When Do Babies’ Digestive Systems Mature Completely?

A fetus gets its nourishment through a specialized tissue called the placenta. The baby’s digestive system takes over the process immediately after birth. The digestive system of a newborn baby is continuously developing so that it can digest human milk properly. Besides, it is also getting ready for the digestion of solids.

In this post, MomJunction tells you about the parts, attributes, and development of the baby’s digestive system from the womb to birth. It could help you make age-appropriate dietary choices.

Baby’s Digestive System: From Womb To Birth

The digestive system is responsible for breaking large food molecules into smaller ones. The broken molecules ensure adequate absorption of nutrients and the development of healthy bacteria in the gut (1).

Fetal digestive system (in the womb)

The gastrointestinal tract starts growing from the third week of gestation. By the fourth week, three distinct regions of the gut extend across the length of the embryo. These regions ultimately form different components of the gastrointestinal tract (2).

A fetal digestive system includes the mouth, esophagus, salivary glands, stomach, small intestine, large intestine, and rectum. All these digestive system parts develop in the womb itself. However, they stay functionally sterile until birth.

Newborn digestive system (full-term birth)

At full-term birth, the entire digestive system is ready to operate independently. While descending through the birth canal, the neonate system gets microbes via the vaginal microflora (3). It is a crucial occurrence as it contributes to the development of the newborn’s digestive system, including the intestinal microbial ecosystem.

This development continues as the newborn baby begins breastfeeding. For their first feed, most of the breastfed babies receive colostrum, the first milk produced after birth. Colostrum is rich in antibodies and nutrients such as fat, vitamins, and minerals that help the newborn baby grow (4). Besides, it helps in the development of the complex microorganism population that thrives in the baby’s digestive tract (5).

The changes in the baby’s body could cause a 7% loss of their birth weight within a few days (6). However, this weight loss is benign.

Newborn digestive system (preterm birth)

A premature birth leads to differences between the digestive system of a preterm and full-term baby. The development is also different, and so it the post-birth protocol. For instance, right after birth, a full-term infant is advised to breastfeed. However, this may not be the case with a preterm baby.

A premature infant may not be ready to digest human milk, particularly the proteins present in it (7). Complete digestion of milk requires digestive juices such as gastric juice and pancreatic juice along with digestive enzymes, such as amylase to digest starches and pancreatic lipase for digestion of lipids.

Most babies, both preterm and full-term, spit up frequently due to the immature digestive system or a weak and immature lower esophageal sphincter (8). However, it could also happen due to some digestive tract lining issues.

The Digestive Tract Lining Issue

An infant’s digestive tract lining is a layer of mucus that protects the digestive tract from microbes and other contaminants present in the food. At the time of birth, this lining is very thin and immature, which can increase the risk of digestive lining issues, such as inflammation and infections.

These gastrointestinal infections are dealt by antibodies present in breast milk, and it continues until the digestive mucosal lining becomes mature. While breast milk is helping the digestive tract develop its lining, it also helps in the development of gut microbiota. This is the reason why a mother’s dietary intake while breastfeeding should be healthy and planned.

In general, a baby’s digestive system continues to grow through the first two years of their life. This progression also has a direct link with the development of the baby’s immune system. Thus, the nutritional composition of the baby’s diet in the early years of life is considered crucial.

Why Should Solids Be Avoided Until Six Months?

Breastfed or formula-fed infants can usually start solids between the ages of four to six months. However, the right age may vary depending on the signs of readiness (9). Until then, solid foods are avoided because of the following reasons (10):

  • The gag reflex is underdeveloped, thus posing the risk of choking.
  • The frequency of breastfeeding would reduce, which can lead to a compromise in the intake of vital nutrients from breast milk.
  • Proper digestion of solids would be difficult as the enzymes digesting carbohydrates develop at around six to seven months of age. The bile salts and gastric lipase that help digest fat reach optimum levels between the ages of six and nine months.
  • The larger food molecules might pass through the small intestine directly into the bloodstream as infants under six months have a permeable gut. This scenario could lead to gastrointestinal tract ailments and possible allergies (11).

How To Support Your Baby’s Digestive Learning Curve?

The changes in the digestive system are rapid. Parents could take a few measures to support these developments.

  1. Exclusive breastfeeding: Several research studies have shown the breastfed infants have better digestive, respiratory, and overall health due to the complex nutritional composition of breast milk (12). Therefore, mothers should exclusively breastfeed for six months and continue breastfeeding, if possible, for up to two years.
  1. Introduction of solid foods: You can support your baby’s gastrointestinal system development by gradually introducing solids in an age-appropriate manner. As a general practice, you could do the following:
  • Introduce one food at a time with easy-to-digest foods introduced first. Soft fruits such as apple, pureed meat, poultry, beans, and iron-fortified cereals are some options to try (13).
  • As you add new food, wait for three to five days, and watch if the food is causing any discomfort to the baby. This way, you can identify a potential allergen.
  • Begin feeding solids in cooked, mashed, or pureed form. As the baby grows and develops motor skills, you may transit to soft cooked food pieces (finger foods).
  • Try to add a variety of foods to your baby’s diet right from the start so that they may reap the benefits of these foods in the long run.
  • Adjust the quantity of solid food to account for the consumption of breast milk or formula. Breast milk takes approximately an hour and a half to digest, while formula may take four to five hours.
  1. Practice hygiene: Hygiene measures while preparing baby food reduces the risk of microbial and elemental contamination.

The baby’s digestive system develops even without your intervention. However, what you can do is to support it and take care not to burden it by feeding unsuitable foods to the baby. Once the system is robust, you can experiment with foods. But until then, feed breastmilk for the first six months, and gradually introduce foods that are soft and easy to digest.


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