Why Does Fiber Make Me Sick?

Fiber is a kind of carbohydrate that is not absorbed by the body. Although fiber is an important part of the diet, some people feel ill or develop discomfort when they consume foods that are high in fiber. If you feel sick after eating fiber, there are ways you can help your system adjust to high fiber foods.

Woman having stomach cramping and discomfort. (Image: champja/iStock/Getty Images)

Fiber and Gas

If you feel sick after consuming high fiber foods, it is probably because you are developing intestinal gas. Your intestines naturally contain some bacteria that survive by breaking down undigested food. When you consume fiber and other substances that are hard or impossible for your digestive tract to break down, these bacteria metabolize the fiber. A byproduct of this process is the production of gases such as carbon dioxide and methane.

Symptoms of Intestinal Gas

Consuming a large amount of fiber can increase your intestinal gas production. This can cause you to feel bloated or develop abdominal cramps, as the gas will swell in your intestines. When the gas leaves your digestive tract, it may cause flatulence or belching. Eating a lot of fiber can also cause diarrhea. These symptoms are generally fairly mild and are not indicative of serious health problems, but they can cause significant discomfort.

Types of Fiber and Effects

Not all types of fiber have the same effect on your digestive tract. Insoluble fiber, which can be found in wheat bran and some vegetables, passes through your digestive tract essentially unchanged. Because the bacteria in your colon do not significantly break down this kind of fiber, it produces little gas. Soluble fiber, on the other hand, swells to form a gel in your digestive tract and is usually responsible for intestinal gas, the National Institute of Diabetes and Digestive and Kidney Disorders notes.


If you frequently feel sick after eating fiber, reducing your fiber intake may relieve your symptoms. After a short break from high fiber foods, gradually add them back into your diet, as this will give your digestive tract and bacteria time to adjust to higher fiber foods. Over-the-counter natural enzyme products are available that can be added to high fiber foods to reduce intestinal gas production.

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