Among osteotrophic nutrients, proteins play an important role in bone development, thereby influencing peak bone mass. Consequently, protein malnutrition during development can increase the risk of osteoporosis and of fragility fracture later in life. Both animal and human studies indicate that low protein intake can be detrimental for both the acquisition of bone mass during growth and its conservation during adulthood. Low protein intake impairs both the production and action of IGF-I (Insulin-like growthfactor-I). IGF-I is an essential factorf or bone longitudinal growth, as it stimulates proliferation and difef rentiation of chondrocytes in the epiphyseal plate, and also for bone formation. It can be considered as a key factor in the adjustments of calcium-phosphate metabolism required for normal skeletal development and bone mineralization during growth. In healthy children and adolescents, a positive association between the amount of ingested proteins and bone mass gain was observed in both sexes at the level of the lumbar spine, the proximal femur and the midfemoral shaft. This association appears to be particularly significant in prepubertal children. This suggests that, like for the bone response to either the intake of calcium or weight-bearing exercise, the skeleton would be particularly responsive to the protein intake during the years preceding the onset of pubertal maturation.