Can You Eat Too Much Fiber in Your Diet?

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You may know that the 2015-2020 Dietary Guidelines for Americans recommend 25-35g fiber per day for individuals aged 14-50 and 21-30g for adults over 501.

Although average intakes in the US are lower than what is recommended2, those of us who are conscientious about what and how much we eat might be consuming more fiber than we realize.

If you are on a low-carb or low-calorie diet, or if you are not consuming a diet rich in high-fiber foods like beans, grains, fruit, and vegetables, it can certainly be difficult to meet daily fiber recommendations.

For the rest of us, it is perhaps easier than ever to reach our fiber goals, with an abundance of big-brand, high-fiber snacks at many grocery stores. Protein bars and packaged snacks often contain added fiber through ingredients such as chicory root fiber or soluble corn fiber, with some popular brand bars having about 15g of fiber per bar.

While many Americans struggle to reach the recommended daily fiber goals, many others struggle to avoid consuming “too much” fiber.

But what really happens when we exceed 25-35g fiber per day? Is the excess fiber even better for us?

The Case for High-Fiber Diets​

Fiber, an indigestible type of carbohydrate, has short-term and long-term health benefits. A high-fiber diet has been associated with reduced cholesterol3 and blood pressure levels4 and may help to alleviate symptoms of inflammatory bowel disease5. High-fiber diets can also reduce the risk of several diseases, such as type 2 diabetes6, heart disease7, breast cancer8, and pancreatic cancer9.

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There are two main types of fiber, and both are necessary to achieve health benefits.

Soluble fiber slows gastric emptying, can help lower blood sugar levels and can help make you feel full, while insoluble fiber can help move food through your digestive system. Soluble fiber can be found in foods like oats, fruit, vegetables, and beans; insoluble fiber can be found in foods like intact whole grains, fruit skins, root vegetables, and leafy greens.

Side Effects of Too Much Fiber​

Clearly, evidence suggests that high-fiber diets are beneficial in the long run, but if you consume a diet rich in whole foods and/or high-fiber packaged snacks, you might experience negative side effects from your high fiber intake. Because fiber is not digested, it can be difficult for large amounts of fiber to move through the digestive system. If you are concerned that your fiber intake is too high, here are some signs to look for:

1. Feeling uncomfortably full: One of the most common signs that your fiber intake is too high is simply feeling too full, which can lead to decreased appetite and food intake. It’s not just that consuming a high-fiber meal can make you feel full when you’re done eating, but rather that excessively high fiber intake can make you painfully full for several hours after the meal is over. It can be difficult to eat at your next meal if you are still uncomfortably full from your last meal.

2. Bloating or gas: Large amounts of fiber in the GI tract can lead to bloating and gas. Fiber creates bulk, and bacteria in the colon can digest fiber and create gas as a result. Bloating and gas can also be accompanied by abdominal pain. The degree of pain can range from trivial to very severe depending on your situation.

3. Diarrhea or constipation: Consuming a high fiber diet without adequate fluid intake can lead to constipation, especially if much of the fiber is soluble fiber, e.g. from fruit or oatmeal. If constipation is not treated, an intestinal blockage can result; however, reducing fiber intake can help to alleviate constipation10. On the other hand, too much insoluble fiber, e.g. from leafy greens or wheat, can push the contents of the GI tract quickly and cause diarrhea.

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4. Poor nutrient absorption: Poor nutrient absorption is a less obvious side effect of consuming high fiber diets, but it is important nonetheless, as it can have negative long-term health consequences. Fiber can bind to and decrease the absorption of certain minerals, such as calcium, magnesium, iron, and zinc.

However, human and animal studies have failed to show this decreased absorption so far; decrease in mineral absorption may be offset by colonic fermentation of dietary fiber, which may liberate bound minerals and promote their absorption11. Nevertheless, it is a good idea to be mindful of overall nutrient intake if you consume a high-fiber diet.

How Much Fiber is Too Much?​

The Adequate Intake (AI) for fiber is 14g per 1,000 kcal per day. The protein bars we mentioned earlier with 15g fiber per bar typically only have 200-250 calories per serving! If you ate two high-fiber bars in one day, then you wouldn’t need any more fiber for the day, but you would still have several meals left for the day. If you also ate 2-3 meals rich in nutrient-dense, whole foods, you could end up consuming 2-3 times the recommended fiber intake.

The exact amount of fiber that is “too much” will vary for each person. Changing fiber intake from day to day is important. If you consistently consume 30g fiber but then consume 60g fiber in one day, you will likely notice negative side effects. On the other hand, someone else might be used to eating 60g fiber per day with no negative side effects.

Take note if you feel uncomfortably bloated, gassy, constipated, or full, as these may all be signs of unnecessarily high fiber intake.

Finding Your Fiber “Sweet Spot”​

If you aren’t already aware of your typical fiber intake, it can be a good idea to track your intake for a few days. Once you know your fiber intake, you can monitor any digestive symptoms and gauge whether any of the side effects mentioned earlier could be due to fluctuations in fiber intake.

If you do experience negative side effects from a high-fiber diet, here are some low-fiber foods to focus on: meat, dairy, cooked or canned fruit and vegetables, and refined grains.

However, it is estimated that only 5% of the population meets the recommendation for fiber (Dahl). If you struggle to get adequate fiber, here are foods to focus on: whole fruit and vegetables, whole grains, legumes, nuts, seeds, and fiber-fortified foods containing ingredients such as corn fiber and guar gum. Bars or other packaged snacks with a high fiber content typically have one or more of these added ingredients.

To reiterate, it’s fairly easy to meet fiber recommendations if you consume a diet rich in high-fiber foods. One cup of berries with breakfast, an ounce of almonds with a snack, a cup of pasta with lunch, and a potato and cup of broccoli with dinner will put you over 25g fiber for the day. A high-fiber protein bar and an ounce of chia seeds is another way to easily get 25g fiber for the day.

Although there are standard guidelines set, you may find that you feel best when you consume higher or lower levels of fiber as compared with what guidelines recommend. Although it is much more common to consume too little fiber than to consume too much, it is still possible to have a fiber intake that is too high.

Getting too much or too little fiber can result in painful short-term side effects and negative long-term consequences, so it’s important to stick with what works best for you and to consult with your doctor if you have any concerns about your fiber intake.