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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.

My take: 

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.

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7 Comments
  1. I weaned Enoch when he was 7 months old not because I didn't have milk but I felt I was done with BF. Enoch didn't take a bottle so it was hard for me to not be able to leave him with anybody else without him being starved. I do feel guilty sometimes for not bf Enoch for a year but I think maybe 6-7 months is my limit, I might carry it out with all my babies. I notice that when I'm supper tired I tend to make less milk. I have lower milk supply later afternoons than early mornings. It's probably true with most people. I can see that why a good support group can really influence breastfeeding.

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    September 22, 2011
  2. Hi Sharon,I really think your question about the benefits of breastfeeding beyond 6-7 months is a good one. I have it on my list of things to research. I know plenty of moms that have weaned around that time, and I'm guessing that it is most important to BF for those first 6 months. I know there are some benefits of going longer, but I think every mom has to weigh the decision for herself. I think if BF has become a burden to you and weaning allows you to be a better mom the rest of the time, that is a perfectly valid reason to choose to wean! And Enoch is clearly a very healthy little boy who benefited from your milk for those 7 months! Now you are on to the next one, which makes you a trooper! Hope you are doing well and not super tired all the time:)

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    September 22, 2011
  3. ScienceofMom #

    Between the time that I imported my Blogger site (scienceofmom.blogspot.com) content over to WordPress and then got it up and ready for the public, a great discussion of this post continued. I’ve copied it over here to record it for posterity – too afraid to try an actual import for fear that it will screw up the formatting.

    Jenny F. Scientist, PhD said…
    We ended up giving Bug a little applesauce and oatmeal around 4/5 months because he was home with the spouse and would NOT NOT NOT take a bottle and there is no joy like a 4-month-old who hasn’t eaten anything for nine hours. I think we would have given him a little solid food before exactly 6 months anyways, because he was enormous (20+ pounds at 4 months) and hungry and kept trying to eat our food.

    I was like a fire hose on the milk supply, fortunately. When I pumped it looked like double heavy cream. No calorie concerns there. (See also: 20 pound 4 month old, who had gained a pound a week for three full months.)
    September 22, 2011 8:42 PM

    JLarsen said…
    Hi Alice,

    Interesting study. I wonder if the growth charts they used were based on babies who were BF or not? I’ve heard this is a concern in the US (ie the charts are based on data from formula-fed infants- true??), and the criticism is that those babies dont have the same ‘I’m full’ signals that come from hormones in milk and/or a bottle nipple allows for much faster flow and more volume per feeding. Of course, there is also the concern that formula-fed babies are more prone to obesity too, but I have no idea if *any of those concerns are supported by science. Do you know?

    I BF my child for over 2 years, and exclusively for just over 6 mo. He was absolutely not ready for solids before then. I had no supply problems and am grateful for all of that. Since I will only have one child I treasure that experience (except for the clogged ducts, episode of mastitis, etc!). Anyway, I wonder if there is also scientific support for factors that ensure a good supply. Intuitively we know stress, hydration, pumping if you work, etc are all critically important, but do we have data?

    Just wondering aloud! Great post as always.
    September 24, 2011 9:51 AM

    scienceofmom said…
    Jen – You pose a great question re the growth standards used. This study used the 2006 WHO standards, which are based on an international sample of breastfed children “raised under optimal environmental conditions.” The CDC released updated growth standards in 2000 which were based on NHANES data pooling all babies – breast and formula-fed – in their US dataset (they say about 30% breastfed up to 3 months, beyond that we’re not sure). However, the CDC now recommends that pediatricians use the WHO standards up to 2 years, because they are more likely to describe optimal growth, assuming BF provides optimal nutrition. As we know, more is not always better when it comes to infant growth. I think our Tucson pediatrician still used the CDC growth curves though. This is on my list of potential posts – comparing the different growth curves for formula vs. breastfed babies (i.e. – why did my baby fall from 95% to 15% in 6 months?!)

