The Reasons for Diarrhea After Eating Junk Food

Processed foods may have a negative impact on your digestive system.
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If you've ever wondered whether eating highly processed food or food from a fast-food restaurant could cause you digestive upset, the answer is yes. As the old adage says, you are what you eat. So if you're feeling lousy, it might be due to what you've been eating.


Digestive upset could include diarrhea — watery, loose bowel movements that can send you to the bathroom with unwanted frequency. Diarrhea can have many causes, ranging from viral and bacterial infections and parasites to diseases such as Crohn's or ulcerative colitis, according to the U.S. National Library of Medicine. However, diarrhea can also be quite literally a byproduct of the foods we eat.

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"Any sort of processed foods, whether it is fast food or prepackaged food, can wreak havoc on a person's gut health," says Will Cole, DC, a functional medicine practitioner and senior clinical director of the Cole Natural Health Centers in Monroeville, Pennsylvania.


"Ultimately, these foods contain a variety of unnecessary added ingredients that can contribute to a lack of bacterial diversity, a compromised gut lining — also known as leaky gut — and chronic inflammation," he notes. "This can contribute to symptoms such as diarrhea, constipation, bloating and gas."

Fast Food or Highly-Processed Food?

Processed foods are often generically referred to as "junk" food or fast food. These are foods that have had other ingredients added to them during their preparation and packaging, according to the Harvard T.H. Chan School of Public Health. All these extra ingredients are called additives — not just preservatives but also artificial flavors and colorings, sugars, fats, salts and even nutrients like vitamins.


Technically, the majority of all packaged food items have been processed in some form. However, the level of processing can vary from minimally processed — foods that have been only slightly altered to preserve them (this can be as basic as canning, freezing, drying or baking) — to highly processed, where additives are used to increase taste, texture, color and shelf stability beyond minimal preservation, plus the addition of ingredients such a salt for taste, for example.

"Fast food is generally high in a combination of ingredients that, even on their own, can contribute to digestive distress in high amounts, such as gluten, bad oils, sugar, artificial sweeteners and other chemicals and preservatives," says Dr. Cole. "Many people go years with hidden sensitivities to these foods without even realizing it because they think the way they feel or their symptoms are 'normal' since they may be common among the general population."



According to Amber Romaniuk, a certified holistic nutritional consultant based in Calgary, Canada, a highly processed/fast food intake can also have a negative impact on the gut flora in the large intestine.

"Healthy gut flora support proper digestion, production of some B-vitamins, which are important for energy, and proper bowel movements," she says. "Gut flora and our mood are highly connected, so the more refined sugars you take in (which are unhealthy bacteria's food source), the more the unhealthy bacteria overtakes the good, which can leave you feeling bloated, heavy, brain-fogged, tired and irritable."


Does Fast Food Cause Diarrhea?

According to Romaniuk, some people do experience diarrhea after eating such foods. "That could be from serious food allergies, like having celiac disease and having cross contamination of gluten," she says. "Artificial sweeteners disrupt the gut bacteria and can trigger diarrhea. If you aren't used to eating highly spiced foods, spicy fast food can trigger it as well."


"If you find you are sensitive to any particular foods, like wheat or dairy, this can trigger diarrhea as the body sees the food as a stressor and wants to eliminate it from the body as soon as it can," she adds. "The poor quality saturated fats that foods are deep-fried in also are a struggle for the body to break down, which can lead to passing through the digestive system too quickly."




Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.

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