How growth hormone, fasting, and muscle preservation work together.
What the evidence says
- Integrated 24-h GH concentration rises during a 5-day fast — *the paper's own figures, with their dispersion: "2.82±0.50 vs. 8.75±0.82 µg·min/ml; P = 0.0002" in six men. "3.1-fold" is this library's arithmetic, not the paper's word — Ho et al. do not express the five-day comparison as a fold change; use their two values, or say "roughly threefold" and mark it as derived. Their one GH fold figure is a day-1 statement — see below. And the rise has already happened by the first fasted day, which the paper quantifies: "increased after 1 d of fasting (2.82±0.50 vs. 7.82±1.12, control vs. day 1; P = 0.0009) and remained elevated on day 5" — so day 1 already carries most of the five-day rise. What continues to climb to day 5 is the nonpulsatile* component of GH release, fourfold on day 1 to tenfold on day 5[1]
- 2-day fast: 24-hour GH production rate increases 5-fold (78 → 371 μg/Lv) *in normal men*[2]
- *On Nørrelund's review*, GH's protein-sparing effect works indirectly: GH → lipolysis → FFA mobilisation → protein conservation[3]
- *The review's framing: fat becomes the primary fuel and GH acts as a master fuel switch toward lipid utilisation, decreasing glucose and protein oxidation — the oxidation clause traces to no held file: `cgh03`'s notes report the switch only as "from carbohydrate to lipid utilization"* (marked 2026-09-10, following `cgh03`)[3]
- *The review proposes that fasting and stress may represent GH's natural metabolic domain rather than its role in growth — traced to no held file*: `cgh03`'s notes do not carry it (marked 2026-09-10)[3]
- *The lipolysis half is now confirmed first-hand, and the protein-sparing half is not. Blocking the GH receptor during a 36-hour fast suppressed lipid mobilisation and oxidation — free fatty acids 1226 ± 83 vs. 1074 ± 65 µmol/liter (P = 0.03) and ketone bodies 3080 ± 271 vs. 2015 ± 235 µmol/liter (P ≤ 0.01) — while protein metabolism was unaffected*, assessed by isotope tracer rather than crudely[4]
- *That is a limit on the claim, not a refutation of it. `cgh05` tested 36 hours under partial receptor blockade in 10 healthy young men; a protein-sparing effect over longer fasts or fuller blockade is not what it measured. The authors' own conclusion is narrow: GH receptor blockade "selectively suppresses lipid mobilization and oxidation after short-term fasting"*[4]
- *`cgh05` is unusually direct evidence on `cgh03`'s claim*: Helene Nørrelund is `cgh03`'s sole author and `cgh05`'s second author — the same investigator, the same question, first-hand rather than in synthesis[4]