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Too Much of a Good Thing: The Side Effects of a High Fiber Diet

Wondering if too much fiber can hurt you? Read on to learn the side effects of eating too much fiber.
By 
April Panitz, MS, RDN, CDN
MS, RDN, CDN

Too Much of a Good Thing: The Side Effects of a High Fiber Diet

Fiber is everywhere these days. Heck, “Make Fiber Your Friend” is a slogan Amenta uses on some of its merch! Fiber deserves to have an excellent reputation because it has so many benefits: it helps to keep you regular, can aid in keeping you feeling full and satiated, and helps to regulate blood sugar. Fiber may also reduce your risk for heart disease and it’s been shown that it may provide protection against some cancers, including colon cancer.

Sounds fantastic, but does that mean you should eat as much fiber as possible? Can eating too much fiber be bad for you? Read on to learn the positive and negative side effects that eating too much fiber may have on your digestive tract.

What is Fiber?

Fiber is found only in plant foods and is a non-digestible carbohydrate. In layman’s terms, it's the part of plants that we eat that our bodies can’t digest or absorb. It can pass through the intestines relatively intact because we don’t have an enzyme to break it down (we’ve all seen corn in the toilet!). Fiber is often thought of as food with roughage or bulk, and this is why it can help to normalize bowel movements. But fiber isn’t just roughage or bulk. Fiber can be separated into two main types: dietary and functional fiber.

Dietary Fiber

Dietary fiber is the fiber that you eat from plants. It’s found in seeds, whole grains, fruits, vegetables, beans, legumes, and nuts. Some of the more specific names of dietary fibers include cellulose, hemicellulose, lignins, gums, pectin, fructans, beta-glucans, and resistant starches. 

Functional Fiber

Functional fibers are produced from isolated, extracted, or manufactured non-digestible carbohydrates. These have been shown to have beneficial effects on people and are added to foods and supplements to increase their fiber content. 

A few examples of functional fiber supplements are products like Metamucil, Benefiber, and FiberCon. Chicory root, inulin, pectin, gums, and resistant starches are examples of functional fibers added to foods to increase their fiber content, texture, and palatability. 

Physical and Chemical Properties.

Fiber can be further classified based on its molecular size, solubility, its viscosity, and its fermentability. It can sound “science-y” and can get very complicated because most plant foods contain fiber that fits in multiple categories (which is why working with an expert like a GI dietitian is so important!). Check out our Fiber 101 blog post to learn more.

The Benefits of Eating Fiber?

Fiber has many beneficial effects. At Amenta, we are always trying to stress the importance of having fiber at every meal and snack because it is just SO good for you. A recent review in  Nutrients highlighted many of fiber's benefits. It showed that high-fiber diets are associated with fewer metabolic diseases like diabetes, obesity, and cardiovascular disease. They demonstrated a preventative effect against cancer, specifically colon and breast cancer. High fiber diets are associated with eating more fruits, vegetables, and whole grains and are usually lower in fat and energy, which aids in weight control and leads to a more diverse microbiome.

Cardiovascular and Metabolic Health

Studies on specific types of fibers and their benefits were also highlighted in the Nutrients review and show the importance of fiber in terms of metabolic and cardiovascular health. Six grams of beta-glucans were shown to lower Low-density lipoprotein (LDL) cholesterol and overall cholesterol. Six grams of partially hydrolyzed guar gum with meals was shown to reduce postprandial (after eating) plasma glucose, postprandial insulin, and triacylglycerol levels. Ten grams of Arabic gum a day also had favorable outcomes, such as decreasing HbA1c levels (the three-month average blood sugar level) and decreasing fasting blood sugar levels. 

Gut Health

The breakdown and fermentation of fiber, which is determined by its solubility and viscosity, is another way in which fiber has positive effects. Bacteria in the large intestine ferment the fiber, which produces by-products of hydrogen, carbon dioxide, and short-chain fatty acids (SCFA)- acetate, propionate, and butyrate. Acetate is used in the production of cholesterol and fatty acids. Propionate is absorbed and processed by the liver and can inhibit lipogenesis (the conversion of fatty acids and glycerol into fat) and cholesterol production. Butyrate is used as fuel for cells of the colon and intestines, promotes beneficial bacteria, and helps maintain the integrity of the intestinal barrier. These SCFAs also stimulate intestinal motility, gastrointestinal transit time, and they activate the production of satiety hormones. 

