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Can You Eat Too Much Fiber? The Good and Bad

Written by Dr. Michael Ruscio, DC on September 6, 2025

Written by Dr. Michael Ruscio, DC on September 6, 2025 — Reviewed by Hilary Watts

• Fiber’s Pros and Cons|
• Signs You’re Eating Too Much Fiber|
• Fiber Types & Sources|
• Approaching Fiber with SIBO or IBS|
• How to Increase Your Fiber Tolerance|

Health influencers often tout fiber as a cure-all for digestive issues, weight-related problems, and challenges with overall well-being. But the truth is more nuanced. For some, fiber is a game-changer. For others—especially with irritable bowel syndrome (IBS), small intestinal bacterial overgrowth (SIBO), or chronic bloating—it can make symptoms worse.

The upside? With the right approach, most people can retrain their gut to handle more fiber over time. In this article, I will discuss when fiber is helpful, when it is harmful, and how to safely increase your tolerance.

When Fiber Is Good and When It Isn’t

If you have a healthy gut, fiber is great. It helps push waste through the digestive system and helps support your gut’s microbiome.

But there are certain situations when fiber can make gut problems worse. Here is a quick overview of the top three that I see in the clinic. 

• SIBO—When bacteria overgrow in the small intestine, even small amounts of certain fibers may lead to things like bloating, distension (when your stomach gets visibly bigger), diarrhea, and constipation. 
• Poor gut motility—When the gut isn’t moving properly, fiber can become trapped in the intestines for too long and may ferment, causing symptoms like gas and bloating. This can lead to constipation and reabsorption of the toxins and water that remain in the colon, making it even harder to have a bowel movement. 
• Inflammatory Bowel Disease (IBD) and gut inflammation—Fiber can also be irritating to the gut lining for individuals with an inflamed colon, such as those with IBD (Crohn’s disease and ulcerative colitis). 

Signs You May Be Eating Too Much Fiber 

Here are some telltale signs we see in the clinic with our clients who struggle with too much fiber:

• Gas, bloating, stomach pain, cramping, heartburn, or nausea after eating high-fiber foods
• Constipation (fewer than one bowel movement per day)
• Feeling heavy or uncomfortably full in the belly after or between meals
• IBS or IBD symptoms that flare when fiber intake goes up

These signs may indicate that improving your gut health is necessary before adding more fiber to your daily diet. 

In addition to what we observe in our clients, research confirms that excessive fiber intake may become problematic for some individuals 1 2. 

• Two studies found that switching from a typical low-fiber American diet to a high-fiber diet significantly increased bloating in people with high blood pressure 3 4.

• A high-fiber diet may worsen constipation and IBS symptoms. And a low fiber diet may be beneficial for certain gut conditions, like diverticulitis, IBD, and gut infections 2. 

• Fiber can worsen gas, bloating, and other gut symptoms in people with a low fiber tolerance 5. 

Fiber Types and Sources

Before we dive into which foods contain fiber, it helps to understand the basics. There are two main types of fiber—soluble and insoluble—and how your gut responds often depends on the balance between them. Fiber is found in all plant foods, and many of the following foods are considered high-fiber foods. 

Soluble Fiber

Soluble fiber dissolves in water, forming a gel that slows digestion. It helps lower cholesterol, regulate blood sugar, support the gut microbiome, and promote feelings of fullness 6. 

Common sources include: Oats, beans, apples, bananas, and psyllium.

Insoluble Fiber

Insoluble fiber doesn’t dissolve in water and adds bulk to stool. It can help digestion and prevent constipation. It supports intestinal health, may reduce the risk of diverticulitis and colon cancer, and helps food move more quickly through the digestive system 7. 

Common sources include: Whole wheat, nuts, beans, cauliflower, and potatoes.

Can fiber help IBS symptoms? 

A meta-analysis (study of studies) wanted to see if fiber helped improve IBS symptoms. The results showed that soluble fiber significantly improved IBS symptoms, but insoluble fiber (in this study, bran was used) did not 8.

However, most foods contain some combination of both soluble and insoluble fiber. 

In addition to soluble and insoluble fiber, we can also categorize fiber by how fermentable it is. Highly fermentable fiber may be more likely to trigger gas and bloating if you have a sensitive gut or are working to heal dysbiosis—gut bacteria imbalance. 

