Dietary energy intake at the age of 4 months predicts postnatal weight gain and childhood body mass index

The impact of early nutrition in premature infants on later childhood insulin sensitivity and growth

OBJECTIVES

Children born prematurely have decreased insulin sensitivity. The etiology of this insulin resistance is unknown. The aim of this study was to evaluate infant nutrition and its influence on insulin sensitivity and postnatal growth in children born < or = 32 weeks' gestation.

METHODS

A total of 56 healthy, developmentally normal, prepubertal children, aged 4 to 10 years were recruited. Thirty-seven were born < or = 32 weeks' gestation, and 19 were control subjects born at term with a birth weight > 10th percentile. Insulin sensitivity (10(-4) min(-1) microU/mL) was calculated from a 90-minute frequently sampled intravenous glucose tolerance test. Perinatal, nutritional, and growth data were obtained retrospectively from both neonatal and early infancy records in the premature cohort.

RESULTS

Children born prematurely had decreased insulin sensitivity when compared with those born at term (13.8 vs 30.6). Neonatal nutrition was not correlated with insulin sensitivity; however, all of the infants had inadequate protein in the first month followed by excessive fat intake thereafter. Premature children with greater weight gain had lower insulin sensitivity. Higher carbohydrate intake in the first month of life was associated with greater weight gain from birth. No relationship was seen between weight gain and either protein or lipid intake.

CONCLUSIONS

Prematurely born children are insulin resistant and have suboptimal neonatal nutrition. Greater childhood weight gain magnifies this reduction in insulin sensitivity and seems to be associated with early nutrition. We speculate that a high carbohydrate neonatal diet may lead to greater weight gain and a greater reduction in insulin sensitivity in this group.

Differences in weaning practice, food and nutrient intake between breast- and formula-fed 4-month-old infants in England

BACKGROUND

Breastfed infants may grow more slowly in the second half of infancy than formula-fed infants, differences in weaning practice may contribute.

METHODS

Dietary intakes of 4-month-old infants have been investigated cross-sectionally. Diet was assessed using a structured 1-day un-weighed dietary record in 852 white singletons (72% of those invited) from a random sub-sample of infants taking part in Avon Longitudinal Study of Parents and Children. Nutrient intakes of formula-fed infants were compared by sex and with UK reference values. Estimated mean energy and nutrient intakes, mean bodyweight and daily quantities of food consumed were compared by weaning practice.

RESULTS

In formula-fed infants mean energy intakes and intakes of most nutrients were adequate. There were significant differences in intakes of most nutrients by weaning practice; however, mean energy intake and body weight of breastfed infants was similar to formula-fed infants. Infants given formula milk were less likely to consume vegetables and fruit, and more likely to consume commercial infant drinks, compared with infants who were breastfed. In breastfed infants breast milk intake was lower if solids were given (905 g versus 818 g; P = 0.01); however, nutrient intake was not compromised. In formula-fed infants milk intake was not different in those having solids compared to those having milk only (810 g versus 795 g; P = 0.649).

CONCLUSIONS

Differences in weaning practice and patterns of food consumption were seen between breast- and formula-fed infants, these may contribute to later growth differences.

Rapid infancy weight gain and subsequent obesity: systematic reviews and hopeful suggestions

In a systematic review, we identified 21 separate studies with data on the association between rapid infancy weight gain, up to age 2 y, and subsequent obesity risk. Uniformly all studies reported significant positive associations. We transformed the reported effect sizes to a standard infancy weight gain exposure, and found that further differences in study design accounted for much of the variation in risk. An accompanying paper by Melinda Yeung reminds us that there are benefits of postnatal catch-up growth in certain populations, and suggests that genetic and nutritional factors could moderate the unhealthy translation of rapid infancy weight gain to visceral fat and insulin resistance. Further evidence is needed, and we will need to rigorously test the benefits and risks of any interventions. However, the concept of "healthy" rapid catch-up infancy growth is an attractive prospect.

CONCLUSION

Rapid infancy weight gain is consistently associated with increased subsequent obesity risk, but the predictive ability of different weight gain cut-offs needs to be tested.

Early and late weight gain and the timing of puberty

Nutrition is an important regulator of the tempo of growth and obesity is usually associated with tall childhood stature and earlier pubertal development. Several longitudinal studies have demonstrated that timing of puberty is most closely linked to infancy weight gain: suggesting an early window for programming of growth and development. Earlier puberty in the UK MRC 1946 birth cohort was related to smaller size at birth and rapid growth between 0 and 2 years. Rapid early weight gain leads to taller childhood stature and higher insulin-like growth factor I (IGF-I) levels, possibly through early induction of growth hormone (GH) receptor numbers, and such children are also at risk of childhood obesity. In the Avon Longitudinal Study of Parents and Children, rapid infancy weight gain was associated with increased risk of obesity at 5 and 8 years, with evidence of insulin resistance, exaggerated adrenarche and reduced levels of sex hormone binding globulin (SHBG). Potentially the elevated IGF-I and adrenal androgen levels, increased aromatase activity and increased 'free' sex steroid levels consequent to lower SHBG levels could all promote activity of the GnRH pulse generator. In addition obese children have higher leptin levels, a proven permissive factor in initiating LH pulsatility. Obesity could also affect the rate of progression through puberty as nutrition and SHBG may act respectively as an accelerator and brake on peripheral sex steroid action. Early weight gain and early pubertal development might also be associated with loss of the pubertal growth spurt perhaps through obesity-related suppression of GH secretion. Trans-generational recurrence of low birth weight, early catch-up weight gain, earlier menarche, and shorter adult stature have been observed in women, and could contribute to the strong heritability in age at menarche.

Size at Birth, Postnatal Growth and Risk of Obesity

Epidemiological studies over the last 15 years have shown that size at birth, early postnatal catch-up growth and excess childhood weight gain are associated with an increased risk of adult cardiovascular disease and type 2 diabetes. At the same time, rising rates of obesity and overweight in children, even at pre-school ages, have shifted efforts towards the identification of very early factors that predict risk of subsequent obesity, which may allow early targeted interventions. Overall, higher birth weight is positively associated with subsequent greater body mass index in childhood and later life; however, the relationship is complex. Higher birth weight is associated with greater subsequent lean mass, rather than fat mass. In contrast, lower birth weight is associated with a subsequent higher ratio of fat mass to lean mass, and greater central fat and insulin resistance. This paradoxical effect of lower birth weight is at least partly explained by the observation that infants who have been growth restrained in utero tend to gain weight more rapidly, or 'catch up', during the early postnatal period, which leads to increased central fat deposition. There is still debate as to whether there are critical early periods for obesity: does excess weight gain during infancy, childhood or even very early neonatal life have a greater impact on long-term fat deposition and insulin resistance? Early identification of childhood obesity risk will be aided by identification of maternal and fetal genes that regulate fetal nutrition and growth, and postnatal genes that regulate appetite, energy expenditure and the partitioning of energy intake into fat or lean tissue growth.