Is Eating Too Much Fiber Harmful? What You Should Know

Eating too much fiber – good or bad?

According to the Dietary Guidelines for Americans, 2020-2025, there is a concern with fiber since it is often under-consumed. If it is not eaten in adequate amounts, health problems can result. The Dietary Guidelines for Americans, 2020-2025, explain most men and women (97% and 90% respectively) do NOT meet daily requirements for this nutrient. So, eating extra fiber should be okay, right? Let’s see.

Fiber explained

Fiber is a dietary component naturally found in plant foods – fruits, vegetables, grains, nuts, and seeds. As humans, we cannot digest or absorb this after we eat it.²

You can actually see fiber in certain foods. For instance, think about those white pieces on orange slices, the stringiness of a sweet potato, or even fruit and vegetable skins.

There are two types of fiber – insoluble and soluble, and each has its benefits. Most foods contain both but vary in ratios of one to the other.

Also, prebiotic foods are mostly fiber sources (not all types of fiber are considered a prebiotic, though). Prebiotics are foods that feed the beneficial bacteria in our digestive tract.³

Insoluble fiber

Insoluble fiber is found in foods that don’t attract water. This type of fiber helps to increase stool volume or “bulk.” Additionally, it aids in moving foods through the gastrointestinal tract.

Insoluble food sources include components such as cellulose, hemicellulose, and lignins.⁴ Basically, these are different structural parts that make up plants.

Food sources: oats, wheat and wheat germ, lentils, canned kidney or lima beans, raw white beans, eggplant, raw carrots, raw broccoli, apple with skin on it, kiwi, peanuts and almonds, coconut, flaxseed, sesame seeds⁴

Soluble fiber

Categories include pectins, gums, and mucilages.⁴ Soluble fiber sources form a gel-like substance because they draw in water. They contribute to adding volume to stool because of their water uptake and can also help lower LDL cholesterol levels in the body.

Food sources: oatmeal, berries, sweet potatoes, avocado, raw white beans, flaxseed, sesame seeds, pears⁴

Importance of adequate fiber in the diet

Fiber can improve our health through the following processes:

• Carries LDL (“bad”) cholesterol away from our organs and out of the body
• Slows down processing of food in the body which controls blood glucose levels
• Keeps us full at meals/snacks – this helps to avoid overeating and possible weight gain
• Regulates bowel habits
• Maintains the good bacteria in our digestive tract

Fiber and Nonalcoholic Fatty Liver Disease

With all of the ways fiber can keep us healthy, most of these also relate to management of nonalcoholic fatty liver disease (NAFLD). Increased consumption of fiber can actually protect you against this condition.⁵

Excess intake of simple carbohydrates, such as refined grains, can lead to fat buildup in the liver and body. Research also shows these foods contribute to a more advanced stage of fibrosis.⁶

Prebiotics and NAFLD

Prebiotic consumption is beneficial for NAFLD as well. When certain bacteria relocate in the body, they could cause inflammation and increase insulin resistance.⁶ Eating prebiotic foods can alter our gut microbiome (the “home” for bacteria in our GI tract) for the better; it specifically may be able to treat nonalcoholic steatohepatitis (NASH).⁶

Daily fiber recommendations

Below are the recommended daily fiber intake goals by age and gender, according to the Dietary Guidelines for Americans, 2020-2025. The total amount is indicated in grams.

Females:

• 14-18 years old: 25 grams
• 19-30 years old: 28 grams
• 31-50 years old: 25 grams
• 51+ years old: 22 grams

Males:

• 14-18 years old: 31 grams
• 19-30 years old: 34 grams
• 31-50 years old: 31 grams
• 51+ years old: 28 grams

Because everyone has individual needs, there is a more precise method you can use to determine yours. It is recommended to have 14 grams of dietary fiber for every 1,000 calories consumed.⁸ Here are the steps and equation to figure out your daily fiber requirements:

Step 1: Divide # of calories you consume in a day by 1,000.

Step 2: Take the number you got as a result from Step 1 and multiply it by 14.

Example:

1500 / 1000 = 1.5

1.5 x 14 = 21 (grams per day)

Symptoms of eating too much fiber

Consuming too much fiber can lead to stomach upset. Specifically, digestive symptoms like stomach pain, gas, and bloating can happen. If you are eating too much insoluble fiber, it could lead to diarrhea due to the increased transit of food.

Your body has to adjust to a higher amount of fiber; therefore, add it in over time.

Starting to use fiber supplements may also temporarily cause symptoms.

Symptoms of eating too little fiber

Common gastrointestinal symptoms of too little fiber can include constipation, bloating, or pain. Particularly, constipation can occur because there is not enough fiber to move food along the digestive tract. Constipation means having equal or less than three bowel movements per week.⁹

Over time, inadequate fiber intake can cause or worsen health problems such as weight gain, nonalcoholic fatty liver disease, and elevated LDL cholesterol and triglyceride levels. If a diet lacks fiber, odds are it includes a lot of refined grains instead. As a result, insulin resistance can increase.

Increasing fiber in your diet

Adding too much fiber quickly can cause side effects opposite of what’s intended. Stomach pain, gas, and bloat may arise. Increasing fiber intake over time is the best way to avoid these symptoms.

According to Harvard Health Publishing, it is recommended to increase your fiber intake by one serving at a time. Include the additional serving every day for a week, and if you do not have any symptoms, go ahead and add another serving in the second week. Continue with this method until you reach your intended fiber goal.

Proper hydration

With more fiber, it is important to drink plenty of water throughout the day. Sixty-four ounces of water is recommended daily (or more, depending on individual needs).¹⁰ Staying properly hydrated helps you to keep fiber moving through the digestive tract and avoid any discomfort/symptoms.¹⁰

Fiber and the Nutrition Facts label

The Nutrition Facts label can be overwhelming. There are several things to look at. I find one part of the label most useful, though, in evaluating different nutrients.

