New research centring on the protein adiponectin, secreted by fat cells and affects how the body processes sugars and lipids, suggests that its presence in large quantities in breast milk could be the reason for the reduced obesity risk.
Adiponectin is thought to be involved in the metabolic syndrome, which includes insulin resistance, obesity, type 2 diabetes and coronary artery disease and occurs in 20-25 per cent of adults. Higher levels of adiponectin have been associated with lower levels of these diseases.
Researchers at Cincinnati Children's Hospital Medical Center in the US wanted to gauge whether adiponectin was present in human milk, and whether the protein could have an influence over the metabolic 'programming' of infants by reducing the preponderance towards adiposity or 'fatness'.
The researchers analysed samples of human milk collected from anonymous donor mothers as part of the Research Human Milk Bank at the medical centre and found levels of adiponectin that were "quite high - higher than many proteins found in human milk," according to Dr Lisa Martin, the study's lead author.
"This study is an important first step in developing molecular research focused on understanding the relationship between human milk constituents and later metabolism. Exposures early in life, during the period of extreme growth and development, may have an impact on adult disease," she added.
The researchers also confirmed the presence of leptin in human milk, providing further evidence that breastfeeding could affect adiposity. Leptin is another protein produced by fat which is thought to play an important role in the regulation of body fat. Leptin is a satiety hormone, involved in the state of being 'full'.
Adiponectin levels, however, are substantially greater than leptin in human milk, according to Dr Martin, a researcher in the Center for Epidemiology and Biostatistics at Cincinnati Children's and in the Division of Human Genetics. "Whether the greater quantity of adiponectin has biological significance remains to be seen," she added.
The research from the US supports the growing body of evidence in Europe linking breast feeding to a lower risk of obesity. Last year, for example, the German Federal Institute for Risk Assessment (BfR), which advises the Government on consumer health and food safety, began touting the benefits of breastmilk as a 'super cocktail' that protects against obesity and offers many other health benefits.
One in five children in Germany are obese, according to BfG, while a recent Datamonitor report suggested that 30 per cent of British five- to nine-year-olds are overweight or obese. Some 16 per cent of US children are considered as obese.
The numbers of overweight children are growing in several developed nations, putting them at greater risk of developing nutrition-related diseases such as type 2 diabetes. A study last year found that infants who gain weight quickly in the first few months after birth may be more likely to be obese as young adults.