    I don’t know the answer to your question about factors affecting supply, but I’ll put it on my list of things to research:) I’m sure there are animal data, but these types of studies are harder to do in humans… so many factors.

    Reading Jen and Jenny’s comments above, I’m struck by how different babies can be in that 4-6 months range. Like most nutrition recommendations, it is difficult to assign a one-size-fits-all guideline. I would bet that the optimal time for solid food introduction actually varies quite a bit from baby to baby.
    September 24, 2011 10:46 AM

    JLarsen said…
    Thanks Alice! Would love to see some actual info on these topics. And thanks also for the clarification in the growth chart info. I’m sure the Amer. Acad. of Pediatrics has some sort of guidelines?

    I am always amazed at the varied experiences of different families, or even different children within the same family. Jenny had a intense sort of stress, I’m sure, in that her baby refused bottles. I remember the conflicting advice about ‘nipple confusion’ and it drove me mad- I didnt know what to do. Thank goodness Aiden took a bottle fine at daycare and once I figured out a pumping and storage system it was fine. Transitioning to solids was hard too, since A wasnt that thrilled about it, plus we were also moving him from our bed to his around that time- maybe not the greatest timing on our part.

    I think he is turning out ok despite my stumblings! 😉
    September 24, 2011 7:38 PM

    scienceofmom said…
    Jen, in November 2010 the AAP stated in a press release that they supported the switch to the WHO growth charts, but as far as I can tell, they haven’t released an actual policy statement. My guess is that some pediatricians have made the switch and others haven’t. In general, the WHO curves (BF babies) show more rapid weight gain for the first few months but then drop below the CDC curves for 6-24 months. Length is higher in the WHO curves. Maybe this will be my next post, since I have all of these papers pulled up now. Then I can give you all the citations:)

    Thanks so much for you contributions to the discussion! These babies are definitely all different, and the advice can be so confusing. I guess I’m finding that the science is not always clear either. Luckily babies do seem to tolerate our confusion, and I know A turned out just awesome!
    September 24, 2011 10:40 PM

    scienceofmom said…
    Oh, and I almost forgot. Guess who made up the US cohort in the WHO data? Babies from affluent families in Davis, CA.
    September 24, 2011 10:51 PM

    Bionic Baby Mama said…
    But if some women really don’t make enough milk for their babies (at whatever age, whether because of early low-supply concerns from anemia, etc., or later ones), aren’t they exactly the ones who would have dropped out of this cohort (or never been in it)? was there really a question whether any women can make enough milk for a 6 mo old?

    as usual, my hackles are raised by some of the language here, notably that the difference between “succeeding” or not is down to “support” and willingness only. No doubt those are important (though it’s cute how many things are elided in “support,” which sounds like it just means a good LC but also includes, as you note, class, necessity of working a job that may or may not allow you to pump, not to mention having a body that is able to pump), but surely bodies, not just minds and circumstances, can vary.
    September 25, 2011 7:24 AM

    JLarsen said…
    Ha- thats funny! Assuming the cohort data was collected no later than early 2000’s and maybe spanned to much earlier (70’s?), that means that most of those babies were probably white. They probably had a lot of vitamin D too. 😉

    Alice, I think you should consider a science-based parenting book. The ones out there suck, as I’m sure you found. I ended up skimming a bunch plus internet resources, etc. and not really finding a good one. I did like some of the stuff in the Sears books, but their potty training advice simply sucks. Also, the iconic ‘What to Expect…’ is terrible.
    September 25, 2011 9:40 AM

    scienceofmom said…
    Bionic – Yes, I totally agree re your comment about the 10 women that dropped out of the study. I think this is a major shortcoming of the study. Reading the intro to this paper, I got excited, because it sounded like they were really going to investigate the supply question, but how could they when they lost 17% of their study participants before their first measurement? By 15 weeks, those were definitely the women that might have quit BF because of supply issues. Then again, really investigating this question would be very difficult…

