Early-Life Nutrition and Stable Isotope Techniques

Both fetal and early postnatal life are periods of rapid growth and development. Alterations in growth during these periods of life are associated with impaired health outcomes. Feeding practices during early life can modify infant growth patterns. Stable isotope techniques with nonradioactive isotopes, such as deuterium oxide or 18O-labeled water, are of great value for studies on infant nutrition, especially regarding measurements of milk intake in (exclusively) breast-fed and formula-fed infants, and determination of body composition through total body water. Stable isotopes can also be used for determination of the optimal composition of infant formula, based on bioavailability of numerous components of infant formula combined with infant requirements. Other stable isotope applications regarding infant nutrition include verification of food safety of infant formula, by ensuring product quality and identifying possible contamination, and comparison of cholesterol biosynthesis between formula-fed and breast-fed infants. The use of stable isotopes in infants is safe and accurate provided that researchers are aware of limitations and procedures are performed strictly. Within this chapter, we describe the background and the application of the deuterium dilution technique to measure milk intake in both breast-fed and formula-fed infants, including methods and calculations. Furthermore, we describe additional applications of stable isotopes regarding infant nutrition, the limitations of working with stable isotopes, and the practical issues.