Background: Over the past decades, the preterm birth rate has increased, mostly due to a rise in late and moderate preterm (LMPT, 32–36 weeks gestation) births. LMPT birth affects 6–7% of all births in the United Kingdom and is associated with increased morbidity risk after birth in infancy as well as in adulthood. Early life nutrition has a critical role in determining infant growth and development, but there are limited data specifically addressing LMPT infants, which was the rationale for the design of the current study.Objective: The Feeding Late and Moderate Infants and Growth Outcomes (FLAMINGO) study aims to improve understanding of the longitudinal growth, nutritional needs, and body composition of LMPT infants as well as their microbiome development and neurodevelopment. In addition, having a nested non-inferiority trial enables evaluation of the nutritional adequacy of a concept IMF with large milk phospholipid-coated lipid droplets comprising dairy and vegetable lipids. The primary outcome of this RCT is daily weight gain until 3 months corrected age.Methods: A total of 250 healthy LMPT infants (32+0–36+6 weeks gestational age) with birth weight 1.25–3.0 kg will be recruited to the cohort, of which 140 infants are anticipated to be enrolled in the RCT. During six visits over the first 2 years of life, anthropometry, body composition (using dual energy X-Ray absorptiometry), feeding behavior, and developmental outcomes will be measured. Saliva and stool samples will be collected for oral and gut microbiota assessment.Discussion: The FLAMINGO study will improve understanding of the longitudinal growth, body composition development, and feeding characteristics of LMPT infants and gain insights into their microbiome and neurodevelopment.Study Registration:www.isrctn.com; Identifier ISRCTN15469594.