We examined the influence of multi‐nutrient fortification of mother's milk (MM + MNF) compared to supplementation with calcium and phosphorus (MM + CaGP) alone in hospital (in a randomized trial), and of breastfeeding (post‐MM) compared to formula feeding (post‐FF) after hospital discharge with a descriptive analysis of growth and body composition to 1 y corrected age in preterm infants. Anthropometry, nutrient intakes and whole body bone mineral content, lean and fat mass were determined at four time points in the first year after term corrected age. Body composition was determined with dual energy X‐ray absorptiometry. MM + MNF compared to MM + CaGP for preterm infants in the early neonatal period did not appear to influence growth or body composition in the first year. Growth in post‐MM and post‐FF groups was within the normal range of growth references derived from term infants fed mother's milk. Post‐MM infants had lower whole body bone mineral content (132.3 ± 10.4 g) at 6 months corrected age when compared to post‐FF infants (159.4 ± 14.1 g) and greater percent fat mass to 12 months corrected age. These differences may result from the lower calcium, phosphorus and protein intakes in post‐MM compared to post‐FF infants. Our findings demonstrate that dietary practices after hospital discharge likely have a greater impact on body composition in prematurely born infants than dietary practices in hospital. Whether the observed differences in body composition between breastfed and formula‐fed preterm infants have any long‐term consequences requires further investigation.