The rate of cesarean-section births in many countries is over 15 percent, and in some settings, cesarean delivery has become more common than vaginal delivery. Cesarean-section birth is medically necessary in many cases, but not in all cases. A recent meta-analysis published in the International Journal of Obesity found that cesarean section is associated with a 33 percent increased risk of later developing obesity or weight gain.1

When an infant passes through the birth canal, she ingests the mother’s vaginal bacteria, which is filled with beneficial bacteria that colonize the infant’s gut. “In cesarean-born newborns, the lack of or delay of early-life exposure to maternal vaginal and intestinal bacteria could alter the normal development of their immune system and thus increase susceptibility to atopic, allergic, and autoimmune disease,” stated the researchers. “Compared with those born vaginally, newborns delivered by cesarean section had fewer intestinal Bifidobacteria and Bacteroides, both of which were reported to be protective factors against later obesity.”

The researchers found that both males and females were at similar risk, and that this risk might persist from childhood to adulthood. “It is worthy to note that even a modest risk would have significant public health implications, given the high relevance of both cesarean section and obesity in many countries,” they stated.

This study is important because it analyzed nine studies on the topic, including one that I blogged about last year. They call for more studies investigating the underlying mechanism of the association, citing the hygiene hypothesis as the likely reason for the increased risk. According to the hygiene hypothesis, in the ultra-clean modern world, infants are not exposed to enough commensal microbes that would help to educate their immune systems for optimal immune development.

The establishment of gut bacterial balance during infancy—and maintenance of this diversity throughout life—plays a fundamental role in our health. Doing everything we can to restore intestinal balance is a crucial part of getting and staying healthy.



  1. Li HT, Zhou YB, and Liu JM, “The impact of cesarean section on offspring overweight and obesity: a systematic review and meta-analysis.” Int J Obes (Lond). 2013 Jul;37(7):893-9.