Relationship between birth weight and body composition, energy metabolism,and sympathetic nervous system activity later in life

Objective: Epidemiological studies suggest that high birth weight might be associated with an increased risk of obesity later in life. Programming of metabolic, endocrine, and/or autonomic pathways during intrauterine develop ment has been proposed to explain this association. Research Methods and Procedures: To determine the relationship between birt h weight and body composition and energy metabolism later in life, we measu red fat mass and fat-free mass (hydrodensitometry or double-energy X-ray ab sorptiometry), 24-hour energy expenditure, sleeping metabolic rate, and 24- hour respiratory quotient (respiratory chamber) in 272 adult nondiabetic Pi ma Indians (161 males/ III females, age 25 +/- 5 years, mean +/- SD). In th ese subjects, birth weight varied over a wide range (2000 to 5000 g). Indiv iduals known to be offspring of diabetic pregnancies were excluded. In 44 o f the 272 subjects, muscle sympathetic nerve activity was assessed by micro neurography. Results: Birth weight was positively correlated with adult height (r = 0.20 , p < 0.001) and fat-free mass (r = 0.21, p < 0.001), but not with fat mass (r = 0.01, not significant). Sleeping metabolic rate, adjusted for age, se x, fat-free mass, and fat mass, was negatively related to birth weight (r - 0.13, p < 0.05), whereas adjusted 24-hour energy expenditure (r = 0.07, not significant) and 24-hour respiratory quotient (r = -0.09, not significant) were not. There was no relationship between birth weight and muscle sympat hetic nerve activity (r = 0.12, not significant, n = 44). Discussion: In Pima Indians who are not offspring of diabetic pregnancies, high birth weight is associated with increased height and lean body mass, b ut not with increased adiposity later in life. Although high birth weight m ay be associated with relatively low resting energy expenditure, it is not associated with major abnormalities in 24-hour energy metabolism or with lo w muscle sympathetic nerve activity later in life.