Breastfeeding and Obesity

Introduction

It is no secret that obesity is on the rise in both children and adults. The estimated percentage of US children aged 2–5 years and 6–11 years classified as overweight increased from 5% and 6.5% in 1980 to 10.4% and 19.6% respectively in 2007–2008. ¹ Obesity rates in the 6–23-month age group rose from 7.2% in 1980 to 11.6% in 2000. These statistics are concerning given the long-term health consequences associated with obesity. There is emerging evidence that points to breast milk and lactation as interventions that can reduce obesity and improve health. Breast milk and lactation are modifiable lifestyle behaviors that decrease the likelihood of developing obesity and its sequelae in both mother and child.

Infants who receive a diet of breast milk reap the benefits of good nutrition during infancy and long after the breastfeeding period. A 2007 systematic review of the effects of breastfeeding on maternal and infant health demonstrated increased incidences of acute otitis media, gastroenteritis, atopic dermatitis, and life-threatening conditions including severe lower respiratory infections, necrotizing enterocolitis, and sudden infant death syndrome in infants receiving formula derived from cow's milk. ²

Effect of Lactation on Childhood Obesity

Early life nutrition and weight gain velocity during the first months of life influence childhood growth and fat patterning. Reports have demonstrated that feeding practices in the first year of life affect growth and body composition and that breast-fed infants gain weight less rapidly than formula-fed infants. ¹ The World Health Organization (WHO) and the Centers for Disease Control (CDC) recommend the use of the 2006 WHO growth charts (Table 1) to assess growth in infants accurately. The 2006 growth charts demonstrate normal growth patterns of breast-fed babies. In general, the baby receiving breast milk has more rapid growth in the first few months of life than formula-fed babies. At 3–12 months of age, breast-fed babies have a decreased growth velocity versus formula-fed infants. In the past, breast-fed infants may have been supplemented during this period of slow growth to maintain weights comparable to formula-fed infants. The WHO suggests the revised growth charts are prescriptive in nature and more accurately predict the child at risk for obesity. ³

Several studies link long-term obesity reduction with breastfeeding in infancy. In a report from Bavaria, Germany, children who were breast-fed had nearly one-half the rate of obesity than those children who were formula-fed (2.8% vs. 4.5%). ⁴ Infants who breast-fed longer than 12 months had the lowest rate of obesity (0.8%). The duration of breastfeeding is inversely related to pediatric overweight. For each month of breastfeeding up to the age of 9 months, the odds of overweight decreased by 4%. ⁵ This decline resulted in more than a 30% decrease in the odds of overweight for a child breast-fed for 9 months when compared to a child who never breast-fed. ⁵

The exact mechanisms for which breastfeeding reduces the risk of obesity is unknown. It is theorized that breastfeeding might have a programming effect in preventing obesity or becoming overweight later in life. Significantly higher plasma concentrations of insulin have been found in infants who were bottle-fed than in infants who were breast-fed. ⁶ These higher concentrations of insulin would be expected to stimulate fat deposition and the early development of adipocytes. Epidermal growth factor and tumor necrosis factor, two bioactive factors found in breast milk, are known to inhibit adipocyte differentiation in vitro. ⁷

Another theory suggests that breastfeeding, as opposed to bottle feeding, promotes a less restrictive feeding style that is more responsive to the infant's hunger cues and satiety, thus allowing the infant greater self-regulation of energy intake, preventing overfeeding and excessive weight gain. ⁸ Li et al. found that infants categorized as “breast-fed and human milk by bottle” grew similarly to those fed only at the breast, but infants categorized as “breast-fed and formula by bottle” grew more rapidly. This would suggest that supplementing breastfeeding with expressed breast milk is preferable to supplementing breastfeeding with formula when strictly feeding at the breast is not feasible. ⁹

The amount of energy metabolized and the protein intake of breast-fed infants is significantly less than the intake of those infants who are fed formula. Longitudinal studies found a significant relationship between dietary protein intake at 10 months of age and later body mass index and body fat distribution. ⁷ These studies suggest that a high intake of protein in early childhood may increase the risk of obesity later in life. Animal studies demonstrate the availability of protein during fetal and postnatal development have long-term effects on metabolic programming of glucose metabolism and body composition in adult life. ⁷ Promoting prolonged breastfeeding may help to decrease the prevalence of obesity in childhood. Since it is known that obese children have a high risk of becoming obese adults, such preventive measures should result in a reduction in the prevalence of cardiovascular disease and other diseases that are known to be associated with obesity.

