelin (hunger) and leptin, GLP-1 and PYY (fullness) carry messages between gut, fat tissue and brain.
What affects fullness
Protein, fiber and water-rich foods tend to be more filling per calorie. Short sleep can increase hunger signals.
A note
This app never scores eating less. Regular, adequate meals support energy, mood and health.
Evidence & sources
Short sleep duration has been associated with lower leptin and higher ghrelin levels. Evidence: limited. Known: Population study of ~1,000 adults. Unknown: Observational; causality unclear. Source: Taheri et al., PLoS Medicine, Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased BMI (2004).