Growth & Development: Growth of Breastfed Infants in the Developed World

The DARLING Study

Kay Dewey, Ph.D. and her associates performed the DARLING Study (Davis Area Research on Lactation in Infant Nutrition and Growth) in Davis California in the early 90's ( Dewey, 1992 ).

The study compared two groups of infants, one that was breast-fed for a year, and another that was largely formula fed.

Characteristics of the study participants

1. (breastfeeding group) Women who intended to breast-feed their infants for twelve months and add foods at four to six months of age.
2. (formula fed group) Women who would breast feed less than 6 weeks or not at all and add foods at 4-6 months.
3. All infants had a birth weight greater than 2500 grams.
4. From the Davis, California area.
5. An upper middle class sample population.
6. 40 to 50 infants in each group.

Monitoring interval

Growth was monitored monthly or every 2 months and nutritional intake was monitored every three months.

Results of the study

1. The groups had similar weight gain during the first 3 months.
2. The breast-fed infant’s weight gain decreased between six to twelve months of age and by one year they were leaner than the formula fed infants.
3. The length and head circumferences of infants in both groups were similar.

The PROBIT Study

*Z score is the amount of 1 S.D. above or below the 50th percentile on the NCHS growth curves

Like the infants from the United States in the Darling study, these exclusively breastfed infants were fatter at 3 months of age compared to the infants breastfed < 1 month. By 12 months the breastfed infants were slimmer than those breastfed < 1 month ( Kramer, 2002 ).

The effect of the addition of supplemental formula and cereal to continued breastfeeding was studied in this group of infants between the ages of 1 and 12 months. Infants who received both breast milk and formula between 3 and 12 months of age were slightly heavier from 6-12 months of age then were infants who had received only breast milk as their source of milk. The addition of cereal between 3 and 6 months of age was associated with lower weight at 6 months of age. This suggests that cereal replaces breast milk in the diet, and is not being added to breast milk ( Kramer, 2004 ).

Kramer and his co-workers re-evaluated 13,889 of the 17,046 children (81.5%) enrolled in the PROBIT study when they were 6.5 years of age. They compared the children in the experimental group of whom 43.3% were exclusively breastfed for 3 months to the children in the control group where 6.4% were exclusively breastfed for the first 3 months of life. There was no difference in height, BMI, waist circumference, or midupper arm circumference between the 2 groups. This study supports the concept that breastfed infants grow differently from infants fed formula in the first year of life, but the 2 groups grow similarly later in life ( Kramer, 2007 ).

Growth of Breast Fed SGA Infants

Lucas and co-workers in England evaluated the growth of Small for Gestational Age (SGA) infants who were breast fed compared to a group of formula fed SGA infants. They found that the breast fed infants had better catch-up growth in weight, length and head circumference in the first three months of life. The breast fed infants remained larger in all three parameters at 12 months of age, but had no further catch-up growth after three months of age ( Lucas, 1997 ).