Bottle Feeding, Breastfeeding, and BMI
by Anne Eglash MD, IBCLC, FABM
Obesity is increasing in nearly every country in our world. Because childhood obesity increases the risk of adult obesity, finding strategies to prevent childhood obesity may help to reduce the rising tide of adult obesity. Many studies, but not all, have shown that breastfeeding is associated with less obesity. The question is whether feeding directly from the breast has a lower rate of obesity as compared to bottle feeding expressed breast milk. In addition, is there a difference in risk of obesity between bottle feeding expressed breastmilk and formula feeding?
Several researchers evaluated the feeding practices of 2553 mother-infant dyads who were in the Canadian CHILD birth cohort. They evaluated the BMI of infants who were exclusively fed via the breast for 6 months, those who partially or fully bottle-fed expressed breastmilk, and those who were formula fed. They also evaluated the effect of timing of complementary feedings on BMI.
- For exclusively breastfed infants, adding solids before 6 months (at 5 months) increased their BMIs.
- Among infants who were exclusively breastfed for at least 3 months, those who received formula supplementation in the first month tended towards a higher BMI.
- Infants who were not breastfeeding at 6 months had a 3x increased risk of overweight compared to infants who were exclusively breastfeeding at 6 mo.
- Breastfed infant who received some breastmilk in a bottle had a faster rate of weight gain as compared to infants who were exclusively fed at the breast.
- Bottle feeding breastmilk leads to the same risk of overweight as bottle feeding formula.
See the Answer
Studies addressing breastfeeding and obesity rarely document the method of breast milk feeding, type of supplementation, or feeding in hospital. We investigated these practices in the CHILD birth cohort.
Feeding was reported by mothers and documented from hospital records. Weight and BMI z scores were measured at 12 months. Analyses controlled for maternal BMI and other confounders.
Among 2553 mother-infant dyads, 97% initiated breastfeeding, and the median breastfeeding duration was 11.0 months. Most infants (74%) received solids before 6 months. Among “exclusively breastfed” infants, 55% received some expressed breast milk, and 27% briefly received formula in hospital. Compared with exclusive direct breastfeeding at 3 months, all other feeding styles were associated with higher BMI z scores: adjusted β: +.12 (95% confidence interval [CI]: .01 to .23) for some expressed milk, +.28 (95% CI: .16 to .39) for partial breastfeeding, and +.45 (95% CI: .30 to .59) for exclusive formula feeding. Brief formula supplementation in hospital did not alter these associations so long as exclusive breastfeeding was established and sustained for at least 3 months. Formula supplementation by 6 months was associated with higher BMI z scores (adjusted β: +.25; 95% CI: .13 to .38), whereas supplementation with solid foods was not. Results were similar for weight gain velocity.
Breastfeeding is inversely associated with weight gain velocity and BMI. 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.
This is a large study that did a nice job separating out the effects of direct breastfeeding, bottle feeding breastmilk, and bottle feeding formula on BMI. It also evaluated the effect of early solids introduction on BMI.
The results in this study found that adding solids at 5 months of age did not increase the BMI as is typically found by adding in formula under 6 months. Infants who exclusively breastfed for 6 months did not demonstrate a rise in BMI as a result of some formula supplementation in the first few weeks of life. Bottle feeding breastmilk did increase the BMI as compared to direct breastfeeding, but bottle feeding breastmilk had less effect on the BMI than bottle feeding formula.
The study took into account several confounding factors that influence BMI such as maternal age, ethnicity, education, marital status, maternal smoking status, maternal pre-pregnancy BMI, and infant birth weight.
The authors mention in their discussion that we need more research to understand the results. The differences in BMI between bottle feeding formula vs bottle feeding breastmilk, vs direct breastfeeding could be related to lack of factors in formula that regulate appetite, changes in gut microbiota in formula fed infants, bottle feeding technique (such as paced vs non-paced feeding), and/or the effect of breastmilk storage on the bioactive factors in breastmilk.
This is not the first study to show that bottle feeding breastmilk leads to a higher BMI as compared to direct feeding. This is a potential risk to share with families who ask whether pumping and bottle feeding leads to the same health outcomes as direct breastfeeding.