The Influence of Maternal BMI and Breastfeeding on Infant BMI
by Anne Eglash MD, IBCLC, FABM
What is the relationship between maternal pre-pregnancy BMI, breastfeeding, and infant BMI?
Numerous studies have shown that breastfeeding decreases an infant’s risk of developing childhood obesity. However, some critics argue that this relationship may actually reflect genetic factors, rather than a direct effect of breastfeeding itself. Their reasoning is that parents with higher BMIs are less likely to start and continue breastfeeding their babies. Therefore, the apparent protective benefit of breastfeeding could simply be because infants born to healthier-weight parents are both more likely to be breastfed and less likely to become obese due to genetic reasons.
The majority of past studies examining the protective effects of breastfeeding against childhood obesity have had inadequate sample sizes to determine whether the mother’s BMI influences this relationship.
The authors of today’s study aimed to identify associations between breastfeeding and child BMI according to maternal pre-pregnancy BMI by analyzing data from the US Environmental Influences on Child Health Outcomes (ECHO) Program.
The ECHO program includes 69 diverse pediatric cohorts around the USA designed to evaluate early life exposures on pre-, peri, and postnatal outcomes, upper and lower airway disease, obesity, neurodevelopment, and positive health.
The researchers analyzed data from 8,134 dyads, including pre-pregnancy maternal BMI, infant feeding practices, and child BMI measured between ages 2 and 6.
Several covariates were included such as the child’s sex, maternal education, maternal age, use of nicotine products, and maternal race/ethnicity.
Before pregnancy, 2.5% of the mothers were underweight, 45.8% were a healthy weight, 26% were overweight, and 25.6% were obese. Approximately 17% of the mothers identified as Black, 58% white, and the rest either Asian, Hispanic, or multi-racial.
After adjusting for the above covariates, the authors found that breastfeeding, whether exclusive or not, for 6 months was associated with lower BMI among children whose mothers had a pre-pregnancy weight that was either healthy, overweight or obese.
- Infants of mothers in the underweight category breastfed longer than mothers in the healthy weight category.
- Infants of mothers with a pre-pregnancy BMI in the obese category were breastfed for the shortest duration.
- By 6 years of age, there was no difference in childhood BMI according to breastfeeding duration or intensity.
- Each additional month of breastfeeding, exclusive or not, was associated with a lower child BMI among mothers who were obese.
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Abstract
Objectives
Breastfeeding practices may protect against offspring obesity, but this relationship is understudied among women with obesity. We describe the associations between breastfeeding practices and child BMI for age z-score (BMIz), stratified by maternal BMI.
Methods
We analyzed 8134 dyads from 21 cohorts in the Environmental Influences on Child Health Outcomes Program. Dyads with data for maternal pre-pregnancy BMI, infant feeding practices, and ≥1 child BMI assessment between the ages of 2 and 6 years were included. The associations between breastfeeding practices and continuous child BMIz were assessed by using multivariable linear mixed models.
Results
Maternal pre-pregnancy BMI category prevalence was underweight: 2.5%, healthy weight: 45.8%, overweight: 26.0%, and obese: 25.6%. Median child ages at the cessation of any breastfeeding and exclusive breastfeeding across the 4 BMI categories were 19, 26, 24, and 17 weeks and 12, 20, 17, and 12 weeks, respectively. Results were in the hypothesized directions for BMI categories. Three months of any breastfeeding was associated with a lower BMIz among children whose mothers were a healthy weight (0.02 [0.04 to 0.001], P 5.06), overweight (0.04 [0.07 to 0.004], P5.03), or obese (0.04 [0.07 to 0.006], P5.02). Three months of exclusive breastfeeding was associated with a lower BMIz among children whose mothers were a healthy weight (0.06 [0.10 to 0.02], P5.002), overweight (0.05 [0.10 to 0.005], P5.07), or obese (0.08 [0.12 to 0.03], P5.001).
Conclusions
Human milk exposure, regardless of maternal BMI category, was associated with a lower child BMIz in the Environmental Influences on Child Health Outcomes cohorts, supporting breastfeeding recommendations as a potential strategy for decreasing the risk of offspring obesity.
This study stands out for its uniquely large cohort, which enabled the researchers to thoroughly evaluate the relationship between three key factors: maternal BMI prior to pregnancy, duration of breastfeeding, and the child’s BMI later in life. Importantly, they were also able to account for other variables known to reduce how long overweight and obese mothers breastfeed.
Infants born to underweight mothers were breastfed for a shorter duration than infants of mothers with a healthy pre-pregnancy body mass index.
Even for children at 6 years of age, the study found lower BMI to be associated with increased breastfeeding duration among children of overweight and obese mothers. In particular, the authors calculated that 6 months of exclusive breastfeeding would lead to a reduction in average childhood BMI by 0.15 standard deviations for children of obese women. The authors point out that 4 million American women of childbearing age are obese, such that this potential decrease in BMI would impact millions of children in the United States alone.
The results of this study are supported by a World Health Organization European child obesity surveillance study from 22 countries, which also found that breastfeeding for 6 months protected from child obesity.
Allison
It would be interesting to see if anyone followed up to why overweight or obese women stopped breastfeeding earlier than their “healthy” weight peers.
Both insulin resistance and thyroid conditions can lead to obesity and both can complicate breastfeeding, and both are often undiagnosed.
This may just be one more example of how fat shaming extends well beyond one’s actual weight.
IABLE
There is a wealth of research on reasons why people who are overweight or obese stop breastfeeding earlier than their peers with a ‘healthy’ BMI, such as decreased self efficacy and low milk production. Low milk production, as you point out, can be due to underlying insulin resistance that occurs for some people with elevated BMI.
Allison Harrison
That’s what I was getting out.
Rather than framing the original concept that people that are overweight don’t breastfeed as long, we serve our patients best to realize obesity may be a side effect of something else, which also can impact breastfeeding. That is the correlation that those outside of the lactation field are seeming to miss, such as primary care providers and OBGYNs