In a recently released article in Pediatrics, Dr. Meghan Azad and a team of researchers from Canada and abroad share their landmark work on infant feeding and risk of rapid weight gain through age 12 months (10.1542/peds.2018-1092). This well conducted prospective study examines the separate effects of duration, exclusivity and type of breast milk feeding (at breast versus expressed), and of formula supplementation and complementary feeding, on infant growth as measured by BMI-for-age z score and weight-for-age z score at 12 months. BMI (body mass index) is well known to pediatricians as weight divided by length or height squared; a z score is simply a standard deviation. The authors defined overweight as a BMI-z score > 2, and defined rapid weight gain velocity as a change in weight-for-age z score from birth to 12 months of >0.67. Great strengths of the study include the large number of participants (2,553), the high number of relevant covariates including maternal BMI, and the broad range of participant feeding patterns with a substantive proportion of breastfed infants. Dr. Alison Holmes’ thoughtful commentary gives an excellent overview and zooms in on what are (to me also) the most interesting aspects of the study: the impact of expressed breast milk versus breast milk from the breast (nursing) on weight gain patterns, and associated societal issues relating to support of exclusive breastfeeding.
Dr. Azad and colleagues’ work has multiple implications. For example, their study data permits parsing out of the independent contributions of formula supplementation versus complementary feeding on 12 month obesity outcomes, and this is golden information for readers. An analysis of infants who received formula briefly in-hospital, and then went on to exclusively breastfeed for 3 months or more, is highly reassuring in its lack of identified impact on obesity outcomes. More nuggets await you as you read this fascinating paper. Their work provides a ringing endorsement for exclusive breastfeeding through 6 months of age with continued breastfeeding and complementary foods beyond that age, as recommended by the AAP. The authors are careful not to over-reach, and caution that their results apply to first year of life obesity outcomes only.
Dr. Azad and colleagues found that both exclusivity and duration are independently associated with being leaner at 12 months. However, as foreshadowed in earlier work1, infants who received breast milk from a bottle had lower BMI-z scores at 12 months than those who received formula, but had higher BMI-z scores than those receiving breast milk only at the breast. I believe that the implications of this key finding are that mothers need financial, logistical and personal support well beyond what is currently available to have a chance to set and reach optimal goals for their own breastfeeding. As Dr. Holmes emphasizes (10.1542/peds.2018-2297), the U.S. has a highly regressive maternity leave policy: it is the only industrialized country, and one of just 4 countries worldwide (Swaziland, Lesotho, Papua New Guinea, U.S.) that lacks paid maternity leave. Women working outside of the home at all ends of the work spectrum from law firms to fast food chains face discrimination and lack of employer knowledge and willingness to comply with the law about milk expression in the work place.2 We also know that working outside the home full time decreases breastfeeding initiation, exclusivity and duration,3,4 so this is a societal issue that we cannot continue to ignore. This important work by Azad and colleagues is critical evidence to bring to the bargaining table.
References
1. Li R, Magadia J, Fein SB, Grummer-Strawn LM. Risk of bottle-feeding for rapid weight gain during the first year of life. Arch Pediatr Adolesc Med. 2012 May;166(5):431-6.
2. United States Department of Labor, Wage and Hour Division. Frequently Asked Questions – Break Time for Nursing Mothers. https://www.dol.gov/whd/nursingmothers/faqBTNM.htm [accessed 9/2/2018].
3. Andres E, Baird S, Bingenheimer JB, Markus AR. Maternity Leave Access and Health: A Systematic Narrative Review and Conceptual Framework Development. Matern Child Health J. 2016 Jun;20(6):1178-92.
4. Bai DL, Fong DY, Tarrant M.Factors associated with breastfeeding duration and exclusivity in mothers returning to paid employment postpartum. Matern Child Health J. 2015;19(5):990-9.
