Hormonal

Basal muscle sympathetic nerve activity (MSNA) correlates positively with plasma leptin concentration in healthy men, suggesting leptin acts as a peripheral signal to increase sympathetic outflow.

This research suggests that higher body fat leads to higher leptin, which in turn stimulates your sympathetic nervous system (your 'fight or flight' energy expenditure system). While this is a natural regulatory mechanism, the correlation is moderate, meaning other factors also drive your metabolic rate. It highlights that obesity involves complex hormonal signaling, not just 'calories in vs. calories out' in isolation.