Library.

“The "calories in, calories out" (CICO) model is an oversimplification of the metabolic processes that govern fat loss and fat accumulation in the human body.”

The scientific literature broadly supports the view that the simple "calories in, calories out" framing omits significant biological complexity—including adaptive thermogenesis, hormonal regulation of appetite and metabolism, and variable metabolic efficiency of different macronutrients. However, energy balance remains a valid physical constraint on weight change; the claim is accurate in calling CICO an oversimplification of metabolic processes, but should not be read as suggesting energy balance is biologically false.

“Intermittent fasting slows down human metabolism.”

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.