New Study: Exclusive Breastfeeding Can Support Infant Growth to 6 Months of Age
A new study published this week in the journal Pediatrics found that exclusive breastfeeding up to six months provides enough calories for infants.
Quick and Dirty Summary:
This study addressed two common concerns about breastfeeding: 1) Many moms simply can’t produce enough milk for their babies; and 2) Exclusive breastfeeding, while adequate in younger infants, may not provide enough calories for babies up to 6 months of age. The data from this study indicate that when moms are given breastfeeding support, milk production is not a limiting factor and provides enough calories for normal growth, even in 6-month-old infants. However, this study was small and had several limitations (which I will discuss).
How was this study conducted?
This was a longitudinal study of 50 mothers and their infants in Glasgow, Scotland. All of these mothers intended to exclusively breastfeed (EBF) for at least 6 months and were recruited from breastfeeding support groups, so we can presume that they were already set up to succeed with breastfeeding. EBF is defined by the World Health Organization (WHO) and in this study as giving the infant only breast milk for nutrition (no solids or formula), with oral rehydration, vitamins, minerals, or medicines allowed as needed. 60 mothers were recruited,but only 50 were still EBF at the first assessment around 15 weeks of age. Assessments included measurements of infant growth, milk intake, total energy intake, and milk energy content. Mothers also completed questionnaires and infant behavior diaries in order quantify the number of feedings and total time spent nursing. These measurements were all repeated at 25 weeks of age (6 months). At this second time-point, 3 mothers had dropped out of the study and 41 mothers were still EBF. The remaining 6 mothers had begun feeding their babies some solid foods.
How, you might ask, did the researchers manage to measure milk intake in nursing babies? Excellent question. They used a technique called the doubly-labeled water method, which involves feeding the baby a tiny and safe dose of stable isotope-labeled water (2H218O) and then collecting samples of their pee (which is easy enough to do when you change a diaper) to measure how long it takes those isotopes to come out. Then they did a bunch of calculations. Really. Trust me when I tell you that this method is safe, non-invasive, and pretty much the best way to measure milk intake in nursing babies. I’ve actually had a little experience (in a previous life) using this method in nursing bottle-nosed dolphins.
What are the most important findings of the study?
–The exclusively breast fed infants in this study grew just fine, right in line with the WHO Child Growth Standards. EBF to 6 months didn’t set them back in their growth curves.
-Milk intake was significantly higher at 25 weeks compared with 15 weeks (997 vs. 923 grams; P=0.001), showing that milk production increased to meet the increasing demands of the infant. Milk energy content (as in calories per liter) did not change between time points.
-Moms reported breastfeeding 8-9 times per day at both 15 and 25 weeks, but time spent feeding decreased from 173 minutes per day at 15 weeks to 140 minutes at 25 weeks. That means that at 25 weeks of age, babies were drinking more milk but doing so more efficiently than at 15 weeks. No surprise there.
-There was no difference in infant weight or milk intake at 25 weeks between the EBF infants and the 6 that had started solid foods. The moms of these babies said they started solids because their babies seemed ready.
What can we conclude from this study?
The study shows that in most women with good breastfeeding support, infant milk intake is sufficient to support normal growth with EBF for 6 months.
The authors of the study assert that their findings support the recommendation that all babies should be EBF for the first 6 months, but there are some problems with jumping to that conclusion…
What are the limitations of the study?
-10 of the 60 moms initially enrolled in the study were not still exclusively breastfeeding at 15 weeks, and the study authors don’t tell us what happened to those 10 women. Did they stop breastfeeding or supplement with formula because of a fear, real or not, that they weren’t producing enough milk? We just don’t know.
-The mothers in this study were older (mean age 33) and more affluent than the average mom. They were highly motivated to exclusively breastfeed and had good support to do so. Just guessing, but this type of mom is also more likely to take good care of herself and have support at home to do that. All of those factors might impact her breastfeeding success.
-The 6 babies that were started on complementary foods prior to 6 months had similar caloric intake from milk as the EBF babies. These babies were also getting some calories from food, but how much was not reported in the study. It is possible that these babies were truly ready for solids before 6 months and needed the added energy from solids, in addition to breastmilk. The authors don’t address this question.
-This study only looked at calories from milk intake. It doesn’t consider micronutrients such as iron and zinc that may become limiting at this age without the addition of some solid foods in the diet.
This study shows that exclusive breastfeeding to 6 months can provide enough energy to support normal growth in babies. However, this was a study of highly-motivated women with great support for breastfeeding. It does not investigate why 10 women dropped out of the study or if the babies consuming complementary foods actually needed the calories from that food. Due to these limitations, the results of this study may not apply to the general population.
It is easy to over-simplify the results of a study like this, but when we really look at the data, we find that it just isn’t that simple. Unfortunately, most science isn’t.