Breast feeding does not protect against overweight and obesity in later life, as previously believed, suggest researchers in two studies in this week's British Medical Journal.
Childhood obesity has been climbing rapidly and some theories linked the reduction in breast feeding to this trend. It had been thought that the different compositions of breast milk and milk substitutes may trigger differing hormonal reactions in the breastfed child and put their stamp on his metabolism. Other theories suggest that the breastfed infant drinks until he is full whereas the bottle-fed baby aims to finish the bottle and is therefore brought up to eat more than he needs.
However new research suggests that breast feeding may not in fact help reduce the numbers of obese. The first study followed 2,250 male Brazilians for 18 years, after collecting detailed breast feeding information in early childhood.
The team from the Universidade Federal de Pelotas in Brazil said that results were mostly negative, showing that duration of breast feeding had no association with several measures including weight and body composition. After adjusting for factors such as physical activity, diet, and smoking, two significant associations remained, but these should be interpreted with caution, say the authors.
The second study involved 2,631 British children, for whom data on duration of breast feeding, body mass index, and confounding factors (such as birth weight, mother's smoking during pregnancy, parental body mass index, and social class) were available.
The researchers from the Institute of Child Health in London found no evidence that breast feeding influenced body mass index or obesity, and adjustment for confounding factors did not alter these findings.
The authors stressed that regardless of the role of breast feeding may have in preventing obesity, the continued protection, promotion, and support of breast feeding remains a major public health priority. However evidence for an important beneficial effect on obesity is still equivocal, they concluded.