Dietary Fiber Benefits, Myths and Food List

☑️ Evidence Based - Medical review by Po-Chang Hsu, M.D.

In this article, I tell you everything you need to know about dietary fiber, including its benefits, myths, and how much fiber you need per day. I also talk about the risk of ingesting too much fiber, give you a list of foods high in fiber, and much more.

So what is fiber? In a nutshell, fiber is not an essential nutrient because the body can’t absorb it and its absence does not cause any detectable state of deficiency. However, adequate daily fiber intake can reduce the risk of certain medical conditions. So continue reading to learn more.

How Fiber Works
How fiber works.

Increase Your Daily Fiber Intake!?

If you suffer from constipation, are pursuing weight loss goals, need to get your blood glucose (blood sugar) levels under control, or suffer from cardiovascular disease…

…the standard advice is to eat more fiber. So it seems like fiber is essential. But is fiber a nutrient or a vitamin? And what are the side effects of a low-fiber diet?

Fiber Definition What Is Fiber?

Fiber has a similar molecular structure as carbohydrates, but the human body lacks the necessary enzymes to digest it. As a result, fiber is not a nutrient.

Fiber is not an essential nutrient, but eating more of it has a number of important health benefits — and can even help prevent chronic diseases like cancer.

However, there are a number of known health benefits of fiber, and scientists regularly find more data to suggest that increasing your fiber intake is a good thing.

How Much Fiber Per Day Do I Need?

The Academy of Nutrition and Dietetics recommends 14 grams of total fiber per 1,000 kcal, or 25 grams for adult women and 38 grams for adult men. Scientists have based this recommendation on research that demonstrates the fact that fiber helps to lower the risks of certain diseases, including coronary heart disease.

However, if you were to adopt a zero fiber diet, you wouldn’t suffer from a deficiency or any immediate side effects — although you might increase your long-term risk of specific chronic diseases.

Can I Consume Too Much Fiber?

In general, if the fiber comes from natural sources like vegetables (as opposed to synthetic fiber supplements) the answer to that question is “no.” Our Paleolithic ancestors ate a significant amount of fiber — perhaps as much as 100 grams per day. While some recent studies have found that an extremely high-fiber diet may reduce the absorption of certain nutrients, the effect is insignificant. So there’s no need to worry about consuming too much (natural) fiber.

However, consuming a high-fiber diet may cause some uncomfortable ⁠— if relatively minor and overall harmless ⁠— gastrointestinal side effects in some people (which I describe in more detail later in this article). That’s because while it’s true that our ancestors consumed large amounts of fiber, their bodies were adapted to fiber in ways that our bodies tend not to be.

Paleolithic humans relied on hunting as a primary food source. But when they were unable to find animals to kill and eat, they had to turn to fiber-rich, plant-based foods that had relatively few calories. Modern humans don’t consume nearly as much fiber because we have ample supplies of high-calorie foods available in the supermarket. As a result, our guts aren’t used to high concentrations of fiber, and thus we experience symptoms when we try to eat “too much” of it.

Food with Insoluble and Soluble Fiber
Food with insoluble and soluble types of fiber.

Types of Fiber

Fiber is a collective name for a large number of molecules that are structurally similar to carbohydrates.

There are two categories of dietary fiber (soluble and insoluble), and there is also a synthetic version we can often find in supplements.

FiberCon - Synthetic Fiber
FiberCon: synthetic fiber, also known as calcium polycarbophil.

Synthetic Fiber

You can find synthetic fiber (calcium polycarbophil) in various supplements and processed foods. Manufacturers create synthetic fiber from non-digestible carbs that are similar to their natural counterparts. However, synthetic fiber might not be as effective and may cause more adverse side effects.

So, I recommend choosing natural sources of fiber for the same reasons as doctors recommend getting vitamins and minerals from food instead of from supplements: because there are a ton of micronutrients and chemicals in natural food sources that can influence how the body absorbs substances, which are often not present in synthetic sources.

Insoluble Fiber

Insoluble fiber does not dissolve in water, and thus it does not change to a gel-like structure. This type of fiber is typically responsible for increasing stool volume and improving bowel movements. So if you suffer from constipation, utilize fiber!

