You’ve probably been told to eat more dietary fiber by many well-meaning people including your doctor, but too much of a good thing could turn bad. Fiber makes you feel full for longer and it’s important for cleaning out your intestines. It promotes regular bowel movements and keeps your cholesterol levels in check. However, eating too much of it without drinking enough water leads to a variety of side effects, most of which are merely uncomfortable, but some of which are more serious.
Dietary fiber is a type of carbohydrate found abundantly in grains, fruits, vegetables and legumes such as peas and beans. Fiber is poorly digested, but it’s beneficial because it slows down digestion and absorbs water, toxins and cholesterol in your intestines. Women need between 21 and 25 grams of dietary fiber each day depending on their age, although most Americans typically get no more than half that amount. A lack of dietary fiber usually leads to constipation, loose stool and a greater tendency to snack between mealtimes. Over-indulging in fiber also causes symptoms.
Abdominal pain is probably the most common symptom of eating too much fiber. Insoluble fiber such as cellulose attracts water in your large intestine, which is good for bulking up stool and cleaning the bowels, but it can lead to constipation if your intestinal mucous membranes become dry. Not drinking enough water is the common culprit and it’s particularly pervasive in elderly women during the hot, summer months. Constipation creates intestinal pressure, bloating and lower abdominal pain that is often described as sharp or cramping. A complicating factor is gluten intolerance, which also causes abdominal pain. Gluten is a protein found in high-fiber grains such as wheat and barley. Severe constipation for much more than a week can become a medical emergency due to pain and blood toxicity.
Gas and Flatulence
Constipation or sluggish intestinal movement from over-consumption of fiber often leads to the production of gas and increased flatulence, which always seems to cause a little embarrassment. Carbon dioxide and sulfuric gases are produced because the friendly bacteria in your large intestine ferment the fiber that’s stuck or lingering there. Another complicating factor is eating too much fructose at one time, which is found in high-fiber fruits such as strawberries, oranges and melons. Partially undigested fructose sugar is also fermented by bacteria and produces gas. Gas build-up without flatulence quickly leads to abdominal pain. Gas and flatulence can also trigger diarrhea, especially if gluten intolerance or undigested fructose are additional factors.
For people who consistently consume more than 40 grams of fiber per day, reduced absorption of certain nutrients can be a problem. In particular, high fiber intake can interfere with the absorption of important minerals such as calcium, magnesium, zinc, iron and phosphorus. Soluble fiber such as pectin gets sticky in water, which is good for grabbing on to toxins, heavy metals and cholesterol-rich bile, but not so good when it sticks to minerals and prevents them from being absorbed. Furthermore, chronic constipation can lead to fecal impaction in the intestines, which prevents efficient nutrient absorption.
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw, et al.
- Public Health Nutrition: From Principles to Practice; Mark Lawrence and Tony Worsley
- Encyclopedia of Human Nutrition; Benjamin Caballero, et al.
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.