BACKGROUND & AIMS: Growth hormone (GH) affects body composition by a relatively reduced fat mass and increased fat free mass. The intake of protein as well as the specific amino acids arginine and lysine potently stimulate GH secretion. This study investigated associations between intakes of protein, arginine, lysine and subsequent 6-year change in body composition among 8-10-year-old children. METHODS: Data of 364 children were collected from Odense, Denmark, during 1997-1998 and 6-year later as part of the European Youth Heart Study. Body mass index among children was subdivided by fat free mass index (FFMI) and fat mass index (FMI), based on skinfold measurements. Dietary intake was estimated via 24h recall. Associations between intakes of protein as well as arginine, lysine and change in FFMI and FMI were analysed by multiple linear regressions, adjusted for social economic status, puberty stage and physical activity level. RESULTS: Among lean girls inverse associations were found between protein as well as arginine and lysine intake and change in fat mass index (beta=-1.12+/-0.56, p=0.03, beta=-1.10+/-0.53, p=0.04, beta=-1.13+/-0.51, p=0.03 respectively). Furthermore among girls with a body mass index in the 5th quintile, protein intake was associated with DeltaFFMI (p=0.04), and more specific when LYS intake was high, ARG intake was associated with DeltaFFMI (p=0.04). CONCLUSION: Among girls high protein intakes may decrease body fat gain and increase fat free mass gain, depending on the available amounts and combinations of arginine and lysine.