Why Does Cereal Upset My Stomach?

If you have stomach pain after eating cereal, several factors can contribute, such as overeating.

If it only happens occasionally, it’s likely not a cause for concern. But if it happens consistently, a digestive condition could be to blame, especially if you experience pain with milk.

For example, the inability to digest a sugar found in milk called lactose, a condition known as lactose intolerance, is a common cause of stomach pain. It’s also possible that something in your cereal, such as wheat or gluten, is the source of the problem if you have an allergy or intolerance.

It can be difficult to pinpoint the source of the discomfort on your own. If it occurs consistently, see your doctor to help determine the underlying cause. Here are four possible causes of stomach pain after eating cereal and milk.

1. Lactose Intolerance

Cow’s milk contains a sugar called lactose, according to Mayo Clinic. The digestive system uses an enzyme called lactase in the small intestine to break it down. Some people don’t have this enzyme, though.

If the lactase enzyme is missing, bacteria in the large intestine break down the lactose. This can cause gas, stomach pain, bloating, or diarrhea in some people.

Not everyone will have the same symptoms, and stomach pain may be the only symptom of lactose intolerance. Up to 50 million people in the United States have lactose intolerance, according to the Ann & Robert H. Lurie Children’s Hospital of Chicago.

2. Milk Allergy

The proteins in cow’s milk are a common allergen, particularly for young children and infants, according to the American College of Allergy, Asthma, & Immunology. Many children outgrow it, but it can occur through adulthood.

Unlike lactose intolerance, an allergy to milk can be life-threatening. The symptoms of a milk allergy, such as stomach upset, may be similar to those of lactose intolerance. Other symptoms typical of allergies may also be present, including:

• Itchy skin or hives
• Vomiting
• Blood in stool, especially in infants
• Anaphylaxis, a severe, life-threatening allergic reaction that causes difficulty breathing and can cause the body to go into shock

Seek emergency care immediately if you or your child have difficulty breathing after drinking milk.

3. Too Much Fiber in One Sitting

The cereal itself could be causing stomach pain. Fiber is a common ingredient in cereals. It’s important for digestive health, according to Mayo Clinic. But it can cause gas, bloating, and stomach pain if you eat a lot of it in one sitting, particularly if you’re not used to eating that much fiber on a regular basis.

According to the 2020–2025 Dietary Guidelines for Americans, adults should try to eat 28 to 34 grams of fiber each day.

If you’d like to increase how much fiber you eat, go slowly and drink plenty of water. Doing so can help your body adjust and minimize side effects like gas.

4. Intolerance or Allergy to Ingredients in Cereal

Other ingredients in cereal could potentially cause digestive problems, too. You may have a food intolerance, similar to lactose intolerance, or an allergy. Wheat, for example, is found in many cereals and is a common cause of food allergies, according to Cleveland Clinic.

An intolerance to gluten, a protein found in wheat, barley, and rye, can also cause stomach pain in some people, according to Cleveland Clinic. Other symptoms of a gluten intolerance may include:

• Gas or bloating
• Constipation or diarrhea
• Fatigue or brain fog
• Headache
• Joint pain
• Nausea or vomiting
• Skin rash

Another digestive condition linked to gluten consumption is celiac disease. Celiac disease is an autoimmune disease in which eating gluten causes damage to the small intestine. According to the Celiac Disease Foundation, some common symptoms include:

• Abdominal pain
• Constipation or diarrhea
• Nausea or vomiting
• Fatigue
• Headache or migraine
• An itchy skin rash with blisters
• Joint pain
• Nausea or vomiting
• Unintentional weight loss

Talk to your doctor if you suspect you have any of these conditions. Your doctor can evaluate your symptoms, make a diagnosis, and prescribe treatment.

Should You See a Doctor?

Stomach pain that occurs once or twice after eating cereal and milk could be due to overeating. As mentioned earlier, an isolated incident like that is generally not cause for concern.

If the problem occurs consistently, however, it’s best to get checked by a doctor, even if the symptoms are mild.

Your doctor can run tests to determine whether you have lactose intolerance or a more serious allergy to milk or one of the ingredients commonly found in cereal.

In some cases, a previously undiagnosed digestive problem, such as celiac disease, may be to blame.

The Takeaway

• Occasional discomfort after eating cereal might be due to factors such as overeating or consuming too much fiber in one sitting. Try gradually adjusting your dietary habits accordingly.
• If you frequently experience stomach pain after eating cereal, consider consulting a healthcare professional to rule out conditions like lactose intolerance, milk allergy, celiac disease, or gluten intolerance.
• Be attentive to severe allergic reactions like anaphylaxis after dairy consumption, which requires immediate medical attention.