The introduction of complementary foods and the development of overweight

There is a variety of evidence concerning age at weaning and the development of overweight. A number of studies have concluded that the age of introduction of complementary food has no effect on the risk of obesity in infancy and childhood (Burdette, Whitaker, Hall, & Daniels, 2006; Kramer, 1981; Lanigan et al., 2001; Mehta, Specker, Bartholmey, Giddnes & Ho, 1998; Maffeis, Micciolo, Must, Zaffanello, & Pinelli, 1994; Morgan et al., 2004; Reilly et al., 2005). However, a Scottish study, which identified no relationship between the timing of the introduction of complementary foods and weight at age 2 years (Forsyth, Ogston, Clark, Florey, & Howie, 1993), found that children who had started complementary foods before 15 weeks had higher weight and body fat at 7 years than those starting complementary feeding later (Wilson et al., 1998). As the increased weight and body fat was not evident at 2 years of age this may have been a programming effect (EFSA, 2009), programming referring to the concept that an insult or stimulus applied at a critical or sensitive period may have long term effects on the structure or function of an organ, system or organism (EFSA, 2009). Seach, Dharmage, Lowe, and Dixon (2010) reported that the delayed introduction of solids was associated with reduced odds of childhood overweight in ten year old Australian children and Schack-Nielsen, Sørensen, Mortensen and Michaelsen (2010) found that although there was no association with overweight in childhood, the earlier introduction of solids was associated with a higher risk of overweight at aged 42 years. Conversely, in a six and a half year follow-up of infants who had been exclusively breast fed for six months, compared to those who had been exclusively breast fed until three months, the six month group had higher fatness indices (Kramer et al., 2009). The authors speculated that maybe faster growing children, who are likely to become fatter, were breast fed for longer because mothers were confident that their milk was providing sufficient nutrition, although there is evidence that faster growing infants are given solids earlier (Fewtrell, et al., 2011).

When the EFSA Panel examined the evidence about complementary feeding and the development of overweight, they concluded that, at that time (2009), there was insufficient evidence to show that the age of introduction of complementary foods had an impact on the development of obesity. There has been some new evidence, such as the studies by Schack-Neilsen et al. (2010) and Seach et al. (2010) detailed above. However, a subsequent systematic review of the association between age at introduction of solid foods and obesity in infancy and childhood found that there was

no clear association (Moorcroft, Marshall, & McCormick, 2011). The EFSA Panel pointed out, however, that when examining the evidence concerning the introduction of complementary feeding and overweight, it was necessary also to consider studies which have found a significant positive association between high growth rates in infancy and obesity. This is because an association between earlier weaning and higher growth rates has been suggested. Baker et al. (2004) found that infants weaned before 16 weeks gained significantly more weight during their first year. In addition, a study in Ireland reported that infants who were weaned before the age of four months were heavier at seven and 14 months than those weaned later and gained more weight between eight weeks and 14 months (Sloan, Gildea, Stewart, Sneddon, & Iwaniec, 2008).

However, conflicting findings have been reported. Two randomised intervention studies have demonstrated no significant improvement in growth from introducing complementary foods at four months compared to exclusive breastfeeding to six months (Cohen, Brown, Dewey, Canahuati, & Landa Rivera, 1994; Dewey, Cohen, Brown, & Landa Rivera, 1999), although Foote and Marriott (2003) state that the sample size in these studies was small. To explain these findings, there is evidence that infants between the ages of four and six months will decrease the amount of breast milk they drink if solids are introduced into their diet, therefore maintaining their energy intake before and after supplementation and resulting in there being no weight or length advantage of the introduction of solids before six months (Kramer & Kakuma, 2002).

In a study of 1,600 infants from five prospective randomised trials conducted in the UK between 1993 and 1997, Morgan et al. (2004) found that infants who received solids at or before 12 weeks of age were heavier at 12 weeks of age. This had been reported previously. However, they showed slower gain in weight, length and head circumference between 12 weeks and 18 months so that by 18 months of age there were no significant differences in size between the two groups. They concluded that: the effects of introducing solids before or after 12 weeks on growth and health outcomes during infancy were limited; larger infants are more likely to be given solids by 12 weeks; and the introduction of solids before 12 weeks does not result in accelerated growth, at least in infancy. Similarly, Wilson et al. (1998) reported increased body weight and body fatness in children who received solids before 15 weeks, although there was no apparent effect on weight in two year follow up and Mehta et al. (1998) found no differences in weight gain up to one year of age

according to the timing of the introduction of solid foods. However, Morgan et al. (2004) comment that such findings do not preclude the later emergence of programmed effects.