Childhood obesity

Overweight and obesity levels are rising in both children and adults^{(e.g. 1)}. Identifying key periods of the lifespan during which overweight and obesity are likely to develop is thus essential to optimize prevention strategies. The period following birth is a crucial time for obesity development⁽²⁾ and could be a target for prevention since there is a clear opportunity to modify feeding practices, influence appetite regulation and shape early eating behaviours.

Rapid infant weight gain

Weight gain velocity is a risk factor in the development of overweight and obesity in later life^(3-6). Children who gain weight rapidly in the first months of life are more likely to be obese in childhood than those who gain weight along the predicted trajectory⁽⁶⁾. In a study of 90 Icelandic infants until age 6, weight gain from birth to 12 months as a ratio of birth weight was positively and highly correlated to BMI at age 6⁽⁷⁾. Many variables could contribute to the pattern of rapid growth in infancy, including “catch-up” growth in response to undernutrition during gestation⁽⁸⁾.

Breastfeeding may protect against rapid weight gain and lower the risk of developing overweight and obesity later in life. A comprehensive review of 61 studies concluded that initial breastfeeding protects against obesity⁽⁹⁾. The protection mechanism is as yet unclear, but there is likely to be a better match between varying energy requirements of the growing infant and breast milk than formula. Breastfeeding on demand allows the infant to determine meal frequency and pattern which may entrain the development of the early appetite system to internal cues (hunger and satiety) rather than the mother determining meal pattern and size⁽¹⁰⁾. Mothers’ attitudes, beliefs and concerns influence feeding patterns: in one study high maternal concern about overfeeding (significantly higher in obese mothers) was associated with a higher fat mass in 5-year-old children compared to low concern⁽¹¹⁾. Thus, maternal weight status confers both a biological endowment and shapes behaviour towards the infant including method and pattern of feeding.

Early weaning increases risk of overweight and obesity

Infants who are weaned early (at or before 4 months) appear to have a higher risk of overweight and obesity later in childhood. Ong et al (2006) examined the relationship between dietary intake at age 4 months and weight gain in the first 5 years as well as body weight at age 5. They found significantly higher total energy intakes in those weaned at 1 – 2 months compared to those weaned at 4 months and later with an associated greater weight gain. No such effects were found for breastfed infants(3).
What influences the timing and introduction of solid foods? Evidence from interviews with mothers^{(12, 13)} suggests that early introduction of solid foods was associated with social deprivation, mothers’ perceptions of infant needs (including having a “hungry” baby), free samples of solids by manufacturers and lack of support to extend the period of breast or bottle feeding.

It is interesting to speculate on how mothers identify “hungry” babies. These infants may have a strong drive to feed, as part of their “catch-up” growth if they are small. A prospective study of 923 infants found that the median age for introducing solids was 3.5 months and the greatest independent predictors of early weaning included rapid weight gain to age 6 weeks, lower socioeconomic status (SES), parental perception of a hungry baby, and feeding mode⁽¹⁴⁾. Thus, rapid infant weight gain is associated with early weaning, perhaps because infants are perceived as “hungry”, and that solid foods are required to meet infant need. The causal direction of this relationship is not yet clear. Is it that mothers respond to hungry babies who need to “catch-up” by feeding them more and weaning them early or do mothers perceive distress or discomfort as “hunger” and respond by feeding to comfort them? Mothers’ perceptions of need can be associated with body size.  Research on African American mothers found that perception of babies as small increased early introduction of non-milk solid foods⁽¹⁵⁾. Social groups vary in their perceptions of acceptable body size for babies, thus, African American mothers report a greater acceptance of large body size in their babies and few see this as a potential health risk ⁽¹⁶⁾. Similarly, some mothers believe that a “chubby baby is a healthy baby”. Preference for varying body size was examined in 50 mothers: older, breast-feeding mothers from higher SES backgrounds preferred leaner infants ⁽¹⁷⁾. The mother’s perception that her baby is small, the belief that a bigger baby is better and concerns about having a “hungry” baby are all likely to contribute to feeding practice, including decisions about breast or bottle feeding, early weaning and potentially to overfeeding.

Preventing childhood obesity

Infant feeding practices play an important role in determining risk for overweight and obesity later in life. However, as children grow there are many different issues which converge to amplify that risk, such as physical activity, television viewing, energy and nutrient intake.

Six key strategies have been identified to prevent overweight in children, namely: breastfeeding, increasing physical activity, reducing TV viewing, increasing fruit and vegetable intake, reducing sugarsweetened drink intake and decreasing portion sizes⁽¹⁸⁾. However, a stronger evidence base is needed to understand the converging factors which increase risk of overweight and obesity and the appropriate interventions (e.g. individual or population-based) which tackle weight gain. Ideally, given the current pandemic of overweight and obesity among children, it will be through both personalised nutrition and activity interventions together with effective public health policies that childhood obesity will be prevented.