Let me start by saying the Percent (%) Daily Value is my favorite part of the label because it is helpful in many ways (…yes, I have a favorite part of the label. Nutrition nerd here!). It is on the right side of the nutrient list.

This percentage reflects a 2,000 calorie diet. While everyone has individual requirements, it is best used as a guide. Instead of having to remember/track exact amounts of fiber (or other components), use the following rules:

If the percentage is 5% or less, the item is “low” in the nutrient.

If the percentage is 20% or above, the food is “high” in that nutrient. We ideally want a higher percentage for fiber.

Not all numbers fall in those categories. Even if it is in the middle, you have a good idea of whether the product is high or low in fiber. This tool also is good for comparing products.

Fiber supplements

Whenever possible, it is best to get fiber from food sources rather than supplements. With the consumption of food, you are not only getting fiber but other nutrition as well. Fiber supplements are beneficial, though, if a food allergy, intolerance, or food preferences prevent someone from getting adequate intake.

There are different types of fiber supplements sold as liquid, powder, gummies, or caplets. Based on the medical issue at hand, one type may be preferred over another. It’s recommended to first speak with your doctor since fiber supplements can worsen stomach or bowel issues that already exist; they can also interact with prescription or over-the-counter medications.¹¹

High fiber snacks: Are Fiber One^™ bars healthy?

Taking in too much fiber is possible if foods with added fiber are consumed in excessive amounts. It is okay to go above your daily fiber goal, but the source matters.

Inulin, specifically in the form of chicory root, is the added fiber in Fiber One^™ bars. It is found in some processed foods to enhance flavor without contributing as many calories as sugar or fat usually would.¹²

This soluble fiber, like others, can reduce constipation and contribute to bulking of stool. In addition, inulin can be helpful for people who suffer from Irritable Bowel Disease (IBD).¹²

Non-digestible fibers like inulin can often lead to gas production because of a process in the body called fermentation. Studies that assessed inulin intake (as chicory extract) showed 5 grams/day was a well-tolerated amount. Higher doses led to some participants experiencing flatulence. ¹²

A closer look at the product

Let’s check out a Fiber One^TM product. Chicory root is first in the list of ingredients. These lists on labels go in order from most to least, which means the highest content of any ingredient in this bar is the chicory. For this reason, it is not uncommon to experience some gastrointestinal distress as a result.

This bar is also highly processed. However, if you choose to eat it rather than a higher fat/sugar alternative, it may be a good idea to see how your body reacts by trying a smaller amount first.

Conclusion – Don’t overdo it!

As we now know, you can overdo it by eating too much fiber. This is unlikely to occur when trying to obtain it from food products alone. Yet, if too much is added into the diet at once, discomfort and other GI symptoms may occur until the body gets adjusted to the higher amount.

Increase intake slowly. If it is a bit much, you can reduce the additional amount and/or wait to increase further.

While it is ideal to meet your daily intake goals through food first, it may be necessary to supplement depending on the situation.

There are many wonderful foods high in fiber and other nutrients. Try pairing different foods together for a meal rich in nutrition that is sure to fill you up and fuel your day!

Fiber content of foods

Check out this list of various foods and their fiber content from the Journal of the Academy of Nutrition and Dietetics.¹³

References

1. https://www.dietaryguidelines.gov/
2. Nicola Veronese, Marco Solmi, Maria Gabriella Caruso, Gianluigi Giannelli, Alberto R Osella, Evangelos Evangelou, Stefania Maggi, Luigi Fontana, Brendon Stubbs, Ioanna Tzoulaki, Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses, The American Journal of Clinical Nutrition, Volume 107, Issue 3, March 2018, Pages 436-444, https://doi.org/10.1093/ajcn/nqx082
3. Holscher H. D. (2017). Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut microbes, 8(2), 172–184. https://doi.org/10.1080/19490976.2017.1290756
4. Dhingra, D., Michael, M., Rajput, H., & Patil, R. T. (2012). Dietary fibre in foods: a review. Journal of food science and technology, 49(3), 255–266. https://doi.org/10.1007/s13197-011-0365-5
5. Zolfaghari, H., Askari, G., Siassi, F., Feizi, A., & Sotoudeh, G. (2016). Intake of Nutrients, Fiber, and Sugar in Patients with Nonalcoholic Fatty Liver Disease in Comparison to Healthy Individuals. International journal of preventive medicine, 7, 98. https://doi.org/10.4103/2008-7802.188083
6. Perdomo CM, Frühbeck G, Escalada J. Impact of Nutritional Changes on Nonalcoholic Fatty Liver Disease. Nutrients. 2019 Mar 21;11(3):677. doi: 10.3390/nu11030677. 
7. https://www.dietaryguidelines.gov/sites/default/files/2021-03/Dietary_Guidelines_for_Americans-2020-2025.pdf
8. https://www.eatright.org/food/vitamins-and-supplements/nutrient-rich-foods/fiber#
9. https://www.mayoclinic.org/diseases-conditions/constipation/symptoms-causes/syc-20354253
10. https://www.health.harvard.edu/staying-healthy/how-to-get-more-fiber-in-your-diet
11. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/fiber-supplements/faq-20058513
12. Shoaib, M., Shehzad, A., Omar, M., Rakha, A., Raza, H., Sharif, H. R., Shakeel, A., Ansari, A., & Niazi, S. (2016). Inulin: Properties, health benefits and food applications. Carbohydrate polymers, 147, 444–454. https://doi.org/10.1016/j.carbpol.2016.04.020
13. https://jandonline.org/action/showFullTableHTML?isHtml=true&tableId=tbl2&pii=S2212-2672%2815%2901386-6