Fiber-Rich Foods

Soluble Fiber Sources

Examples of foods packed with soluble fiber include 9:

• Legumes
• Nuts
• Seeds
• Wheat
• Rye bread
• Onions
• Garlic 
• Artichoke
• Kashi
• Millet
• Oats
• Whole-grain pasta
• Potatoes
• Rice

Insoluble Fiber Sources

Foods rich in insoluble fiber include 9: 

• Wheat bran
• Whole-grain cereal
• Rye bread
• Brown rice
• Whole-grain pasta
• Potatoes
• Turnips
• Peas
• Okra
• Raspberries
• Apple with skin
• Pear with skin
• Green beans
• Kiwi
• Quinoa
• Flaxseed and other seeds
• Nuts 

Most foods, especially whole-grain pasta, nuts, seeds, and many fruits and vegetables, overlap in both categories. 

If you have trouble with large amounts of fiber, focus on small amounts of the foods from the soluble category first. Soluble fiber is more likely to improve IBS symptoms 8 and offers additional gut-health benefits, such as boosting butyrate levels. 

Can You Eat Too Much Fiber? How to Approach It With SIBO or IBS

If you have SIBO or IBS, it’s ok to eat fiber-rich food, but some types of fiber may be easier to digest than others. 

When you’re first starting a diet for SIBO or IBS, you may want to temporarily restrict most fiber—especially fermentable fibers—while your microbiome adjusts 10 11.

Many of our clients find that a low FODMAP diet works well for this adjustment period—more on this below. Once your symptoms have calmed down—and you’ve possibly added in probiotics and antimicrobials—then you can slowly begin trying more fiber-rich foods. 

Oftentimes, it is helpful to have a medical provider guide you through this process. Please reach out to our clinic if you are looking for personalized care. 

Low FODMAP Diet

A low FODMAP diet is a temporary eating plan that restricts certain fermentable fibers that may contribute to gas and bloating for people with IBS and SIBO. 

One study found that three weeks of a low FODMAP diet was linked to a significant (27%) improvement in IBS symptom scores compared to a high FODMAP diet, which came with a 7% increase in symptoms 12.

Another study found that just one week of a low FODMAP diet helped IBS patients have 13: 

• Fewer episodes of abdominal pain
• Reduced intensity of abdominal pain
• Improved bowel habits (firmer stools and less frequent bowel movements)
• Improved wellbeing

In contrast, all symptoms were worse for IBS patients eating a moderate FODMAP diet. The researchers also found that those who had more severe IBS symptoms saw the greatest improvements 13. 

Download: The Low FODMAP Guide

Psyllium

Psyllium fiber can be beneficial for people with sensitive intestines. It’s a soluble fiber, forms a gel, and is poorly fermented, which means it produces less gas and can be soothing to the digestive tract due to its gel-like consistency 14. Many popular fiber supplements, like Metamucil, contain psyllium powder in their formulations. 

Psyllium can be an excellent option for those who need to increase their fiber intake to relieve constipation or diarrhea, but who cannot tolerate the fermentable fibers in foods like beans, lentils, and whole grains.

Psyllium also serves as a low-grade binder, so it’s important to take it separately from medications and supplements 15. Be sure to consult your doctor before adding new supplements, such as psyllium, to your routine. 

In a recent science review on the role of fiber in gut health and disease, psyllium was the only fiber recommended for constipation-predominant IBS, diarrhea-predominant IBS, and functional constipation—but not for IBD and diverticulitis 16. 

If you want to try psyllium, you can get it in capsules or powder form. For powder, we have our clients start with as little as half a teaspoon mixed in 8 ounces of water. It’s easiest to add the psyllium powder and water to a jar and shake it to mix well. Drink immediately. If you find a benefit from taking it, you can increase your psyllium dose over several weeks to 15 grams (approximately 3 teaspoons) one to three times per day 16.

Resistant Starches

If you have a well-functioning gut, resistant starches are another type of fiber you may want to prioritize in your diet, because they can help boost good gut bacteria and lower gut inflammation 17. As a bonus, when your gut bacteria break down resistant starch, they produce beneficial short-chain fatty acids (SCFAs) 18.

