Remember back in the old days when I used to grab whatever infant feeding study was in the news and dissect it just for the hell of it? That was fun. So much more fun than the mommy war stupidity. Statistical methods and confounding factors are way easier to understand than the intricacies of parenting-blog politics.
Let’s get back to those stress-free basics for a minute, by examining a study in this month’s issue of Pediatrics (Developmental Status of 1-Year-Old Infants Fed Breast Milk, Cow’s Milk Formula, or Soy Formula, Pediatrics, May 28, 2012) which compares the mental, motor and language status of infants fed with soy formula, infants fed with milk-based formula, and breastfed infants. Contrary to the typically sensationalist, breast-is-best portrayal the media gave of this study, it actually seemed to come from a place of real concern for infant development and feeding choice. There’s been a fair bit of scaremongering regarding soy formula in recent years; the concern is that feeding a tiny human so much soy (soy contains isoflavins, which according to the study authors, can “raise the possibility of potential estrogenic effects”) will affect that baby’s development in a negative way. It’s not clear, exactly, what these negative effects may be – man boobs? Reproductive problems? Poor neurological outcomes? Two heads? Zombie behavior? (Okay, that was probably uncouth, considering this past weekend’s bizarre news out of Miami…) Regardless, parents have been warned not to use soy formula unless their babies cannot tolerate dairy-based formula or they are vegan (which, I’m sad to report, is misleading – there is no such thing as a vegan commercial formula – there are animal-derived ingredients in every formula on the market). The authors of this study (one of whom does belong to an organization called the Soy Nutrition Institute, so there is some conflict of interest – a fact which is clearly stated at the top of the article, for the record) hypothesized that the milk-based formula-fed babies and the soy formula-fed babies would have similar development, and that the breastfed babies would score slightly higher.
Women were recruited to the Arkansas-based study during pregnancy, and all had decided prior to birth whether to feed their babies breastmilk, milk-based formula, or soy formula. The researchers followed these women and their offspring for one year, testing the babies with developmental and language assessments at 3, 6, 9 and 12 months. Their findings matched the original hypothesis – all three groups had similar scores, with the breastfed babies scoring slightly higher.
Now, the point of this study was to see if soy formula supported development as well as milk-based formula, so I’m a little confused about the inclusion of breastfed babies. I suppose one could argue that since breastfeeding is considered the biological norm, it is important to have a baseline for which to compare the different formulas… but it’s not that simple. The researchers controlled for maternal IQ and SES (socioeconomic status), as well as maternal age. However, this is just the tip of a very large and foreboding iceberg when it comes to the factors which confound infant feeding studies. There’s a table in the Pediatrics article showing the mean IQ and SES of the three groups, and these are significantly different. The mean IQ of breastfeeding mothers was 109.8; milk-based formula moms scored 106, and soy formula mamas scored the lowest at 103.8. As for SES, the moms were assigned a “score” based on highest level of education and occupation; for this category, the breastfeeding, milk-based, and soy-based mothers had scores of 49.8, 45.6, and 45.9, respectively.
These factors were controlled for, of course, meaning that the scores of the babies were “weighted” in ways which (theoretically) factored in the impact of IQ and socioeconomic status. But even within those parameters, there are important caveats: what about paternal IQ? What about childcare status: home with mom or dad, private nanny, grandparent, or daycare? What about maternal emotional state, or parenting style? What was it that made some of these women choose breastfeeding, some choose soy formula, and others choose milk-based formula?
Obviously, researchers can’t control for everything, and in the case of this particular study, in the end it didn’t really matter. The study authors explain:
In our cohort, standardized mental, psychomotor, and language development scores were very similar among the 3 feeding groups, with averages falling within the clinically normal limits….BF infants scored slightly better than formula-fed infants…These results are consistent with a large body of literature demonstrating advantages of breastfeeding on cognitive function later in life. However, it is important to point out that developmental test scores of all 3 diets groups were within the standardized norms, and differences between BF infants and formula-fed effects were quite small in magnitude and thus difficult to interpret in terms of potential clinical relevance. Previous studies have shown lesser advantages when taking into consideration confounding factors or segregating for variables such as being small for gestational age. Here, results were similar after adjusting for confounding factors and controlling for other variables of concern. Thus, our results demonstrate a potential beneficial effect of breastfeeding on cognitive function.