The Short Version
The claim that intermittent fasting slows human metabolism is not supported by the scientific evidence. Multiple peer-reviewed studies from NIH, Harvard, and the Salk Institute show that standard IF protocols maintain or even increase resting metabolic rate and activate beneficial metabolic pathways like fat oxidation and AMPK signaling. The only scenarios where metabolism may temporarily dip involve prolonged or poorly structured fasting — not typical IF — and any reduction reverses upon refeeding. The claim presents an edge-case risk as a general rule.