Basal Metabolic Rate
The minimum number of calories the body requires at rest to maintain basic life functions. BMR is influenced by body composition (more muscle = higher BMR), age, sex, and thyroid function. Significant weight loss reduces BMR, which contributes to weight regain when treatment is discontinued.
Technical Context
BMR accounts for approximately 60-70% of total daily energy expenditure and is primarily determined by lean body mass (muscle, organ tissue). Weight loss reduces BMR through: loss of metabolically active lean mass (each kg of lean mass accounts for approximately 13-28 kcal/day), and metabolic adaptation (reduction in BMR beyond what is predicted from the change in body composition — the body becomes more energy-efficient, potentially through reduced sympathetic nervous system activity, lower thyroid hormone levels, and decreased leptin). This metabolic adaptation persists for years after weight loss and creates a thermodynamic environment favouring weight regain. GLP-1 RA discontinuation weight regain is partly driven by this persistent metabolic adaptation combined with restored appetite signalling. Understanding metabolic adaptation is important for patient counselling about realistic long-term outcomes and the rationale for ongoing treatment.