Hypothesis

Intermittent fasting (IF) modulates hepatic IGF-1 production such that GH pulses during somatopause retain anabolic effects on lean mass while avoiding the insulin‑resistant state seen with continuous GH elevation.

Mechanistic rationale

• Somatopause is driven by reduced GHRH and increased somatostatin tone, yielding low‑amplitude GH pulses 5.
• GH stimulates hepatic IGF-1 synthesis; elevated IGF-1 activates PI3K/Akt/mTOR, promoting serine phosphorylation of IRS-1 and impairing insulin signaling 3.
• IF lowers circulating IGF-1 through reduced nutrient‑sensing (↓ insulin, ↑ FGF21) and increased IGFBP-1, which sequesters IGF-1 and diminishes its receptor activation 1.
• Lower IGF-1 reduces mTORC1 activity in muscle, decreasing IRS-1 serine phosphorylation and preserving insulin‑stimulated AKT activation, thus counteracting GH‑induced insulin resistance.
• The resulting state preserves GH‑mediated lipolysis and protein synthesis without the metabolic maladaptation observed in GH replacement trials.

Testable predictions

1. In older adults, a 16:8 IF regimen combined with a GH secretagogue (e.g., oral ghrelin agonist) will increase lean‑mass gains comparable to GH secretagogue alone, but will produce significantly lower fasting insulin and HOMA‑IR 3.
2. Hepatic IGF-1 mRNA expression will be reduced after 4 weeks of IF, correlating with improvements in peripheral insulin sensitivity measured by hyperinsulinemic‑euglycemic clamp.
3. Subjects receiving GH secretagogue without IF will show elevated IGF-1 and increased serine‑307 phosphorylation of IRS-1 in skeletal muscle biopsies, whereas the IF group will not.

Falsifiability If IF fails to lower IGF-1 or does not ameliorate GH‑associated insulin resistance (i.e., HOMA‑IR remains unchanged or worsens relative to secretagogue alone), the hypothesis is refuted.

Broader implications This framework suggests that longevity‑promoting attenuated GH/IGF-1 signaling can be achieved pharmacologically not by blunt GH suppression but by timing nutrient intake to modulate hepatic IGF-1 bioavailability, thereby rescuing the anabolic promise of GH while preserving metabolic health.