Evidence check: CLOCK in the context of weight loss

CLOCK gene variants (e.g., rs1801260) are linked to circadian rhythm and have been associated in GWAS with modestly higher BMI and obesity risk (OR ~1.1–1.2). Effect sizes are small and not diagnostic. Mechanistically, CLOCK regulates metabolic gene expression, but direct evidence that genotyping improves weight loss is lacking. Randomized trials show that sleep duration and meal timing (e.g., early eating) can influence weight loss, independent of CLOCK genotype. Direct-to-consumer DNA tests marketing CLOCK as a 'fat-burning gene' overstate clinical utility. Evidence is mechanistic/GWAS, not human-strong. Caveat: No supplement or diet is warranted based solely on CLOCK genotype. Consistent sleep schedules and calorie balance remain the most evidence-based approach.