We can find it in most seeds, in whole-grain products (like whole-grain flour and whole-grain cereal), and in the skin of most fruits. Insoluble fiber does not have any effect on your blood sugar levels, but it can slow down the rate at which your body absorbs glucose. As a result, it lowers the glycemic index (GI) of food.

Soluble Fiber

Soluble fiber has a similar function as insoluble fiber, because it remains in your stool and improves gastrointestinal functions. However, it forms a gel after contact with water. As a result, this type of fiber binds with bile, a fluid that aids the digestive process and which holds a lot of cholesterol molecules. Thus, when your body excretes soluble fiber, all of the bile attached to it goes away, preventing cholesterol from returning to the bloodstream. That’s how soluble fiber can reduce cholesterol levels and improve cardiovascular health. Some foods with high soluble fiber content include nuts, apples, beans and oatmeal.

Note that it’s almost never a case of choosing between soluble vs insoluble fiber, as all fiber-rich foods contain both types of fiber to varying degrees. While the distinction between those two types is a bit out of date, manufacturers need to declare what kind of fiber they are offering in their products, especially if there are health claims on the package.

What Does Fiber Do to Your Body?

After making the distinction between the two natural types of dietary fiber, let’s take a look at what fiber does to your body.

Weight Loss

Both soluble and insoluble fiber can help if you’re trying to lose weight. One of the best ways to accomplish that is to reduce your carbohydrate intake and create a negative caloric balance. In other words, by eating fewer calories than your body burns.

Fiber is not absorbed or degraded, so it makes your stool bulkier and slows down your gastric emptying, thus making you feel satiated for a longer time. That helps to avoid those sugar cravings that would likely cause a rebound effect.

How fiber lowers blood cholesterol
How fiber lowers blood cholesterol.

Cardiovascular Improvements

For many years, fiber has been an ally if you suffer from cardiovascular disease (heart disease) or have an increased risk for the condition. Scientific studies and clinical trials determined that insoluble fiber coming from cereals and vegetables protects us from cardiovascular disease and coronary heart disease. On the other hand, fiber coming from fruits predominantly prevents cardiovascular disease.

Fiber reduces the glycemic index of foods, which keeps sugar levels and triglycerides under control. Plus, fiber helps improve cholesterol levels, as we discussed previously, by reducing specific types of it, such as LDL (low-density lipoprotein), and preventing atherosclerosis. There’s also evidence that dietary fiber lowers your blood pressure if you suffer from hypertension, especially when your systolic blood pressure is elevated.

Fiber can reduce insulin spikes
Fiber can reduce insulin spikes.

Control of Type 2 Diabetes

Increasing your fiber intake can help you as a preventative measure to reduce your risk of Type 2 diabetes. But it also helps diabetic patients control their disease. Fiber improves our insulin sensitivity, and increasing dietary fiber intake also slows down gastric emptying, improves digestive health, and slows down the absorption of glucose.

Thus, if accompanied by fiber, food has a lower glycemic index, which means that instead of experiencing violent spikes in your sugar levels, carbs will be absorbed at a steadier pace, allowing your body to keep sugar levels under control. Scientists still don’t fully understand the exact role fiber plays in reducing the risk of developing Type 2 diabetes. However, there is strong evidence of the benefits of fiber for those who suffer from insulin resistance or pre-diabetes.

Improvements in Bowel Movements

Both soluble and insoluble fiber can improve your digestive health. They create extra bulk in your stool, thus making it easier for your body to regulate bowel movements. Fiber also reduces the internal pressure in your gut. As a result, there’s a lower chance for you to develop hemorrhoids, polyps, and other intestinal problems. Both soluble and insoluble fiber are beneficial if you’re constipated, but if you’re experiencing diarrhea, doctors recommend soluble fiber.

Cancer Prevention

Research suggests that fiber is an effective means for preventing different types of cancer — especially colon cancer and breast cancer. According to the World Cancer Research Fund, there is convincing data that eating more fiber will reduce your risk of developing colorectal cancer. For every 10 grams of fiber we consume per day, the risk of cancer is reduced by an impressive 9%.

Researchers explain that fiber increases fecal bulk, which reduces the time of intestinal transit (i.e., the time it takes waste to move through the digestive tract). That, in turn, decreases the time your large and small intestine are exposed to particular carcinogens. On the other hand, fiber reduces the risk of breast cancer because it removes excess estrogen and modulates the activity of specific enzymes in the gut.

