The World Health Organization recommends that babies are exclusively breastfed until the age of 6 months, at which point the introduction of complementary foods should occur (weaning). An extensive literature suggests that infant feeding practices may determine long-term metabolic health in children, with effects running through to adulthood. In particular, breastfeeding has been identified as being protective against childhood obesity. Although this literature has been subject to robust criticism on the basis of confounding factors, the balance of opinion is that breastfeeding is beneficial for long-term health.
With respect to weaning, the literature is less robust and there are limited studies that consider the impact of weaning upon long-term health. Using funding from the Feeding for Life Foundation, we performed two systematic reviews of the literature to address separate questions related to the timing of weaning and the types of food used in weaning and subsequent obesity during childhood.
Our first study, including 10 reports, considered the impact of different types of weaning foods. Some association was found between high protein intakes at 2–12 months of age and higher body mass index (BMI) or body fatness in childhood, but this was not the case in all studies. Higher energy intake during complementary feeding was associated with higher BMI in childhood. Adherence to dietary guidelines during weaning was associated with a higher lean mass, but consuming specific foods or food groups made no difference to children’s BMI. We concluded that high intakes of energy and protein, particularly dairy protein, in infancy could be associated with an increase in BMI and body fatness, but further research is needed to establish the nature of the relationship.
The second review evaluated whether weaning earlier than 6 months was detrimental in terms of the later adiposity of infants. From 23 included studies we noted that there was no clear association between the timing of the introduction of complementary foods and childhood overweight or obesity. There was some evidence to suggest that very early introduction (at or before 4 months), rather than at 4–6 months or >6 months, may increase the risk of childhood overweight.