UNC Health Care
graphic of baby being spoon-fed

How a Baby’s Digestive System Works, for Parents

What should a baby eat? How much and how often? When can you give a baby solids?

These are just some of the questions a parent thinks about when caring for an infant. It’s very important that babies receive adequate nutrition to grow and develop, but it can be hard to know how to feed them. It helps to understand what’s going on inside their digestive systems.

The Baby Diet

Within the first few hours of life, a newborn will have his or her first meal.

“Breast milk or formula are the only two options for a baby to consume during the early months of life because a baby can’t chew and swallow solid food yet,” says Ricardo Baler, MD, UNC Health pediatrician.

If a mother is breastfeeding, she’ll notice small amounts of a protein-rich substance called colostrum coming out of the breasts first for the baby to eat. Formula-fed babies will consume about a half-ounce of formula during those early hours. From that point on, every two or three hours a newborn will consume about 2 ounces of milk, whether from breast or bottle (though you can’t measure what’s coming from the breast). As the baby continues to grow, the stomach begins to expand.

“The capacity for a baby’s stomach right at birth is about half an ounce to 1 ounce. By the end of the first week, a lot of babies are eating twice that. It’s a rapid stretch to hold more,” says Edward Pickens, MD, UNC Health pediatrician.

When it comes to feeding a baby, it’s all about following cues. Watch out for hints of hunger; hungry babies might suck on their lips or tongue, put their fingers in their mouth or cry.

The best way to confirm that a baby is eating enough is to monitor weight gain. Growth spurts typically happen when a baby is 2 to 3 weeks, 6 weeks, 3 months and 6 months old.

Starting between 4 and 6 months of age, a baby is typically ready for solids. A baby who is ready has good head and neck control, can sit with little or no support and might open his or her mouth and lean forward when food is near.

It’s important for a baby to eat a variety of foods such as fruits, vegetables, grains, yogurt, cheese and meat. Foods that can be made into a pureed form are best when introducing solids. Pediatricians recommend that parents introduce one food at a time to the baby, then wait a couple of days to try something different. This will allow time to see if the baby has any allergic reactions.

“Give the baby time to explore the food in front of them. It’s great for the baby to touch the food and experience its taste,” Dr. Baler says.

At mealtime, feed solid food first and then finish with milk. Around the first birthday, food becomes the primary source of calories and milk becomes secondary.

What to Know About Baby Poop

The first bowel movement after a baby is born is meconium. This green-black, sticky lining of the intestines flakes off and collects before birth.

“It takes about 24 hours once the meconium is gone for milk to complete its course through the digestive system to eventually lead to a bowel movement,” Dr. Pickens says.

There’s a huge range of normal when looking at an infant’s stool color. Green, brown or yellow “seedy” poop is common to see in a diaper in the early months of life. Oftentimes, the poop can be runny or of a liquid consistency, which is not a cause for concern.

When a baby is born, his or her digestive system is fairly inefficient. As the baby learns to pass stool he may strain, grunt, cry or turn red in the face. As long as the stool is soft, this is not due to constipation.

A baby might experience gas while digesting milk or after swallowing air while crying. Changing the baby’s position or “bicycling” his or her legs might help, and some parents swear by an over-the-counter supplement called gripe water.

But oftentimes, there’s nothing that can be done about gas, and it’s normal and OK, Dr. Pickens says.

“There’s a certain amount of gassiness and a certain amount of fussiness that cannot easily be fixed, but it gets better in time. Newborn gassiness tends to improve after 6 to 8 weeks of age,” he says. “Be patient and trade off when you can, so no parent is ‘on duty’ all the time.”

Once you give your baby solids, the color, smell, texture and frequency of the stool changes. It will become a bit thicker with a stronger odor, and the color might depend on the food the baby ate.

How often a baby has a bowel movement can vary as well. Bowel movements can occur multiple times a day or once every few days, and both situations are normal.

“Sometimes a baby can have a bowel movement every three or four days and they are fine. It doesn’t necessarily mean that they are constipated. If the baby is showing happy behavior, feeling well and wetting diapers, there’s no cause for concern,” Dr. Baler says. “The way the gut moves and responds to food in the digestive system changes as a baby continues to grow.”

Common Digestive System Problems in Babies

Here are some of the most common digestive problems a baby might experience in the first year of life, according to Dr. Pickens and Dr. Baler.

Colitis is when babies are exposed to a protein in their diet that causes an irritation in their intestines. For breastfed babies, these proteins are in what the mother usually drinks or eats. They are also found in formula. The usual suspects are cow’s milk, soy and eggs. Symptoms include fussiness, gassiness and blood in the stool.

Intolerance to the mother’s diet is also fairly common in breastfed babies. If baby is gassier and fussier than normal, he or she could be having a reaction to something Mom ate.

Constipation in children can be caused by a range of problems including the use of certain medications, poor health or a lack of proper nutrition. Symptoms include hard, dry stools, straining more than normal to have a bowel movement, belly pain and bloating.

Gastroesophageal reflux disease (GERD) is when a normal behavior for babies—spitting up—comes with abnormal signs and symptoms, including poor weight gain and pain. Rarely, some babies gag and wheeze. If a baby seems happy and comfortable and is gaining weight, he or she might experience reflux (spitting up), but it doesn’t rise to the level of GERD.

Allergic reactions like a rash or hives are seen when a baby or toddler is having a reaction to something in his or her diet. The eight most common allergenic foods are milk, eggs, fish, shellfish, tree nuts, peanuts, wheat and soybeans.


If you’ve noticed your child having digestive system problems, contact your doctor or find one near you.