It’s easy to spot media stories telling us to eat more fiber for a healthier life and better gut health.
We can see them pretty much every day, whether online, on TV or in the newspapers.
Also, there are dozens of studies vouching for the digestive health benefits of dietary fiber.
However, consuming any nutrient in excess can be problematic, and fiber is no exception.
In fact, there are some little-known side effects that too much fiber can cause.
This article examines this issue and discusses seven potential risks from consuming excessive fiber.
Can You Have Too Much Fiber?
Just because fiber has benefits doesn’t mean we should eat as much of it as we can.
For one thing, it is possible to experience adverse effects if we consume too much, especially when supplementing.
Some possible symptoms of excessive fiber intake include stomach and digestive issues such as bloating, cramps, and gas.
But how much fiber is too much?
The “official” recommended daily fiber intake is set at 38g for men and 25g for women (1).
Anyone eating a standard whole-foods-based diet is unlikely to exceed this amount greatly.
However, those who go overboard on green smoothies, fiber supplements, and excessive amounts of grains might far exceed this figure.
More isn’t always better, and an excessive amount of fiber can cause problems.
There are also various factors which affect the digestibility of fiber.
For one thing, fiber can either be fermentable or non-fermentable.
Human digestive enzymes are unable to digest fiber, so it passes through the small intestine unchanged.
Instead, it is fermented and digested by the “good” gut bacteria (which make up the microbiome) in the colon and large intestine.
To put it differently, our body has no enzymes which can digest fiber, making us reliant on this gut bacteria.
Examples of fermentable fiber include most fruits and vegetables, and certain grains such as oats.
Non-fermentable fiber is resistant to bacterial fermentation in the colon and passes through the digestive system.
It is a bulking agent which thickens stools and “by mechanical stimulation/irritation of gut mucosa,” it decreases transit time (4).
We can find nonfermentable fiber predominantly in cellulose-rich foods, such as cereal (whole) grains.
This type of fiber slows the digestive process down and leads to our body digesting the food over a longer period.
However, some studies show that a higher intake of fiber can slow digestion too much and possibly cause constipation (7).
Overall, most studies on foods containing fiber do show benefit, but it’s worth being aware of possible problems from consuming too much.
Problems Caused by Too Much Fiber
Here are a few signs, symptoms and problems that excessive fiber intake can cause.
Usually thought of as a consequence of too little fiber, constipation may also result from an excessive intake. In fact, it can even be worse than on a low-fiber diet (8).
One study investigated fiber intake in 63 constipation patients who were currently on a high-fiber diet. The researchers split the participants into three groups; a no fiber, reduced fiber, and continuous high fiber diet plan.
Surprisingly, only the participants reducing their fiber intake saw a benefit. Participants who reduced their fiber intake had improvements in straining, gas, constipation, and anal bleeding (9).
An over-consumption of fiber may cause constipation through a build-up of undigested fiber in the digestive tract. The risk is higher when first increasing fiber in the diet, so it’s important to increase fiber slowly if you plan on making any significant dietary change.
2. Nutrient Malabsorption
In reality, most people already consume relatively low fiber diets. As a result, it’s rare to impede the absorption of nutrients through excessive fiber intake.
However, insoluble fiber—mainly found in whole grains—can reduce our absorption of certain nutrients.
For example, a recent randomized trial showed that a high intake of fiber causes a “slight but significant” reduction in calcium absorption (14).
Whole grain sources of fiber are also sources of antinutrients like phytic acid. While phytate can have some beneficial effects on our body, it’s also capable of binding minerals.
3. Gas and Bloating
Gas and feeling bloated are two of the most common complaints against a high fiber diet plan.
Since we think it’s the healthy thing to do, many people go overboard and include too much fiber-rich food in each meal.
As the microbiota in our gut digest fiber, the process produces various gases. This gas can lead to belching, flatulence and abdominal bloating, causing a considerable amount of discomfort to sufferers (17, 18, 19).
If this is something that sounds familiar, then consider how much fiber you’re consuming.
This digestive distress is especially common when increasing fiber intake suddenly (20).
Foods such as beans and cruciferous vegetables like cabbage, kale, and sprouts are common culprits for gas production.
4. Abdominal Cramping
Stomach cramps can be both painful and frustrating, and they can sometimes be a sign of excessive fiber intake.
In this case, it is a build-up of gases in the colon that causes the problem by exerting pressure on the colon walls.
A systematic review of randomized controlled trials demonstrates that fiber intake can relieve symptoms of irritable bowel syndrome – except for abdominal pain. This study found that “in some cases, insoluble fibers may worsen the outcome” (22).
While stomach cramping may be a sign of too much fiber, if it persists then seeing a doctor for an accurate diagnosis is important.
5. Intestinal Blockage
Fortunately, this condition is very rare and unlikely.
Notably, too much fiber can increase the risk of a phytobezoar developing. This condition is a large, trapped mass in the digestive system which consists of fruit and vegetable fibers.
Coupled with inadequate chewing, a large intake of high-fiber food is one of the biggest risk factors for a phytobezoar (25).
Dehydration as a result of excessive fiber depends on how much fluid the individual is consuming in the first place.
If it is an inadequate amount and fiber consumption increases, then it’s a possible cause of dehydration.
For larger amounts of dietary fiber, it’s important to ensure sufficient water intake.
You may have heard the “eight glasses per day” suggestion for water intake, but there isn’t much evidence behind this.
It’s incredibly difficult to ascertain how much water each individual needs, as this depends on so many different things. For example; the climate, physical activity, diet, and each person’s unique biology can all influence hydration levels.
With this in mind, judging water requirements by listening to thirst and urine color (ideally pale yellow) is ideal.
7. Acid Reflux and GERD
Recently, evidence suggests that small intestinal bacterial overgrowth (SIBO) may cause some cases of acid reflux.
Acid reflux is otherwise known as gastroesophageal reflux disease (GERD), but you may know this best as heartburn.
Heartburn is a digestive disorder in which stomach acid leaks into the esophagus, and it may cause anything from mild discomfort to sharp, burning pain.
In cases of heartburn, gas from the bacterial fermentation of carbohydrates can rise upward. As a result, these gases put pressure on the LES valve (lower esophageal sphincter) which keeps acid in the stomach and out of the esophagus.
For this reason, lowering carbohydrate levels has been put forward as a potential therapeutic solution to GERD.
There appears to be strong evidence too.
For instance, a recent 16-week study of 144 obese women with GERD saw all symptoms resolve in all women on a low-carb, high-fat diet (30).
How to Counteract Too Much Fiber
What can you do if you overeat fiber?
If you have symptoms of consuming too much, then the most important ways to counteract them are;
- STOP fiber intake until the condition subsides: consuming more fiber when there is a large amount still undigested will worsen the problem.
- Drink lots of water – adequate hydration will help with the digestion process.
- Do some light exercise such as walking: exercise and movement are known to help improve constipation and speed digestion up.
Like with many things in nutrition, there isn’t always a clear black and white.
Despite all the health claims we read about fiber, it’s important to be aware of the possibility of adverse effects at higher levels of consumption.
It’s also worth remembering that some fiber-containing foods are incredibly nutritious – avocados, raspberries, and cacao just to name a few.
Want to read more on the potential negatives of fiber?
Then the popular book ‘Fiber Menace’ might be worth a read.