The influence of early nutrition and growth on body composition in childhood and early adult life
There is increasing evidence that events early in life may 'programme' later body composition (BC) and health outcomes. The aim of the work presented in this thesis was to test the following hypotheses: (l) birthweight and growth in infancy programme specific components of BC in later life and therefore have differential effects on health outcomes (2) infant BC is differentially related to later BC, and is potentially involved in the programming process. These hypotheses were investigated in 2 cohorts (1) prospective follow-up during adolescence of subjects who had BC measurements during infancy (by stable isotope) as part of nutrition intervention studies (2) healthy children who participated in a BC reference study, with retrospective collection of early growth records. The main outcome was BC assessed by the four-component model. Secondary outcomes were cardiovascular risk factors (blood pressure, lipid profiles, and insulin resistance markers). 308 subjects aged 4.22-20.36 years were studied. Birthweight (regarded as a proxy for prenatal growth) was positively related to later height in both sexes, and positively associated with fat free mass (FFM) in boys. In contrast, postnatal growth during the first 6 months of life positively influenced later fat mass (FM) and central fat distribution, with a weaker effect on FFM. Whilst FM showed a consistent association with most cardiovascular risk factors except HDL-C, FFM showed a strong negative association with HDL-C, independent of FM and central fat distribution. In a smaller group (n=41), BC at 12 weeks of age showed no significant association with adolescent BC but SF during very early postnatal life (3 and 6 weeks) was related to later FFM and central fat distribution. Infant nutrition affected infant body composition, but I was unable to detect effects on later BC. Conclusion: I found differential effects of growth during different periods on later BC, measured using the 'gold standard' four-component model. The mechanism by which early growth 'programs' later BC possibly involves both prenatal and postnatal nutrition and warrants further investigation, since it could be useful in terms of designing effective early intervention to reduce obesity prevalence in childhood and adolescence. BC during adolescence has a differential impact on cardiovascular risk factors. Therefore, separate measurements of FM, FFM, and central fat distribution may offer more insight into the impact of body composition programming on health outcomes.