About FastingPhases
A free, independent reference for the metabolic phases of fasting. No accounts. No products. No affiliate deals. Sources cited on every claim.
What this site is
FastingPhases.com is a free educational reference that shows what is actually happening in your body at each hour of an extended fast — from the post-meal "fed state" through ketosis, growth hormone elevation, and autophagy. The calculator on the homepage maps any hour you enter to its corresponding metabolic phase, with citations to the peer-reviewed research behind each phase boundary.
This site is intended for adults curious about fasting, people already practicing intermittent or extended fasting, and clinicians who want a clear, citation-backed reference to share with patients.
What we don't do
- No accounts. No email signup. No login. Nothing personal stored — every calculation runs entirely in your browser.
- No products. We don't sell electrolyte powders, fasting apps, supplements, books, courses, or coaching.
- No affiliate deals. No Amazon Associates links, no kickbacks for product mentions. The site is monetized solely through Google AdSense advertising.
- No medical advice. The site explains physiology and surfaces published research. It does not substitute for clinical guidance, especially for people with eating disorders, pregnancy, breastfeeding, diabetes, or other metabolic conditions.
Editorial principles
Cite primary research
Every phase boundary timing on the homepage chart traces to a peer-reviewed study listed in the Sources section. Where the science is uncertain — notably autophagy timing in humans — we mark those phases with hatched bars and "emerging evidence" labels rather than false precision.
Distinguish primary from popularizers
Authors like Jason Fung, Thomas DeLauer, and Dominic D'Agostino have done valuable work introducing fasting science to the public. We name them as framework references but treat the underlying peer-reviewed studies as authoritative on factual claims.
Surface the safety signals
Fasting carries real risks for some people. Every results page includes a green/yellow/red signal reference for when to keep going, when to pause, and when to break the fast immediately. Severe symptoms (chest pain, fainting, persistent palpitations) get an explicit emergency-services prompt.
Acknowledge what we don't know
Many widely-shared claims about fasting (precise autophagy onset, immune system "reset" hours, optimal protein refeed) have weaker evidence than the popular literature suggests. We say so, in the relevant places, rather than presenting contested claims as settled science.
How we operate
FastingPhases is run by a small editorial team. We publish under the organization name rather than individual bylines because the value of the site comes from the citations and the methodology, not from any single author's credentials. The site is a static HTML application hosted on AWS — there is no database of users, no CRM, no email list, no account system.
The site is monetized exclusively through Google AdSense — display ads at the top, middle, and bottom of pages. We do not control which specific ads are shown. The presence of an ad here is not an endorsement of the advertiser, and we have no business relationships with any company whose ads may appear.
How the site stays current
The Sources section on the homepage is reviewed annually for new published research that would refine the phase boundaries shown in the chart. When peer-reviewed evidence shifts a phase timing meaningfully (for example, the recent Endocrine Reviews 2025 review of fasting and metabolic health), the chart and underlying calculations are updated, and the previous version's data is preserved in the Methodology page.
For the full data lineage and assumptions, see the Methodology page.