Going against the grain
Yes, it’s possible to eat too much fiber, and the results can be explosive.

Fiber is vital for a healthy digestive system. It facilitates fermentation and gas formation, and helps improve the bulk and regularity of bowel movements. In addition, a high-fiber diet can help with the regulation of lipid and blood pressure levels, diabetes control, and weight maintenance. Fiber is the food for the human microbiome (the 100 trillion organisms that live within us) that is so important for our overall health.

There is about a 15% to 30% reduction in all-cause and cardiovascular-related mortality upon comparing subjects who ate the most vs least amounts of dietary fiber.

The consumption of food rich in fiber also decreased the frequency of heart disease, stroke, type 2 diabetes, and colon cancer by 16% to 24%. In other words, for every 1,000 subjects, there were 13 fewer deaths and 6 fewer cases of coronary heart disease among those who ate fiber-rich foods.

Total deaths and incidences of coronary heart disease, type 2 diabetes, and colon cancer dropped by 5% to 27% for every 8 g of fiber consumed daily. Furthermore research has observed an increase in protective benefit in terms of stroke and breast cancer. Eating 25 g to 29 g of fiber daily provided adequate protection against disease. However, higher intake of dietary fiber could provide greater benefit, according to current research findings.

But is it possible to get too much of a good thing? In my practice I have only seen a few people that have been taking in to much fiber but a lot of patients taking in way too little dietary fiber.
As with most everything, moderation of this carbohydrate is key. Eating too much fiber (> 70 g daily)—as is common with whole- or raw-food diets—can result in you making a beeline for the bathroom, as well as other uncomfortable side effects.

Fiber requirements

The American Heart Association recommends fiber intake from a variety of foods. Total dietary fiber consumption should range from 25 to 30 g daily from food—not supplement—sources. More specifically, the Academy of Nutrition and Dietetics recommends 25 g of fiber per day for women and 38 g a day for men. Adults aged 50 years and older should consume less fiber, at 21 g per day for women and 28 g per day for men. Pregnant or lactating women should eat 28 g of fiber per day.

Types of fiber

Fiber exists in two forms: soluble and insoluble. Even though the body can’t absorb either form, they are both necessary. Soluble fiber breaks down in water and forms a gel that keeps feces soft while slowing digestion. Insoluble fiber does not break down, instead adding bulk to stool and decreasing transit times. The body needs both types of fiber, so most research simply focuses on total fiber intake.

Too much fiber

Symptoms of eating too much fiber can include bloating, gas, cramping, constipation, diarrhea, reduction in appetite, and early satiety.
One of the negative side effects of overconsumption of fiber includes the underabsorption of key micronutrients, since fiber binds with minerals, such calcium, iron, magnesium, and zinc. Furthermore, high-volume meals can make it difficult to keep up energy intake, resulting in weight loss or lack of weight/muscle gain. Lastly, intestinal obstruction can occur in the setting of copious fiber intake but limited fluid intake.

What to do

If you are consuming too much fiber in your diet, try the following:

  • Stop eating products with added fiber, such as high-fiber cereal bars or high-fiber breads
  • At mealtime, replace high-fiber foods, including grains, with lower-fiber alternatives
  • Avoid foods that cause bloating, such as sugar-free gum and candy
  • Choose cooked over raw veggies
  • Increase fluid intake
  • Exercise more

In one prospective, longitudinal case study involving 63 patients with idiopathic constipation, reduced fiber intake decreased constipation, bloating, and stomach pain, and increased the frequency of bowel movements.
Specifically, during a period of 6 months, 41 patients were on a no-fiber diet, 16 were on a reduced-fiber diet, and 6 continued on a high-fiber diet due to personal or religious factors. Participants who stopped their dietary fiber intake completely went from having 1 bowel movement every 3.75 days to having 1 per day. In those who reduced their fiber intake, bowel movement frequency went from 1 every 4.19 days to 1 every 1.9 days.

High-fiber foods

Here is a list of high-fiber foods with values rounded to the nearest 0.5 g:

Fruits

Serving size

Total fiber

Raspberries 1 cup 8.0 g
Pear 1 medium 5.5 g
Apple, with skin 1 medium 4.5 g
Banana 1 medium 3.0 g
Green peas, boiled 1 cup 9.0 g
Broccoli, boiled 1 cup chopped 5.0 g
Potato, with skin, baked 1 medium 4.0 g
Sweet corn, boiled 1 cup 3.5 g
Cauliflower, raw 1 cup chopped 2.0 g
Carrot, raw 1 medium 1.5 g
Spaghetti, whole wheat, cooked 1 cup 6.0 g
Barley, pearled, cooked 1 cup 6.0 g
Bran flakes 3/4 cup 5.5 g
Oat bran muffin 1 medium 5.0 g
Oatmeal, instant, cooked 1 cup 5.0 g
Popcorn, air-popped 3 cups 3.5 g
Brown rice, cooked 1 cup 3.5 g
Bread, whole wheat 1 slice 2.0 g
Bread, rye 1 slice 2.0 g
Chia seeds 1 oz 10.0 g
Almonds 1 oz (23 nuts) 3.5 g
Pistachios 1 oz (49 nuts) 3.0 g

 

Finally, remember that fiber is a really important part of the diet. If a person feels sick from eating too much fiber, then a low-fiber diet may be a good idea for some time, with limited amounts of fiber gradually re-introduced into the diet but very few people in my experience take too much fiber from real foods.
I have often recommended increasing dietary fiber intake and replacing refined grains with whole grains to curb the risks associated with a gamut of diseases.
Always discuss any changes in your diet with your primary care provider. Thanks