Is Direct From Breast Better Than Expressed Milk for Infant Weight?
Clinical Context
Despite the known benefits of breastfeeding for maternal and child health, its effect on obesity is unclear. Previous studies have shown an inconsistent association of breastfeeding with lower risk for obesity, which is a major global public health challenge and has its origins in early life; however, few of these studies documented the method of breast milk feeding, type of supplementation, or feeding in hospital.
The goals of this large, prospective CHILD birth cohort study by Holmes were to examine the association of breastfeeding, infant weight gain, and body composition in the first year of life and to determine the impact of feeding method, type and timing of complementary feeding, and formula supplementation during the neonatal period.
Study Synopsis and Perspective
Babies bottle-fed breast milk gain weight more quickly than babies nursed directly, but not as quickly as those fed exclusively or supplemented with formula long term, according to a study by Holmes published in the October 2018 issue of Pediatrics.
Previous studies have suggested that formula feeding is associated with greater weight gains among infants than breastfeeding, but little data exist regarding how specific infant feeding practices, such as formula supplementation for breastfeeding babies or feeding expressed breast milk via bottle, affects weight gain. The new study by Holmes shows that how babies are fed breast milk matters.
"Breastfeeding is inversely associated with weight gain velocity and BMI [body mass index]," wrote Meghan Azad, PhD, assistant professor of pediatrics and child health at the University of Manitoba in Winnipeg, Manitoba, Canada, and coauthors. "These associations are dose dependent, partially diminished when breast milk is fed from a bottle, and substantially weakened by formula supplementation after the neonatal period."
The new study followed 2553 mother-infant pairs in Canada between 2009 and 2012 to document how breastfeeding and other feeding practices affected the child's weight gain and BMI at 1 year of age.
Exclusive breastfeeding at 3 months was associated with slower weight gain and lower BMI at 1 year than all other feeding regimens. Brief formula supplementation after birth or adding solid foods before 6 months didn't reduce these benefits; however, later formula supplementation was associated with faster weight gain and higher BMI, adding 0.28 to the average BMI z score, and exclusive formula feeding later led to even greater gains (0.45 BMI z score).
Infants who consumed some breast milk from a bottle also saw a small increase in weight gain (0.12 BMI z score).
The study population was unusual in that 97% of the women enrolled in the CHILD study initiated breastfeeding. They averaged 4 months of exclusive breastfeeding and reported a median of 11 months of any nursing.
In an accompanying editorial, Alison Volpe Holmes, MD, MPH, associate professor of pediatrics at the Dartmouth Geisel School of Medicine in Lebanon, New Hampshire, noted this likely reflects Canada's generous maternity leave policies, which guarantee a minimum of 15 months of paid leave and preserve women's jobs for 17 to 52 weeks of leave. By contrast, the United States guarantees no paid leave and offers only 12 weeks of job protection to a subset of individuals under the Family and Medical Leave Act.
Despite the unusually high rate of breastfeeding in the cohort, the study offers unique insights on how different feeding practices might affect infant weight gain. Dr Holmes noted that the study is one of the first to look at specific feeding practices, such as feeding only at the breast or feeding breast milk with bottles.
The study provides reassurance for those parents introducing solid foods before 6 months in an effort to reduce the risk for food allergies, Holmes wrote. It also showed that brief formula feeding in the hospital after birth didn't alter weight if mothers switched to exclusive breastfeeding.
"Our study also found that the method of feeding breastmilk matters," study author Dr Azad said in a press release. "Feeding expressed breastmilk from a bottle appeared to have a weaker beneficial effect on infant weight compared with direct feeding at the breast, although expressed milk was still beneficial compared to infant formula."
Dr Holmes suggested that direct feeding at the breast may lead to less weight gain than bottle-feeding breast milk because it is "infant-led." It's also possible that breast milk loses some protective factors during storage, Dr Holmes noted.
Children in the CHILD study cohort will be followed through adolescence so study investigators will be able to follow whether infant feeding practices have longer-term effects on weight.
"With this report, and more to come, pediatricians have new and better evidence to advocate for family leave and workplace support policies that protect breastfeeding mothers and infants, and improve public health," Dr Holmes wrote.
Dr Azad disclosed receiving travel expenses from Mead Johnson & Company, LLC for a presentation about breast milk and from Medela LLC for attending a breast milk conferences. Her coauthors and Dr Holmes have disclosed no relevant financial relationships.
Study Highlights
In the CHILD birth cohort study, 2553 mothers reported their feeding practices, which were confirmed from hospital records.
At 12 months of age, children were measured for weight and BMI z scores.