Effect of Lactation on Maternal Obesity and Metabolic Disease

Recently a large number of studies have demonstrated the impact of lactation on obesity and its associated sequelae for women throughout out the lifespan. Table 2 summarizes the benefits of lactation to both infants and mothers. It is widely recognized that breastfeeding enhances maternal weight loss in the immediate postpartum period. ¹⁰ It is estimated that lactation requires an additional intake of 480 kcal per day by the mother to produce adequate milk supply. In addition, the process of lactation improves lipid and glucose metabolism. C-reactive protein (CRP) levels, a marker for inflammation, are also reduced during lactation. ¹⁰ Elevated CRP levels are associated with an increased risk of myocardial infarction, sudden death and stroke. ¹¹

A 2009 study of 139,681 post-menopausal women who reported at least one live birth demonstrated a marked correlation between numbers of months of lactation in a lifetime and decreased cardiovascular risk factors such as hypertension, diabetes, and hyperlipidemia. In fact, women who had breast-fed for more than 12 months in their lifetime were less likely to develop cardiac disease. Cardiac risk factors are frequently associated with obesity. In this study, there was a small reduction in basal metabolic index (BMI) rates in the women who had breast-fed versus bottle feed for greater than 12 months. However, women with a lactation history reaped the benefit of reduced cardiac risk factors regardless of BMI. ¹²

Ram et al. (2008) studied 2,516 women and compared duration of lactation with the likelihood of development of metabolic syndrome in midlife. ¹³ Metabolic syndrome, which is comprised of insulin resistance, dyslipidemia, hypertension, and obesity, was reduced in women with a history of lactation. Duration of lactation was closely correlated with decreased incidence of metabolic syndrome in midlife. In addition, abdominal obesity was reduced in women with a lactation history. These findings were even noted in women with a lactation history and an unhealthy lifestyle, including smoking and poor diet. Despite unhealthy life choices, women with a lactation history had a decreased risk of development of metabolic syndrome. It appears that lactation is protective and dose related. Longer duration of lactation is associated with decreased risk of metabolic syndrome. ¹³

A 2005 systematic review of the literature that evaluated the association of lactation with gestational diabetes (GDM) reported improved glucose tolerance levels of Latina women with gestational diabetes who breast-feed during the postpartum period. Latina women with a history of gestational diabetes who did not breast-feed were at a twofold higher risk of developing postpartum diabetes. ¹⁴ These findings are supported in a 2012 prospective study of 83,585 women. Stuebe et al. (2012) reported that parous women who had a lactation history were less likely to develop type 2 diabetes. Longer duration of lactation was associated with decreased incidence of diabetes. The authors propose that lactation may improve glucose homeostasis. ¹⁵

Several studies report that women with diabetes are less likely to breast-feed their infants than women without diabetes. This may be related to high complication rates in diabetic mothers and their infants in the newborn period. ¹⁴ Stuebe et al. (2005) cite several studies that suggest that obesity and insulin resistance at time of delivery negatively impacts breastfeeding outcomes. ¹⁵

Impact of Obesity on Breastfeeding

Overweight and obese women breast-feed for shorter periods of time versus normal-weight women. It is noted that women with a BMI>27 are 2.5 times more likely than normal-weight women to have a delayed onset of lactation. Overweight and obese women are also noted to have a delayed prolactin response to nursing at 48 hours postpartum. ¹⁶ The prolactin response to the infant suck is critical in the early postpartum period for milk production. ¹⁷ This may explain some of the lower breastfeeding rates in overweight and obese women.

Amir and Donath conducted a systematic review of the literature related to maternal obesity and breastfeeding. This review supports previous studies demonstrating decreased breastfeeding rates in obese women. The authors noted that three studies reported a relationship between obesity and delayed lactogenesis. The physiologic cause for the delay in lactogenesis is not clear. The authors also suggest poor breastfeeding rates may be multi-factorial and related to biology, psychology, and culture. ¹⁸

A 2006 prospective study of 1,803 children and their mothers noted that overweight and obese women were less likely to initiate and maintain breastfeeding beyond the first few weeks postpartum as compared to their normal-weight counterparts. ¹⁹ This is unfortunate, since the benefits of lactation for mother and baby are related to length of time of breastfeeding. The authors report this lack of successful breastfeeding in obese women may be related to altered hormone levels, high energy demands of larger-sized infants, or difficulty for the infant in latching onto a larger breast. ¹⁹

Conclusion

Breastfeeding has many positive outcomes for both child and mother. The duration of lactation is associated with improved maternal glucose and insulin levels and reduced cardiovascular risk factors. While the long-term effect of lactation on weight gain is inconclusive, there is evidence to support the benefit of lactation on immediate postpartum weight loss. Current literature supports the view that obese women will benefit from breastfeeding, since they are already at an increased risk of cardiac disease. The challenge exists in that these are the very same women who are least likely to breast-feed. It is reasonable to propose that breastfeeding improves women's health. It is prudent to suggest that since obese women are at increased risk of metabolic syndrome, they would benefit from strong lactation support and education in the prenatal and postpartum period.

Breast milk has traditionally been recognized as the preferred nutrition for infants due to its association with improved infant outcomes and decreased infection rates. Recent reports have focused on the benefits of breastfeeding and breast milk for both mother and baby to reduce the risk of obesity and associated cardiac risk factors. Breast milk and lactation are potential modifiable risk factors related to cardiac disease later in life and can be recommended to reduce the risk of cardiac disease. Incorporation of breastfeeding education and the benefits of lactation should be woven into anticipatory guidance discussions with women of childbearing age.