Does breastfeeding protect against later obesity risk? A discussion of recent publications
 

One of the driving forces behind the EU Childhood Obesity Programme was a seminal publication looking at obesity levels in children according to whether they had been breast or formula fed. Von Kries et al (1999), in a retrospective study, found a significantly protective effect of breastfeeding after adjusting for potential confounding factors in more than 9000 Bavarian children aged 5-6y. The prevalence of obesity in children who had never been breastfed was 1.6 fold higher than in previously breastfed children. Moreover, a clear dose-response effect was identified for the duration of breastfeeding. Three years later, Toschke et al (2002) published another retrospective study, which showed a protective effect of breastfeeding on more than 33,000 children aged 6 to 14y from the Czech Republic. Nevertheless, the differences were relatively small after adjusting for potential confounding factors.

However in October 2003, two papers were published in the same issue of the British Medical Journal, which cast doubt upon the consistency of these earlier findings. Victora et al (2003) studied 2,200 Brazilian boys, now age 18y, and previously enrolled in a birth cohort study. Although a significant trend in decreasing obesity with increasing duration of predominant breastfeeding was seen, there was no relationship with other measures of adiposity and a significant reduction in obesity was only seen in boys breast fed for 3 to 5 months. The authors concluded that breastfeeding has no marked protective effect against adolescent adiposity. In the second paper, Li et al (2003) found no significant effect of breastfeeding on obesity in the offspring of the 1958 British Birth cohort (over 2,600 British children aged between 4 and 18 years).

In an accompanying editorial, Clifford (2003) suggested that the explanation for the contradictory findings may be that all the studies 'are observational and therefore subject to several caveats'. When observational studies are inconclusive, only a randomised controlled trial (RCT) is able to prove a causal link, but an RCT of breast milk versus formula milk would be unethical, given the undoubted benefits of breastfeeding. The EU Childhood Obesity Programme is a randomised trial of two different formulas with a breastfeeding cohort alongside. It will follow the growth of breast and formula fed babies over 8 years and will not only monitor their subsequent obesity risk but will also explore one potential mechanism for any protective effect of breast feeding by using formula with different protein/fat ratios.

Although still subject to possible confounding, it is hoped that the quality of data that will come out of this study will allow any relationship between breastfeeding and childhood obesity to be clearly seen. Even if the effects are small, given the increasing frequency of childhood obesity, the public health benefits would still be huge.

 

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