Most (97%) mothers initiated breastfeeding (median duration, 11.0 months; average duration of exclusive breastfeeding, 4 months).
Before 6 months of age, 74% of infants had received solid foods.
Among infants described by their mothers as "exclusively breastfed," 55% received some expressed breast milk and 27% briefly received formula while in the hospital.
At 3 months of age, infants who received exclusive direct breastfeeding had lower BMI z scores than infants subjected to all other feeding styles.
Adjusted β was +0.12 for some expressed milk (95% CI: 0.01, 0.23), +0.28 for partial breastfeeding (0.16, 0.39), and +0.45 for exclusive formula feeding (0.30, 0.59).
In the first year of life, breastfeeding was inversely associated with weight gain velocity, BMI, and overweight risk, in a dose-dependent fashion, as longer and more exclusive breastfeeding strengthened the associations.
Analyses controlled for maternal BMI, socioeconomic status, and other potential confounders did not affect the observed associations.
Compared with exclusive breastfeeding, stopping breastfeeding before 6 months was associated with 2-fold increased risk for rapid weight gain, +0.44 standard deviation (SD) increase in BMI by 12 months old, and 3-fold increased risk for overweight.
These effects considerably exceed the estimated effect of maternal obesity (+0.20 in the same multivariable model).
As long as exclusive breastfeeding was established and sustained for at least 3 months, brief formula supplementation in hospital did not markedly affect these associations.
Formula supplementation by 6 months was associated with higher BMI zscores (adjusted β, +0.25 [95% CI: 0.13, 0.38]), but supplementation with solid foods was not.
According to their findings, the investigators concluded that breastfeeding is inversely associated with weight gain velocity, BMI, and overweight risk during infancy, in a dose-dependent fashion.
Feeding breast milk from a bottle partially reduced these associations, and supplementation with formula, but not with solid food, after the neonatal period markedly weakened these associations.
The study offers new evidence to inform feeding recommendations and future research regarding how infant feeding practices affect the development and prevention of childhood obesity.
This study and previous evidence suggest that direct breastfeeding offers the strongest protection against rapid weight gain and overweight whereas bottled breast milk offers intermediate protection.
This has important policy implications because the leading reason for feeding bottled breast milk is return to work, which is strongly affected by national and institutional maternity leave policies.
Although a single formula feeding in the hospital did not significantly affect the benefits of otherwise exclusive breastfeeding, supplementation may discourage or delay breastfeeding initiation and decrease a new mother’s confidence in her ability to breastfeed, which may result in early cessation or continued supplementation.
Future studies should address possible effects of brief supplementation on other factors such as inflammation, immunity, or the gut microbiome.
Potential mechanisms underlying the associations between feeding practices and infant weight may also include biological differences in the macronutrient profiles of formula vs breast milk and presence in human milk but not in formula of bioactive components that may be altered or degraded during milk expression and storage.
These bioactive components include hormones regulating satiety, microbiota seeding the infant gut, and oligosaccharides supporting microbiota development.
In additional, the "baby-led" nature of breastfeeding may encourage satiety responsiveness later in childhood.
Study limitations include the lack of quantitative information about the amount of expressed milk or formula consumed; limited power to determine the effect of never breastfeeding; lack of data regarding mothers’ intentions to breastfeed, feeding styles, or reasons for supplementing, pumping, and weaning; and observational design with possible residual confounding.
In addition, the findings may not be generalizable to other settings with different breastfeeding practices and policies or to populations challenged with undernutrition and stunting rather than overnutrition and obesity.
An accompanying editorial noted that the very high rate (97%) of breastfeeding may reflect liberal maternity leave policies in Canada and that the findings create no concern regarding solid food introduction before 6 months to lower the risk for food allergies.
Possible reasons for less weight gain with nursing than with bottle-feeding breast milk may be that direct feeding at the breast is initiated and regulated by the infant and that breast milk may lose some protective factors during storage.
Findings from this study and from an ongoing follow-up of CHILD study cohort participants through adolescence provide pediatricians with new, better evidence to advocate for family leave and workplace support policies that facilitate breastfeeding and thereby improve public health.
Clinical Implications
Breastfeeding is inversely associated with weight gain velocity, BMI, and overweight risk during infancy, in a dose-dependent fashion, and feeding breast milk from a bottle partially reduced these associations.
This large, prospective CHILD birth cohort study and previous evidence suggest that direct breastfeeding offers the strongest protection against rapid weight gain and overweight whereas bottled breast milk offers intermediate protection.
Implications for the Healthcare Team: This has important policy implications because the leading reason for feeding bottled breast milk is return to work, which is strongly affected by national and institutional maternity leave policies.