Additionally, short-chain fibers that are prebiotics (like inulin) feed and boost the development of the microbiome, which can affect us in favorable ways! Prebiotic fibers have been shown to reduce the prevalence and duration of antibiotic-associated or infectious diarrhea. They have also been shown to reduce symptoms associated with Crohn’s disease and Ulcerative Colitis, protect against colorectal cancer, and reduce the risk of cardiovascular disease. Lastly, intake of prebiotic fibers has been shown to reduce allergies and promote the bioavailability of calcium, magnesium, and iron.

Poop Performance

Now that you’ve learned about some of fiber’s “unseen” or “hidden” side effects, let’s get into those that you can see and feel - how fiber affects your pooping. Different types of fiber can impact what happens in the toilet.

Soluble fiber is known to absorb water like a sponge. It forms a gel-like texture that keeps poop soft and formed, and it moves more slowly through the digestive tract. Soluble fiber can keep poop moist if you’re constipated and can also help it come together or become more formed if you suffer from diarrhea. 

Insoluble fiber is what we traditionally think of as roughage. Insoluble fiber can't be dissolved in water; you can see it when you poop. This type of fiber adds bulk to stool and speeds up the digestive transit. Insoluble fiber can be beneficial for constipation or if you suffer from slower transit. 

Can You Have Too Much Fiber? What are the side effects?

All of these benefits sound amazing, but is there a downside to eating too much fiber? Can too much fiber lead to unwanted side effects or be bad for you? Well, that depends. If you are not used to eating much dietary fiber- say you only eat ten grams a day- and you start eating thirty or forty grams of fiber per day, then you may experience side effects like bloating, distension, abdominal cramps, and diarrhea.

If you are not increasing your fluid intake along with the fiber, there could also be a risk of experiencing constipation. As fiber and other waste move along the colon, water is reabsorbed, making stool harder and drier. This could make it difficult to eliminate and also lead to dehydration down the line. Additionally, excess fiber consumption, especially from fiber supplements, may affect the absorption of essential minerals from foods, such as iron, zinc, and calcium, though no precise amount has been identified to know how much is too much.

Special Considerations for Fiber 

IBS

In patients with IBS, too much of certain types of fiber could lead to unwanted side effects. An excess of insoluble fiber could lead to pain due to their increased visceral hypersensitivity. This is because insoluble fiber mechanically activates the gut. It physically rubs against the intestines, which can cause pain. Additionally, certain fermentable fibers, the FODMAPs, can trigger symptoms of cramping, diarrhea, constipation, and excessive bloating and distension. Patients with IBS-D, or diarrhea-predominant IBS may not do well with lots of insoluble fiber as it can contribute to further loosening stools. As fiber has so many health benefits, it's important for someone with IBS to work with a dietitian to know which FODMAPs actually trigger symptoms and to make sure that they are getting adequate amounts of fiber that won’t hurt their bellies. 

Constipation

Too much fiber may lead to negative side effects in some people with specific types of constipation, including constipation that's a result of pelvic floor dysfunction, gastroparesis, or slow transit. In these situations, fiber can build up and result in bloating (pressure build-up), distension, gas, and sometimes even nausea. Imagine the gutters on your home being filled with leaves and twigs - you don’t remove them, and more and more debris starts to pile up. Now the water and smaller pieces of roughage are being blocked and cannot flow down the drain pipe to be released. This is how too much fiber (in this case, the leaves and twigs) can become impacted in your colon (gutters and drain pipe), contributing further to your stool burden (aka making you even more full of s%#!).

Small Bowel Obstruction

In those who have had a small bowel obstruction or intestinal scarring, too much fiber intake could lead to the formation of a phytobezoar. A phytobezoar is a dense mass of seeds, leaves, and other pieces that collect in the stomach. Those with these conditions should still consume the recommended intake of fiber; however, they should chew food extremely well (to a baby food consistency) or possibly think about modifying the texture of their fruits and vegetables. 

How Much Fiber Should You Have?

Now that we’ve gotten into what fiber is and how eating it can affect you, let’s dive into how much fiber you should be eating and why it’s so important to be eating fiber. 

