Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans

Researchers compared adults who had followed calorie-restricted diets for years, adults eating low-protein diets, and adults eating typical diets. They measured IGF-1, a growth-related hormone, and IGFBP-3, a blood protein that carries IGF-1. Eating fewer calories did not clearly lower these measures when people still ate enough protein. Eating less protein was linked to lower IGF-1 and IGFBP-3 levels. The groups were not randomly assigned, so other lifestyle differences could have affected the results.

What this means for you: This does not show that eating less protein helps people live longer, and too little protein can harm muscle health. It offers no strong reason to buy a low-protein product or sharply cut calories to change these blood markers.