One of these SCFAs is butyrate, the energy source for colonocytes (the cells lining the colon). Butyrate also has benefits for brain health and lowering body-wide inflammation 19.

However, resistant starches are easily fermented, so they may cause digestive problems in those with gut issues. 

Examples of resistant starches include 20: 

• Cooked and cooled rice and potatoes (cooking, then cooling for 12–24 hours helps increase resistant starch)
• Plantains and bananas
• Whole grains
• Beans and lentils

Helping the microbiome make SCFAs is one reason fiber may have body-wide health benefits, including a lower risk of stroke, digestive problems, weight-related health problems, and depression 19 21.

How to Increase Your Fiber Tolerance

It’s best to increase fiber intake slowly over time, and you may find your tolerance is lower during periods of stress or illness. Everyone’s capacity to handle fiber is different and may even be influenced by things like your sex at birth, ethnicity, unique microbiome, and previous eating habits 3 4. 

• In general, the recommended dietary intake in grams of fiber per day is 9:

You may need more or less depending on your gut health and what makes you feel good. 

If you’re starting to increase your fiber tolerance from a low FODMAP diet, reintroduce only one food at a time and see how you respond. If your symptoms return, go back to low FODMAP for a day or two and reintroduce a different higher-fiber food. The idea is that you’re giving your gut and your microbiome time to adjust and break down the new food before adding another. 

You can also experiment with different methods of cooking to make certain fibers easier to digest. For example, soak beans and legumes in water overnight and cook on the stove for 2–3 hours to break down the starch. This method will also eliminate lectins—compounds found in beans, grains, and other plant foods. 

Motility Is Essential to Handling More Fiber

Before increasing your fiber intake, it’s important to make sure your gut motility—the movement of food through your digestive system—is working well. Without good motility, fiber can backfire, leading to constipation and bloating (a common issue in SIBO).

Here are some key ways to support gut motility:

• ​​Improve vagal tone. The vagus nerve helps regulate digestive movement, but low vagal tone (seen in IBS, SIBO, and functional constipation) can slow motility 22. In the clinic, we use Auricular Vagus Nerve Stimulation (aVNS)—an effective method that delivers mild electrical pulses through the ear to activate the vagus nerve. You can also reset the vagus nerve with strategies like deep breathing, singing, and meditation 23. 
• Stay hydrated. Drinking enough water can help stool move more easily through the intestines. Mineral water may be especially helpful for improving gut motility 24.
• Move your body. Walking, yoga, and other forms of physical activity can help get things moving 25. I typically recommend at least 20–30 minutes of walking daily. 
• Set clear mealtimes and avoid grazing. Snacking frequently between meals may interrupt your gut’s migrating motor complex—the natural housekeeping system that clears the intestines 26. 
• Incorporate probiotics. Research shows probiotics can improve gut motility and support regular bowel function 27.
• Use gentle supports when needed. Magnesium citrate or glycinate, ginger, and senna can help promote healthy motility.
• Manage stress. Stress impacts the gut 28. Deep breathing, meditation, or relaxation practices may reduce the gut-brain tension that can slow down motility 29.  

Heal Your Gut to Handle More Fiber

To tolerate a higher amount of fiber in your diet, good gut health is essential. Your microbiome ferments certain kinds of fiber, producing gas alongside beneficial compounds like SCFAs. If you have a condition like IBS or SIBO, too much fiber may worsen your symptoms. 

However, fiber is an undeniable tool for health when used correctly and has implications for managing heart disease, weight-related health problems, and blood sugar levels. To improve your digestive system’s ability to handle fiber, make sure to: 

1. Go low and slow; start with a very small amount and increase over several weeks.
2. Make sure you’re drinking plenty of water alongside the added fiber in your diet.
3. Get your gut moving (good motility).
4. If you encounter digestive problems after eating certain fiber-rich foods, back off and reintroduce them later when your gut is more resilient. 

You can learn more about fiber and its potential effects on gut health in my book, Healthy Gut, Healthy You. For more personalized guidance, reach out to our functional medicine clinic.

The Ruscio Institute has developed a range of high-quality formulations to help our clients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you. The information on DrRuscio.com is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.