What this library can and cannot show about muscle during a fast — and why the protein-sparing half of the usual account is not established here.
What the evidence says
- RELAYED THROUGH A BOOK, not reported by one: a 70-day alternate-daily-fasting trial in which fat mass decreased 11.4% with lean mass unchanged — the figure reaches this library through Fung’s account of that trial, not through the trial[1]
- Fung’s own words on page 243 — ”Growth hormone increased to maintain” muscle mass — and the library now holds a primary that tests this directly and does not support it: in `cgh05`, blocking the GH receptor through a 36-hour fast suppressed lipid mobilisation while protein metabolism was unaffected. See `kgh02` for the standing[1],[2]
- Also relayed: one-meal-per-day studies reporting significantly more fat loss than three meals at the same calories, with no muscle loss[1]
- Also Fung’s assertion, in his voice: fat is burned first and muscle breakdown occurs only when body fat becomes extremely low — the page argues it rhetorically (”assume the human body is so stupid?”) rather than reporting a study[1]
- The same assertion restated — ”The body preserves muscle mass” until fat stores are very low; this and the bullet above are one claim from one page, not two findings[1]
- *Alternate-day fasting costs no more lean mass than daily calorie restriction — and neither preserved it. In the 24-week trial, FFM fell in both intervention arms (ADF −1.2 ± 0.4 kg; CR −1.8 ± 0.8 kg) and rose in the control group (+0.3 ± 0.4 kg); the changes were not significantly different between groups. What increased in both arms was the FFM-to-total-mass ratio* (0.03 in each, P<0.01) — the proportion of the body that is lean, which rises when fat falls faster[3]
- Review of IF protocols: 3-7% weight loss with lean mass preserved across ADF, WDF, and TRF[4]
- IF produces marked reductions in visceral fat with retention of lean muscle mass, with improved insulin sensitivity independent of overall calorie reduction[5]