IGF 1: Miracle Hormone or Health Hazard? Diet vs Disease IGF 1 LR3 does not promote growth in late gestation growth restricted fetal sheep American Journal of Physiology Endocrinology and Metabolism American Physiological Society All Natural Hormone Hacks for Muscle Growth & Fat Loss: T, HGH, Cortisol, IGF 1, Insulin, T3 & More! What is IGF 1 LR3?, Insulin Like Growth Factor 1 Long R3 (IGF 1 LR3) is a modified version of IGF 1 with a longer half life, making it significantly more potent and effective for muscle growth, If your priority is building muscle, IGF 1 is what really matters.