Time-restricted feeding — Circadian-Aligned Fasting

Time-restricted feeding (TRF) enforces a daily fasting period that aligns feeding with circadian rhythms, triggering a metabolic switch from glucose utilisation to fatty acid oxidation and ketogenesis. During the fasting window, the depletion of hepatic glycogen reduces insulin and IGF-1 signalling, which subsequently downregulates the mTOR pathway and upregulates AMPK. This energy deficit activates sirtuins (such as SIRT1 and SIRT3) and transcription factors like FOXO and PGC-1α, promoting autophagy, mitochondrial biogenesis, and cellular repair. By consolidating nutrient intake, TRF also reinforces peripheral circadian clocks, improving glucose tolerance and reducing systemic inflammation independent of total caloric restriction.

Multiple human trials demonstrate that time-restricted eating (typically a 10-hour window) improves metabolic parameters, including reductions in body weight, blood pressure, and atherogenic lipids, particularly in individuals with metabolic syndrome. A 2020 trial in Cell Metabolism showed significant cardiometabolic benefits in patients with metabolic syndrome. However, evidence for direct lifespan extension in humans remains unestablished, with current data primarily supporting healthspan improvements through metabolic regulation.

Typical protocols restrict all caloric intake to an 8–10 hour window daily (e.g., 10:00 AM to 6:00 PM), with fasting for the remaining 14–16 hours. Hydration with water, black coffee, or plain tea is maintained during the fasting period. Consistency in the timing of the eating window, particularly aligning it with daylight hours (early time-restricted eating), may optimise circadian alignment.

Generally well-tolerated, but may cause transient fatigue, irritability, or headaches during the initial adaptation phase. Contraindicated for pregnant or breastfeeding women, individuals with a history of eating disorders, and those underweight. Patients on medications that lower blood glucose (e.g., insulin, sulfonylureas) must consult a physician due to the risk of hypoglycaemia during the fasting window.

Key Papers