Baby feeding with eyes closed.

Your baby’s growing digestive system

From digestive tract development to the key role breastfeeding plays in strengthening the immune system, your baby’s digestive system could determine her overall health.

The digestive system starts to grow from day one, but it still needs help

Nourished and protected by your placenta in the womb, your baby’s digestive system and excretory system start to work on their own as soon as she is born. However, her gastrointestinal (GI) tract is still developing and will need essential fats, proteins, carbohydrates, hormones, vitamins, and minerals in order to grow for the first six months to a year.

Quick stomach growth, one tiny feeding at a time

Your baby’s stomach is roughly as large as a small marble at birth and, after a few days, will grow to about the size of a ping-pong ball — a capacity between 1.5 ounces and 2 ounces. Until she’s about 4 months old, your baby’s stomach can hold only small amounts of milk at a time. This is one of the main reasons why you have to feed her so often early on — up to 10 times per day at first.

Because her esophagus is still developing (in fact, the opening at her stomach does not close completely yet), she might spit up during or after feedings. It is not painful, and she might not even realize she has done it. If your baby is healthy and gaining weight, it is just part of the development process; however, if your baby spits up more than a tablespoon at a time (or if the spit-up is associated with respiratory symptoms such as choking, coughing, or wheezing), ask your health care professional if there is a reason to be concerned. Learn more about how to tell if it’s spit-up or vomit, and what you can do about it.

Your baby’s immune system will need to be nourished

Your baby’s immune system does not fully develop until she is 4 or 5 years old. Breastfeeding your baby as long as possible, especially during the first 12 months, can help prevent infections and illness as the immune system matures. This can be aided even further by choosing the proper nutrition while you are breastfeeding to help provide the antibodies and beneficial bacteria your baby’s immune system needs to protect against viral infections, fungi, and parasites — most notably during the first six months. This added protection, in addition to vaccinations, allows her immune system to “catch up” and begin producing its own antibodies.

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