Breast-fed and formula-fed infants both face nutritional challenges at the time of weaning, at 4-6 months of age. Because breast milk is not a good source of iron, iron-rich weaning foods are important to prevent iron deficiency. During weaning, formula-fed infants may face a deficiency of docosahexaenoic acid (DHA), an n-3 fatty acid essential for the growth and functional development of the brain that, until recently, was not added to most infant formulas.
Egg yolks are rich sources of both heme iron and DHA and have a soft texture suitable for weaning infants. Publishing in the American Journal of Clinical Nutrition, Makrides et al. studied the nutritional value of including two different varieties of egg yolks as weaning foods for a group of breast-fed and formula-fed infants and found that egg yolks provided advantages to both groups, with no negative effects on cholesterol concentrations.
The 137 mother-infant pairs in the study were recruited through immunization clinics in the Adelaide, Australia vicinity, and the 6-month-old infants were randomly assigned to receive either no dietary intervention (control), regular eggs, or eggs that had been enriched by feeding hens diets rich in n-3 fatty acids.
At 6 months and 12 months of age, infant blood samples were obtained for measurement of DHA in red blood cells, iron status, and plasma cholesterol. In both breast-fed and formula-fed groups, infants who consumed n-3 fatty acid enriched egg yolks had 30-40% greater red cell membrane DHA levels than those fed regular egg yolks. There was no effect of n-3 fatty acid enriched egg yolks on plasma cholesterol, but plasma iron levels were increased.
The advantages of egg yolks for weaning purposes include their practicality and palatability as a food for infants, a modest improvement in iron status, and--in the case of n-3 enriched eggs--a means of increasing dietary DHA without negative effects on cholesterol levels.
The authors suggest that future research in the field be directed toward determining the physiologic benefits of enhancing DHA in the latter part of infancy.