Fermentation of fiber in the colon
Fermentation of fiber in the colon.

Fermentation

As we will discuss further, our gut microbiota (good bacteria) is capable of degrading some types of fiber, especially β-glucans, oligosaccharides, and others. After fermenting fiber, your healthy gut bacteria start to produce short-chain fatty acids, a unique variety of fatty acids with a range of benefits.

Fiber and Prebiotics

Scientists have recently discovered that modulating the type of bacteria that colonize our intestines can have a positive effect on the rest of the body. That’s why there are so many studies about probiotics and prebiotics, and a slew of manufacturers offering unique probiotic strains directed towards a given ailment.

A prebiotic is a substance that selectively stimulates the growth of certain bacteria in the gut, and that’s precisely what inulin and fructo-oligosaccharides do. Their structure is similar to that of carbohydrates, but only certain (healthy) bacteria have the enzymes to degrade and use them. We can find these prebiotic fibers in garlic, onions, oats, leeks, peas, and other foods.

Given its properties, we can also consider fiber as a naturally-occurring prebiotic because even if our body can’t synthesize and absorb it, it’s a useful energy source for our healthy bacteria, and it promotes their growth.

But that’s not the end of the story. When bacteria break down fiber, they release short-chain fatty acids, as I mentioned earlier. Propionate, one of those fermentation metabolites, has implications for your health, reaching far beyond the gut. Specifically, those fatty acids can improve the normal function of the immune system, reduce cellular adhesion, and protect from inflammation.

Side-Effects of a High-Fiber Diet

As I mentioned previously, too much fiber does not cause significant health problems. However, in some cases, excessive fiber intake can cause specific symptoms and change the way our gastrointestinal system works.

It’s also worth noting that fiber is not a silver bullet or a solution to all of our gastrointestinal problems. There are inflammatory bowel diseases such as Crohn’s disease that will not benefit from fiber intake because the added bulk in the stool can cause intestinal blockages. Also, patients suffering from gastritis can aggravate their symptoms after eating fiber-rich foods because it slows down the gastric emptying.

Too much fiber can also cause intestinal gas and may increase the frequency of your stools. If you have a food intolerance, it may cause excessive bloating and flatulence. For instance, inulin can cause discomfort, abdominal pain, and bloating in sensitized patients. If you experience such conditions, I recommend that you stop consuming inulin-rich foods such as asparagus, leeks, and sugar beets. I realized a few months ago that I get incredibly bloated after eating asparagus and artichokes, and I think inulin is the reason.

Fiber Food List
Fiber foods list: click on image to see the full infographic.

High Fiber Foods List

Below are high fiber food charts, based on information from the Mayo Clinic. All amounts are in grams.

High Fiber Fruits

Fruits Serving Size Total Fiber
Raspberries 1 cup 8
Pear 1 medium 5.5
Apple Medium 4.5
Banana 1 medium 3
Orange 1 medium 3
Strawberries 1 cup 3

High Fiber Vegetables

Vegetables Serving Size Total Fiber
Green peas, boiled 1 cup 9
Broccoli, boiled 1 cup chopped 5
Turnip greens, boiled 1 cup 5
Brussels sprouts, boiled 1 cup 4
Potato, with skin, baked 1 medium 4
Sweet corn, boiled 1 cup 3.5
Cauliflower, raw 1 cup chopped 2
Carrot, raw 1 medium 1.5

High Fiber Legumes, Nuts and Seeds

Legumes, Nuts, and Seeds Serving Size Total Fiber
Split peas, boiled 1 cup 16
Lentils, boiled 1 cup 15.5
Black beans, boiled 1 cup 15
Baked beans, canned 1 cup 10
Chia seeds 1 ounce 10
Almonds 1 ounce (23 nuts) 3.5
Pistachios 1 ounce (49 nuts) 3
Sunflower kernels 1 ounce 3

High Fiber Grains

Grains Serving Size Total Fiber
Spaghetti, whole-wheat, cooked 1 cup 6
Barley, pearled, cooked 1 cup 6
Bran flakes 3/4 cup 5.5
Quinoa, cooked 1 cup 5
Oat bran muffin 1 medium 5
Oatmeal, instant, cooked 1 cup 5
Popcorn, air-popped 3 cups 3.5
Brown rice, cooked 1 cup 3.5
Bread, whole-wheat 1 slice 2
Bread, rye 1 slice 2

Tips to Increase Your Fiber Intake

According to studies, most Americans do not consume enough fiber in their diet. While increasing your fiber intake is relatively easy, there are some pitfalls you should try to avoid.

