4 Reasons Tomatoes Can Upset Your Stomach

Tomatoes are a popular and versatile fruit (yes, fruit!) packed with nutrients like vitamin C and antioxidants. But for some people, tomatoes and related foods like tomato soup or sauce can lead to an upset stomach or other digestive symptoms like diarrhea.

Here are four reasons why tomatoes can cause tummy troubles and how to deal with it.

A food intolerance, according to the Mayo Clinic, is a reaction to a food similar to an allergy, but much less severe and not life-threatening — and it comes from the digestive system.

Some people just don't break down certain foods that are on the FODMAP list well, and that causes GI tract havoc.

FODMAPs (which stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols) are short-chained carbs that include fructans, lactose, fructose, sorbitol and mannitol, according to Harvard Health Publishing. These types of foods are notorious for causing upset stomach.

Tomatoes, unfortunately, are on the FODMAP list. They contain fructose, a natural sugar, according to Food Intolerance Diagnostics, and some people have fructose malabsorption or fructose intolerance.

The poorly digested fructose gets fermented by gut bacteria, says Ray Scott Daugherty, MD, who specializes in treating all colorectal diseases, which can lead to upset stomach symptoms including:

• Cramping and gas pains
• Diarrhea
• Constipation

Poor absorption of fructose is thought to be one of the dietary triggers for irritable bowel syndrome, and could be the reason why tomatoes give you diarrhea.

But keep in mind that a little tomato here and there may be fine.

"Small amounts of tomatoes may not cause a problem, but where some people get tripped up is with canned tomatoes or other tomato-based products like ketchup and pasta sauce," says dietitian Kristin West RD, LDN.

"These other products tend to have additives like high-fructose corn syrup or garlic, and that can take you into the high-FODMAP zone," she says.

So if you were wondering why tomato sauce gives you diarrhea or hurts your stomach, these ingredients could be to blame. Tomato soups and juices can also have various additives your stomach doesn't agree with, so don't forget to read labels.

‌Fix it:‌ If symptoms become problematic, it's best to have your doctor or a dietitian help you plan a diet around your restrictions so you can avoid upset stomach and diarrhea after eating tomatoes.

A food allergy can be a serious, potentially life-threatening condition. About 32 million Americans have one, according to Food Allergy Research & Education.

When you're allergic to a food, per the Mayo Clinic, your immune system mistakes the food (or something in the food) as harmful and goes into overdrive.

A small 2013 study in the ‌Journal of Investigational Allergology and Clinical Immunology‌ concluded that tomato allergy happens from an overreaction to certain proteins in the fruit.

People who are allergic to birch pollen may also be at higher risk for a tomato allergy because the main protein in birch pollen is similar to the protein in tomatoes, according to the European Centre for Allergy Research Foundation.

In response to these proteins (the allergens), antibodies, histamines and other chemicals are released into the bloodstream, which cause allergy symptoms.

According to dietitian Ashley Kravitz, RD, owner of Nutrition Specialists of New Jersey, these symptoms might include the following on the skin or mouth:

• Tingling
• Itching
• Numbness
• Redness

It's also possible that an allergy to tomatoes does cause diarrhea and other symptoms similar to those of fructose intolerance, she says, such as:

• Abdominal cramps
• Nausea
• Vomiting
• Diarrhea

‌Fix it:‌ It can be easy to confuse a food allergy with a food intolerance. If you have any of the above symptoms after eating tomatoes, see your doctor or an allergist, who can help you figure out the root cause.

Unfortunately, eating too many tomatoes can cause heartburn.

Heartburn, according to the Cleveland Clinic, is a symptom of acid reflux. It's an uncomfortable burning sensation in your chest due to an irritated esophagus that's caused by stomach acid. It can happen at any time, but it's usually worse soon after you eat.

"Many people experience heartburn after consuming tomatoes because of their strong acidity. The human GI tract produces gastric acid to break down foods that are sitting in your stomach, and when you consume acidic foods such as tomatoes, it can cause heartburn to act up," Kravitz says.

The discomfort may feel like an upset stomach, but the pain could actually be coming from an irritated throat. Other symptoms of acid reflux can include:

• Coughing
• Problems swallowing
• The feeling of food caught in your throat
• Sore throat
• Hoarse voice
• Vomiting

‌Fix it:‌ Heartburn can usually be managed with over-the-counter meds and other acid reflux remedies like eating smaller portions and remaining upright for a couple hours after eating. If necessary, though, your doctor can prescribe something stronger.

Food poisoning happens when you eat food contaminated with bacteria or their toxins, parasites or viruses, according to the Gastrointestinal Society.

Tomatoes can become contaminated with ‌Salmonella, Shigella,‌ or ‌Escherichia coli (E. coli)‌ during their growth in soil, or during harvesting, processing, storing, shipping or final preparation.

And food poisoning from tomatoes can cause diarrhea, along with upset stomach and the following other symptoms:

• Diarrhea
• Fever
• Vomiting
• Stomach cramps
• Dehydration

Botulism is a serious type of food poisoning that's caused by a toxin that attacks the nerves in your body and can lead to paralysis, per the Centers for Disease Control and Prevention, but can also induce stomach issues such as vomiting, nausea, diarrhea and stomachache.

People who eat home-canned tomato sauce are at risk for botulism due to the improper canning of overripe or spoiled tomatoes, under-processing and incomplete seals, per Colorado State University.