Free · 22 pages · 38 cited sources
The Fasting Index Field Guide
What happens hour by hour, what breaks a fast, and where the evidence actually stops.
What is in it
Who should not fast
First, plain, and unhedged. The only part that is not optional.
Hour by hour
0–4 h, 4–16 h, 16–24 h, 24–48 h, 48–72 h and beyond, with a plate of the whole sequence.
The four methods
16:8, 5:2, OMAD and alternate-day drawn on one honest axis — including who each one fails.
Twenty verdicts
Does it break a fast? Answered four times, because the answer depends on why you are fasting.
Breaking a fast
What actually matters, and the point at which it stops being a matter of preference.
Where the evidence stops
Strong, moderate, weak, and absent. Including the three claims to be most careful about.
Why this one is different
Almost every page on the open web answering “does X break a fast” is published by a company that sells X. On the query we measured, six of the eight sources Google’s AI Overview cited were supplement retailers writing about their own product.
This guide sells nothing you can swallow, and it never will. The only two substances it recommends are salt and water, and nobody pays us for those.
It also tells you where its evidence stops. There is a chapter on what is strong, what is weak, and what is not established in humans at all — including the sixteen-hour autophagy figure, which is not a human finding and traces back to a study in mice.
Fasting is not safe for everyone
There is a longer one
The Complete Fasting Reference is 76 pages and 59 cited sources: the physiology past 72 hours, refeeding in full, the Ramadan chapters, and every trial behind the claims with its limitations stated.
See what is in it