Recommended Intake of Fiber

According to the Dietary Guidelines for Americans, 2020-2025, more than 90 percent of women and 97 percent of men are not meeting the recommended dietary fiber intakes. This is also in line with 85 percent of Americans not eating enough fruit, vegetables, and whole grains. For this reason, they have declared dietary fiber as a nutrient of public health concern as low intake of these plant foods is associated with an increased risk of chronic diseases. 

The recommended intake of fiber is based on the Dietary Reference Intakes, which are based on levels that were observed to reduce the risk of heart disease. It’s important to know that these amounts are based on the recommended energy intake and not from clinical fiber studies. The average amount recommended is 14 grams of fiber per 1,000 calories, or about 25 grams of fiber for women and 38 grams for men. Below are the recommended intake amounts based on sex and age, as well as the amount of fiber found in some fruits, vegetables, and grains.

Recommended Fiber Intake for Females

Age

2-3 years old: 14 grams

4-8 years old:  17 grams

9-13 years old: 22 grams

14-18 years old: 25 grams

19-30 years old: 28 grams

31-50 years old: 25 grams

50+ years old: 22 grams

Recommended Fiber Intake for Males

Age

2-3 years old: 14 grams

4-8 years old:  20 grams

9-13 years old: 25 grams

14-18 years old: 31 grams

19-30 years old: 34 grams

31-50 years old: 31 grams

50+ years old: 28 grams

Lists of High Fiber Fruit, Vegetables, and Grains

Fruit

Raspberries: 8g

Blackberries: 8g

Blueberries 4g

Strawberries: 3g

Cherries: 3g

Apricots: 3g

Nectarines: 2g

Peaches: 2g

Plums: 2g

Cantaloupe: 2g

*grams per cup

Vegetables

Black Beans: 16.6g

Chickpeas: 12.5g

Kidney Beans: 11g

Butter/Lima Beans: 9g

Green Peas: 9g

Collard Greens: 8g

Artichoke: 7g

Broccoli: 5g

Spinach: 4g

Green Beans: 4g

Okra: 4g

Swiss Chard: 4g

Asparagus: 4g

Sweet Potato (1 med): 3.75g

Corn: 3g

Zucchini: 2g

Tomatoes: 2g

*grams per cup

Grains

Pearled Barley: 6g

Quinoa: 5g

Buckwheat/Kasha: 4.5g

Oatmeal: 4g

Brown Rice: 3g

Millet: 2g

Couscous: 2g

White Rice: ~1g

*grams per cooked cup

*All fiber amounts from USDA Food Data Central 

How to Increase Your Fiber Intake & Avoid Side Effects

While we don’t like to call anything a miracle ingredient or a superfood, fiber, especially dietary fiber, is one component of foods that can provide amazing benefits. It helps to keep you regular, helps you to feel satiated, can aid in blood sugar regulation, and feeds your microbiome. Fiber has also been shown to be protective against heart disease and some cancers. While some may experience initial side effects when increasing their fiber intake, overall, these are usually mild and will go away once the body gets used to it. 

If you think you’d like to add more fiber to your diet, there are a few things you can do to help prevent side effects. 

  1. Go Slow! Our bodies are amazing machines, but they can’t go from zero to one hundred without some bumps. Increase your fiber intake gradually. Start by adding one fruit or vegetable each day and build from there. If you’re using supplemental fiber, begin with a quarter of the suggested dose and increase the amount over a week.
  2. Drink Up! For every few grams of fiber that you’re adding, make sure to increase the amount of water or other fluids you're drinking. This can help to ensure that your stool will remain moist and that you won’t become dehydrated. 
  3. Chew, chew, chew! Chewing your food well will help to mechanically break down the fiber into smaller pieces, making it easier to move it way through the digestive tract.
  4. Remember, some side effects are to be expected and are totally normal. If you eat a large volume of fibrous foods or any type of food for that matter, some bloating is to be expected as the stomach has to stretch to accommodate it. Flatulence, or tooting, is also to be expected. It’s completely normal to pass gas about 10-12 times per day.

If you’ve increased your fiber intake and you’re experiencing negative side effects (even after you’ve tried the above suggestions), reach out. We can take a look at the type and amount of fiber that you’re currently eating and can make recommendations to help you with your belly issues or any side effects that you may be experiencing. 

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