Soy Formula Poops – What Does It Look Like And When Should You Worry?

Soy formula-fed babies have poop that is firm with a tan or yellow color. Soy formula is often given to babies with digestive issues such as loose bowel and acid reflux. It contains a more digestible plant protein, which is beneficial for babies having problems breaking down cow’s protein. For a brief period, some babies may experience bouts of constipation as they transition to soy formula. But since it does not contain milk sugar or lactose, diarrhea rarely occurs when using soy formula milk.

If you want to transition your baby into soy formula, please check with your pediatrician first. The product is only recommended for babies older than six months.

Although it is vegan and a solution to reflux and milk protein sensitivity, it also has its downsides.

What does a normal baby poop look like?

The baby’s poop color, texture, consistency, and appearance are directly affected by his diet. Thus, a breastfed baby will have a different poo than a formula-feed one.

It also varies depending on the ingredients of the formula given. Cow-based, plant-based, and hydrolyzed formulas all differ. 

Age also affects the poop appearance, such that it is different in newborn babies, infants, and toddlers eating solid food. 

Newborn baby poop

The newborn baby’s first poop is called meconium. It is a tarry, greenish-black color with sticky mucus.

It can last about 2 to 4 days and change its appearance as the baby adjusts to milk feeding.

Despite its appearance, meconium has no distinct smell since it is mostly just mucus, amniotic fluid, and dead cells. 

Breastfeed baby poop

Breastfeed babies have yellow or slightly green poop with speckles that look like seeds – think about mustard.

It has a runny consistency that resembles diarrhea but is not very liquid and waterlogged. It is sometimes frothy and greenish, but this is nothing worrisome. It only means the baby is getting more foremilk than hindmilk.

To remedy this, you only need to feed your baby longer and start the session on the breast where you last fed. 

Formula-feed baby poop

Formula-fed babies have a tan, yellow or greenish poop with a thick and pasty consistency.

The color may sometimes have a cross of brown, tan-brown, or yellowish brown. The smell is a bit pungent, but it varies in every formula brand and basic ingredient used. 

Babies who take soy formula may have green or dark green poop because of its high iron content.

One of the disadvantages of soy formula is its ability to inhibit iron absorption. Thus, the WHO requires that soy formula be fortified with iron to compensate for its effect. 

Why do soy formula-fed babies have green poop?

Soy formula is mostly recommended for full-term babies over six months old with galactosemia and gastroesophageal reflux (GER).

It contains almost all of the nutrients and calories from regular formula milk. However, it lacks cow’s milk protein, contains half the fat content of formula, and is alkaline.

Soy formula is also high in aluminum, which inhibits calcium and iron absorption. 

To make up for the discrepancy, soy formulas are fortified with iron. But unlike the iron found in breast milk, those found in soy are not absorbed well by the body.

Too much iron gives off a greenish color to an almost black poop. You will also observe this if you are giving your baby an iron supplement

If your baby has black and tarry poop but is not taking soy formula or iron supplements, it is best to call your pediatrician.

Black poop is called melena, and it may mean blood in the stool.

Your baby’s pediatrician will check for possible stomach bleeding for causes other than the baby’s milk and food intake. 

How often should babies poo?

Mom is changing her infant baby's soiled diaper

The frequency of pooing in babies varies, so there is no exact gauge on how often they should go.

Breastfed babies tend to poop after they eat more than once a day. When a baby is formula-fed, he may go once a day or sometimes more often

Other infants, especially breastfed ones, don’t poop for a day or two or sometimes even for a week. Formula-feed babies may sometimes poop once every couple of days.

As long as your baby is eating, gaining weight, and acting fine, the frequency of his poop is not anything you should worry about. 

Soy formula and constipation

Soy formula is sometimes given to babies after a bout of diarrhea.

That’s because there might be a brief period when they cannot digest lactose in milk. Soy formula milk bulks up and hardens stool to help ease the baby’s digestive system. 

The problem is that it may also cause constipation.

As a home remedy, some moms rely on pear or prune juice to alleviate it. Still, it is wise to talk to your pediatrician before giving your baby anything. Juices are also only applicable for babies six months and older. 

When to call the doctor

Mom and her infant baby are at the pediatrician to get checked out after the baby's poop routine has been inconsistent.

Changes in the baby’s excretion cause too many pediatric appointments from worried parents.

From its display of color, changing consistency, and incomparability with babies their age, how would you know it needs medical attention?

  • Very loose and watery stool that does not resolve after a few days
  • Signs of dehydration
  • Blood or mucus in the poop
  • Solid and hard poop
  • Black poop 
  • Pale, grey, or white poop, which may mean biliary atresia 


Is soy formula the same as soy milk?

No, soy formula and soy milk are two different products. Soy formula contains soy protein and other ingredients for the developing baby’s needs.

Soy milk, on the other hand, is made of soybeans and water without the benefit of a baby’s nutritional needs. Thus, soy milk is only appropriate as an alternate milk source for toddlers but not entirely for primary feeding. 

How would I know if my baby is allergic to soy formula?

Abdominal pain, diarrhea, vomiting, and bloody stool manifest soy sensitivity.

Hives or itching, swelling of the body parts, wheezing, runny nose, and trouble breathing may also occur.

How can soy formula affect babies?

Soy formulas are strictly regulated to ensure that they meet the nutritional needs of babies. But there are ongoing concerns about their high aluminum and phytate levels.

Phytoestrogens in soy formula can potentially affect sexual development, immune resistance, and thyroid function with its estrogen-like activity in the body. 

It may also affect bone mineralization, especially in preterm babies and those with renal impairment. Before switching to soy formula, please ask your pediatrician first for sound advice on its benefits and drawbacks.

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Ann Marie is a licensed nurse in the Philippines. She experienced handling and assisting deliveries of newborns into the world. She also trained in labor rooms and pediatric wards while in nursing school - helping soon-to-be mothers and little kids in the process. Though not a mother by nature but a mother by heart, Ann Marie loves to take care of her younger cousins as well as nephews and nieces during her free time.

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