Body stages Also worth knowing Card 5 of 5
Explainer card
Longevity and body size
Fasting extends lifespan in laboratory animals. There is no evidence that it does so in humans. Across 99 trials, intermittent fasting forms are roughly equal to continuous daily restriction for body size, and observational data in older adults show higher mortality with very short eating windows.
Background reading, never a stage. The timer never shows it, and it is not tied to any hour of a fast. In the app it sits under the stages, in Also worth knowing.
Sources
- Cochrane 2021Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database Syst Rev, 2021.
- BMJ 2025 network meta-analysisIntermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ, 2025.
- Mao 2025Association of Eating Window With Mortality Among US Adults: Insights From a Nationally Representative Study. Aging Cell, 2025.
What studies measured, not a reading of your own body. Stop and seek help if you feel unwell; the signs to stop for are listed under Stop signs on the safety page.
Evidence edition 1.0 · last updated · How this is written