Associations of infant feeding with trajectories of body composition and growth

Abstract

Background: The extent to which breastfeeding is protective against later-life obesity is controversial. Little is known about differences in infant body composition between breastfed and formula-fed infants, which may reflect future obesity risk.Objective: We aimed to assess associations of infant feeding with trajectories of growth and body composition from birth to 7 mo in healthy infants.Design: We studied 276 participants from a previous study of maternal vitamin D supplementation during lactation. Mothers used monthly feeding diaries to report the extent of breastfeeding. We measured infants' anthropometrics and used dual-energy X-ray absorptiometry to assess body composition at 1, 4, and 7 mo. We compared changes in infant size (z scores for weight, length, and body mass index [BMI (in kg/m²)]) and body composition (fat and lean mass, body fat percentage) between predominantly breastfed and formula-fed infants, adjusting in linear regression for sex, gestational age, race/ethnicity, maternal BMI, study site, and socioeconomic status.Results: In this study, 214 infants (78%) were predominantly breastfed (median duration: 7 mo) and 62 were exclusively formula fed. Formula-fed infants had lower birth-weight z scores than breastfed infants (-0.22 ± 0.86 and 0.16 ± 0.88, respectively; P < 0.01) but gained more in weight and BMI through 7 mo of age (weight z score difference: 0.37; 95% CI: 0.04, 0.71; BMI z score difference: 0.35; 95% CI: 0, 0.69), with no difference in linear growth (z score difference: 0.05; 95% CI: -0.24, 0.34). Formula-fed infants gained more lean mass (difference: 303 g; 95% CI: 137, 469 g) than breastfed infants, but not fat mass (difference: -42 g; 95% CI: -299, 215 g).Conclusions: Formula-fed infants gained weight more rapidly and out of proportion to linear growth than did predominantly breastfed infants. These differences were attributable to greater accretion of lean mass, rather than fat mass. Any later obesity risk associated with infant feeding does not appear to be explained by differential adiposity gains in infancy.

Keywords: adiposity; body composition; breastfeeding; breastmilk; formula; growth; infant; obesity.

FIGURE 1

Flow diagram of study participants.

FIGURE 2

Trajectories of z scores for infant weight (A), BMI (B), and length (C) in formula-fed and breastfed infants. Results are displayed as estimated mean z scores ± SEMs from repeated-measures ANOVA adjusted for sex, gestational age, race/ethnicity, maternal education level, insurance type (public or no insurance, private insurance), study site, and maternal BMI. Weight and BMI z scores of formula-fed infants increased progressively over time, whereas they remained consistent in breastfed infants. These trajectories in weight and BMI z scores were statistically different between feeding groups (P < 0.001 and P = 0.02, respectively) whereas length z score trajectories were not (P = 0.16).

FIGURE 3

Trajectories of infant lean mass (A), fat mass (B), and body fat percentage (C) in formula-fed and breastfed infants. Results are displayed as estimated means ± SEMs from repeated-measures ANOVA adjusted for sex, gestational age, race/ethnicity, maternal education level, insurance type (public or no insurance, private insurance), study site, and maternal BMI. Formula-fed infants gained significantly more lean mass than did breastfed infants (P < 0.001), although fat mass and body fat percentages were similar between groups (P = 0.57 and P = 0.61, respectively).