    My commentary about factors affecting breastfeeding success (and I don’t mean that to be equated with parenting success or feeding success) is purely speculative. I just wanted to make the point that this was a study of a small group of women not representative of the entire population of women out there who might attempt breastfeeding. I’m sure there is natural variation in a woman’s genetic potential to produce milk, as well as other nutritional and environmental factors that might contribute to production. And I think you are right to point out my bias that a more affluent mother is more likely to be successful – thanks for that. My family was dirt poor when I was a baby, though they were well-educated. My mom breastfed my brother and I without any lactation consultants, books, or even many friends (or her own mother) who breastfed. Though she believed it was the healthier way to feed us, I’m sure the cost of formula was also a factor in her “success” with breastfeeding!
    September 25, 2011 11:41 AM

    Bionic Baby Mama said…

    Oh, believe me, the cost of formula is a big reason that my son was (almost) exclusively breastfed for 6 months! (the almost is for the few ounces of formula he needed at the beginning when my milk really wasn’t enough (even the hippy LC thought the pediatrician had waited too long to tell us to supplement; it really was necessary) and for a couple of pickles and tomatoes he managed to gnaw on after 4 months. now, at 6.5 months, he is starting to really eat food. he also gets formula when i work, because i cannot pump. look: i’m defensive even though i’ve officially “succeeded”! argh!)

    i admit i get defensive about practically all bf’ing studies because there is already so much judgement and pressure out there about what women should do and what of course you’ll be able to do if only you believe, etc. this isn’t the fault of the studies, but it’s inevitably what happens when they hit the popular press.
    September 25, 2011 12:18 PM

    scienceofmom said…
    Someone commented somewhere recently (I can’t remember where) that what we now need breastfeeding support more than we need BF promotion. Pretty much everyone knows that they SHOULD breastfeed at this point, but they don’t always have the support to do it, which can just leave a new mama feeling overwhelmed and inadequate if things don’t go well.

    Jen – Yes, the Davis babies were probably mostly white, but they are thrown in there with babies from Brazil, Ghana, India, Norway, and Oman for the WHO dataset.
    And thanks for your thoughts on a book. I agree that what’s out there is lacking, and I think I would like to take on a project like that. I’m just not sure how to start. I am really enjoying writing for the blog and that’s working with the short amounts of time that I have right now. The blog is giving me practice and most importantly – feedback! I’m thinking about trying to write some articles for print publications or more mainstream parenting websites, but eventually I think I’d like to work on a project like a book where I can go more in depth. I do really like the Baby 411 book – that’s the main one we have used – but it doesn’t go into much detail and doesn’t explain much of the science behind their recommendations.
    September 25, 2011 2:54 PM

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    September 26, 2011
  4. Great post! Are you taking requests for future topics? 🙂 I’ve been looking for a concise comparison of the nutrition information for formula and fresh breastmilk, refrigerated breastmilk, and frozen breastmilk. I’m an exclusive pumper planning on going for 6 months (73 more days!), but I wonder if there’s a point at which stored breastmilk is inferior to formula?

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    September 26, 2011
    • Hi Catherine – This is a great question. I’ll put it on my list of questions to tackle, but I can’t promise how soon I’ll get to it. Of course it isn’t just about nutrients. Its also about immunoglobulins that help your baby resist infection – but they are probably less effective after a certain point as well. Fabulous topic – I’ll do my best to answer it!

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      September 27, 2011
      • Catherine #

        Thanks! I came across this article (http://ajph.aphapublications.org/cgi/content/short/101/8/1356) and emailed the author and she said there’s not a point where formula catches up. It sounds like there’s not enough research right now to really say, but I’d love to someday see a table showing the nutrients/contents of formula and of breastmilk at, for example, just expressed, out for x hours at room temperature, stored for x hours/days refrigerated at some temperature, and stored in a freezer at some temperature – it would be great to kind of be able to quantify the costs/benefits of giving breastmilk under different conditions.

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        September 29, 2011

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