For example, one common piece of advice to increase your fiber intake is to eat whole grains and legumes (such as beans and lentils). While those foods are an abundant source of fiber, that fiber comes at a cost. Most types of grains (and especially wheat) contain gluten, while raw legumes are toxic — only cooking makes them edible.

Even after soaking and cooking legumes, they boast plenty of anti-nutrients, which is why I recommend staying away from them. So here are some better foods you can leverage as part of a high-fiber diet.

Breakfast Bowl with food high in fiber
Breakfast bowl with foods high in fiber.

Eat Nuts, Seeds and Fruits

Nuts and seeds are easy to carry around, and seasonal fruits are delicious snacks that can help increase your fiber intake.

Raspberries, for example, have a high fiber content (eight grams per cup) and they don’t have a lot of sugar — so you can even have them if you’re on the keto diet!

Unpeeled pears and apples are also good sources of fiber, but they contain more sugar than raspberries.

Avocados, another fruit, also contain a decent amount of fiber (10 grams per cup) and tons of healthy fats.

Do Not Peel Your Fruits

If you’re consuming fruits, remember that most of the fiber is located in the skin. In most cases, peeling fruits would only waste that valuable feature.

Avoid Juicing Fruits and Vegetables

While it’s true that natural juices are an excellent source of nutrients, they lack fiber. Without that fiber, your body gets hit with a ton of (fruit) sugar and your insulin levels spike. As a result, I recommend blending over juicing.

Eat More Broccoli

Broccoli is one of my favorite vegetables because it can modulate the gene expression in humans. Plus, one cup of it has about five grams of fiber.

Anthony's Psyllium Husk Powder
Anthony’s Psyllium Husk Powder.

Supplement with Psyllium Husk Power

If you’re struggling with maintaining decent fiber intake, you can also supplement with natural psyllium husk powder. I usually have two teaspoons of it mixed with water or as part of a protein shake after a workout. Psyllium husk is a natural product with three grams of water-soluble fiber per teaspoon. (Water-soluble means that it dissolves in water.)

Take Fiber Supplements

If psyllium husk powder is too messy for you, consider trying high-quality fiber supplements, such as the ones from Performance Lab. I recently tested their vitamin supplements and liked them.

Other Types of Fiber You Might Already Be Eating

Besides the most popular sources of fiber that I mentioned above, below are some more that you might already be eating without knowing it.

  • Guar gum: A natural substance that I have seen in all kinds of products, including meal replacement drinks.
  • Resistant starch: A type of carbohydrate (starch) you can find in numerous fruits and vegetables. In contrast to other types of starches, resistant starch doesn’t get digested in the small intestine, and thus it doesn’t raise your blood glucose level. However, the bacteria in the large intestine metabolize it through fermentation. As a result, you could also classify resistant starch as fermentable fiber.
  • Inulin and oligofructose: Oligofructose is a sub-group of inulin. You can find it in supplements, Jerusalem artichokes, bananas and onions, among other foods.

How Do You Know If You Should Eat More Fiber?

Look at your stool! According to the Bristol Stool Chart, your stool should look like Type 3 or 4 in the chart below.

Bristol Stool Chart
Bristol Stool Chart.

If it doesn’t, try eating a few spoons of psyllium husk powder and notice the difference the next day. Of course, there are numerous reasons why your stool looks like it does, and it’s not always a lack of fiber. But unless you have a medical condition, chances are that fiber (or lack thereof) may play an important part role.

Conclusion Do You Need Fiber in Your Diet?

Fiber is not an energy source for us, and we can’t consider it an essential nutrient to sustain life. However, there are some notable health benefits of fiber. Fiber feeds our healthy gut bacteria, improves our digestive process, and scientists have demonstrated the benefits of fiber on reducing certain chronic diseases (including cancer and heart disease). As a result, I consider fiber an excellent addition to an already healthy diet.

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