Research suggests that the nutrition received by the foetus during particular periods of growth, and by the infant postnatally, are important determinants of future metabolic abnormalities. The association between infant or foetal nutrition and obesity and type 2 diabetes is fairly well established, and suggests that nutrition during sensitive periods of growth is vital for correct endocrine development. Breastfeeding versus formula feeding has therefore become of interest to the nutritional sciences because it represents a time window when nutritional influence may be at their greatest. The insulin disposition index is a quantitative measure that describes the relationship between β-cell sensitivity and insulin sensitivity. While the mechanisms are not known, some evidence now suggests that formula feeding can detrimentally alter the β-cell and insulin sensitivity relative to that of breast feeding. Efforts have therefore been made to measure the insulin function of children who were both breast and formula fed.
For example, researchers1 have investigated the association between the type of feeding in early infancy and insulin metabolism in 8 year old overweight and obese children. A 120-minute oral glucose tolerance test was used to assess insulin function in 350 overweight and 33 normal-weight children (controls) who had been exclusively breast or formula fed as infants. The results showed that insulin sensitivity was significantly lower in the formula fed overweight children when compared to the breastfed overweight children, despite having similar adiposity levels. The researchers reported that the formula fed children compensated for the reduced insulin sensitivity by secreting more insulin, which resulted in a similar insulin disposition index between groups. In addition, infants that were formula fed were significantly more likely to catch up body weight and size with accelerated growth between 6 and 12 months of life if born small for gestational age.
These results suggest that breast feeding in early infancy is associated with improved insulin sensitivity in childhood. The interesting finding of this study was that formula fed children who are overweight, but have the same levels of adiposity as breast fed children, compensate for deleterious insulin sensitivity by secreting more insulin. Irrespective of feeding habits during infancy, children appear to be able to maintain the same insulin disposition despite differences in insulin sensitivity. This may explain why type 2 diabetes does not manifest until later adult life, when this over-compensatory mechanisms has started to dysfunction. Growth hormone, insulin, growth factors, adrenal steroids, triiodothyronine and tetraiodothyronine are all found in breast milk and are all known to influence pancreatic β-cell function. The improved β-cell function could also be explained by the presence of docosahexanoic acid (DHA, C22:6 (n-3)) and higher protein content when compared to formula milk.
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