Open Gut Syndrome: How Does It Affect Solid Food Introduction?

Open gut syndrome is a theory claiming that the baby’s intestine has small gaps that let substances pass directly into the bloodstream. Accordingly, the small intestine lining cannot distinguish solid food and bacteria. The spaces between the cells are large enough to allow macromolecules like whole proteins to pass into the blood. This leads to digestive problems that can be harmful to infants. 

There is no substantial evidence to prove or refute the open gut theory. Until then, it remains a widely popular online myth. However, knowing the concept behind it may help parents weigh in on the proper timing of introducing solid foods to babies. 

Causes of the open gut syndrome

The intestine has a thin and permeable lining or gut barrier, critical in filtering nutrients from food.

It lines the GI tract and separates food and bacteria to prevent them from entering the bloodstream. 

Sometimes, the gut barrier is compromised so that it cannot effectively filter harmful substances that leak into the bloodstream. As a result, the open gut is also called the virgin gut or leaky gut syndrome.

The causes of the open gut syndrome are:

1. Immature digestive system

From the time the baby is born, the digestive system is not yet intact.

Newborn guts are permeable or open to allow easy passage of nutrients from breast milk.

The permeability decreases as he gets older, and according to a published study, closure happens when babies are only a month old. The closure is faster in breastfed babies than those fed with adapted or hypo antigenic (HA) formula.

Past research, however, concluded that the open gut closes starting from 4 months until 5 years of age. 

2. Imbalance gut microbiome

Leaky gut in infants happens due to a lack of digestive enzymes and an imbalance of the gut microbiome. The gut microbiome is the collection of bacteria, viruses, fungi, and other microorganisms in the GI tract.

When the baby first ingests milk, it jumpstarts the function of the digestive system. But, the gut microflora is not yet thriving at its best by that time. 

Digestive enzymes like amylase, lipase, and protease are also not very equipped to digest food. In adults, leaky gut is managed by taking supplemental enzymes and allowing it to heal.

In infants, the digestive tract copes up on its own as the baby matures and resolves gut issues. Breast milk plays a big role in regulating bacterial levels and its healthy balance in the gut. 

3. Trauma to the intestinal wall 

Inflammation of the small or large intestine causes intestinal trauma. In infants, it may be due to the disruption of healthy bacteria in the gut.

Food additives, allergens, stress, and chemicals can destroy the good bacteria in the stomach and reduce the mucous in the intestinal wall leading to inflammation.

The inflammation breaks the gut barrier, and substances that are not allowed in the bloodstream now easily pass into it. 

4. Medication

Antibiotics and medications throw off the balance of the gut microbiome and cause a temporary period of digestive upset. Maternal antibiotics also affect infant gut microbiome diversity, especially in breastfed babies.

Most medicines are harmless while nursing, but some medications transferred into the breastmilk can upset and inflame the baby’s tummy. 

Symptoms of the open gut syndrome

An infant girl is crying while she is being pushed in a baby stroller

Unfortunately, there is no definitive test to diagnose open gut and intestinal permeability. While imaging tests are available in adults, the condition is harder to rule out in infants. 

Allergies and food sensitivities are probably the biggest links to leaky gut, especially in babies born to a family with an allergy history.

Babies with gut issues are likely to experience symptoms like:

  1. Tummy pain
  2. Irregular bowel movement
  3. Frequent diarrhea or constipation
  4. Nausea and vomiting
  5. Dehydration

How does open gut syndrome affect solid food introduction?

Experts can argue about the best timing for introducing solid food in babies.

However, whether it is as early as 4 months or to wait until six months, the baby’s developmental readiness is still the most critical factor.

A baby is developmentally ready to eat when he can sit and support himself and swallow liquid without choking or pushing it back. 

When the baby is 4 to 6 months old and has an open gut, breast milk antibodies linger in the GI tract. It is what provides passive immunity, which reduces the likelihood of allergic reactions. Thus, early allergen introduction becomes more beneficial in reducing allergic reactions. 

So if your baby seems to be ready for food by 4 months, it is okay to grab that window of opportunity. Introduce solid food while he has that tolerance and passive immunity.

Starting him early helps make up for most of the nutrients he needs that exceed what milk can provide. His exposure to flavors also makes feeding more efficient and reduces food aversion. 

Treatment of the open gut syndrome

The permeability of the intestinal lining improves over time and completely resolves gut issues.

Children commonly have digestive problems, so don’t worry about recurring tummy issues. These GI disorders like reflux, GERD, diarrhea, constipation, and colic will go away when they reach six months of age. 

There is no quick and instant solution to digestive problems. But, your pediatrician may offer formula milk modification if you are not breastfeeding. He may recommend gripe water and Zantac to alleviate stomach discomfort.

For your baby’s health and wellness, always consider the nutritional advice of a healthcare expert. Ask about starting your baby with solid foods before the sixth-month mark if you think your baby is very ready for it. 


My baby will not take solid food at eight months, what should I do?

From six months, babies need to be introduced to solid food for growth support and development.

Talk to your pediatrician if your little one resists food at eight months for supplementation. And, be patient as it may take a few more tries before babies learn to like their food – keep trying. 

How to introduce food to determine food allergy?

In practice, pediatricians recommend giving your baby one food at a time for three to five days before trying another. It is easier for you to spot if your child is sensitive to that particular food.

Besides, the first solids are not about how much or how many foods your baby can take. It is about introducing them to food textures and flavors. 

When can I introduce cow’s milk?

Cow’s milk contains proteins and minerals that are hard for an immature tummy to handle.

Cow’s milk is only advisable in babies beyond 12 months. Although it is healthy and nutrient-dense milk, giving cow’s milk early risks babies to intestinal bleeding. 


Open gut syndrome is a widespread theory that points out a baby’s immature digestive system and its possible relation to allergies.

All babies are born with a leaky gut that improves depending on the growth of gut microflora. Without underlying organic diseases, open gut syndrome does not need medical intervention.

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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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