A large body of evidence suggests that breastfeeding is superior to formula feeding. The reason for this is not fully understood, but a number of nutritional differences exist between breastmilk and formula milk that could explain the discrepancy. Of particular note is the fact that breast milk contains high amounts of essential fatty acids that are needed for normal infant growth, whereas in formula milk these are not present because they would considerably shorten the shelf life of the product. Such fatty acids are prone to rancidity due to their highly reduced state which makes them particularly sensitive to reaction with oxygen. Such essential fatty acids, particularly docosahexaenoic acid (DHA, C22:6 (n-3)) are required for proper brain development, but a number of other cell regulatory roles are known. Studies have suggested that breastfed infants are less likely to develop western lifestyle diseases in later life, and in particular may have a significant reduced risk of weight gain and obesity.
A number of countries have seen recent falls in the rates of breastfeeding, and it has been suggested that this may be linked to the increasing rates of obesity. For example, in Mexico, breastfeeding rates fell between 1999 and 2012 but at the same time obesity levels in young children increased. Some have therefore claimed that breastfeeding may have important anti-obesogenic functions in human development. In one study1, in Mexico, infants that were not breastfed up to 3 months, or were only partially breastfed, had significantly higher body mass indices at 4 years compared to those that were breastfed. The non-breastfed infants also had significantly higher blood cholesterol levels compared to breastfed infants, and this may be indicative of metabolic syndrome. That insulin resistance was inversely associated with breastfeeding in the Mexicans adds weight to the argument that formula feeding may decrease the sensitivity of the insulin system, thereby increasing the risk of weight gain.
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