Nutrition Basics: Fiber (You Need More of this F-Word in Your Life.)


In my recent posts about constipation and diarrhea, I told you that one possible solution to both problems is more fiber. That may seem counter-intuitive that problems on the opposite ends of the same spectrum could have the same solution, but it’s true. And I promise you will be perfectly clear about how this works by the end of this post!

Our starting premise: fiber is seriously important to our health and most people don’t get enough of it. In fact consuming enough fiber is so important, it’s #3 on my things you can do to improve your nutrition right now and I have been known to tell clients, “If you change nothing else about how you eat and drink, get plenty of fiber and drink loads of water.”

So let’s jump in to the details so that you understand why this is so critical to your health and well-being…

What is fiber?

Before we get into the more interesting details about what fiber does for us, I want to be sure you understand what fiber is.

As a general statement, fiber is the group of substances in the diet that are not digestible by us because we lack the appropriate digestive enzymes. At this level, fiber is split into two categories:

  • Dietary fiber: edible, non-digestible carbohydrates and lignins that make-up the structure of plants, from seed to maturity (By the way, this is what is listed on the Nutrition Facts Label.)
  • Functional fiber: non-digestible carbohydrates which have been isolated or extracted from plants or manufactured in a lab and have been proven through research to be beneficial to humans. Functional fiber may be added to foods or beverages to increase their fiber content or sold as a dietary supplement.

(You may notice from these definitions that only “functional fiber” has to be defined as something that is good for humans, as we already know that consuming plants, which contain dietary fiber, is beneficial to our health.)

Regardless of where the fiber came from, the following are the properties that determine what happens in the body once the fiber is ingested:

  • Solubility: whether or not the fiber dissolves in hot water
  • Fermentability: whether or not the fiber can be “digested” by bacteria. If fiber is fermentable (i.e., digestible) by the good bacteria in our guts, it is called a prebiotic.
  • Viscosity: the water-holding capability of the fiber (i.e., to what extent does it bind with water). The more viscous a fiber is, the more it soaks up water and digestive juices as it moves through the digestive tract. Viscosity is determined by the:
    • Solubility of the fiber,
    • pH (i.e., acid level) of the gastrointestinal tract,
    • Size of the fiber particles, and
    • Amount of processing the fiber went through.
  • Adsorbability: whether or not the fiber binds or adheres (i.e., adsorbs) substances such as nutrients, enzymes and toxins in the intestine (Note: this is different than viscosity as it isn’t just about liquid, it’s about holding onto “stuff” that is made of molecules bigger than H2O.)

As you can see, there’s a lot of different characteristics to fiber and, as I’ll explain in a bit, each of these makes a difference in how the fiber benefits your body. To wrap up this section, here is a summary of the types of fiber and their properties:

Fiber Type Dietary / Functional Soluble Fermentable Viscous Adsorption
Cellulose Both No Poorly No ???*
Hemicellulose Dietary Both Both No  Some
Pectin Both Yes Yes Highly  Yes
(different from lignan)
Both No Poorly No  Yes
Gums Both Yes Yes Yes  Yes
(a type of hemicellulose, technically)
Both Yes Yes Highly Yes
(includes inulin, oligofructose and fructooligosaccharides [FOS])
Both Yes Yes No Some
(inulin for sure)
Glucomannan Both Yes Yes Highly Yes
Resistant starches
Type 1: Located within the cellulose wall
Type 2: Located in granules within plant cells
Type 3: “Retrograde starch”
Type 4: Chemically modified starch
1, 2, 3 = Dietary
4 = Functional
No 1, 2 = Yes
3, 4 = Partially
No ???*
Chitin and chitosan Functional Some chitosans only Poorly Yes  Some chitosans only
Polydextrose and polyols Functional Yes Partially Yes  Some
Psyllium Functional Yes Yes Yes Yes
Resistant dextrins Functional Yes Yes No  ???*

* I couldn’t find adequate information to determine if these types of fibers adsorb or not.

What does fiber do in the body?

Even though we consume it, the purpose of fiber is not to nourish us. Well, not directly, anyway.

As it works it’s way through the digestive tract, these are all the ways fiber benefits our health based on its characteristics:

  • Soluble fiber:
    • Delays gastric emptying, so we feel full longer and consume less calories over time (this is one of the reasons why people who consume more fiber tend to be thinner)
    • Increases transit time (i.e., slows how quickly food moves through the intestines), which is good if you struggle with diarrhea
    • Decreases nutrient absorption (such as glucose, which is great for avoiding a blood sugar spike)
  • Insoluble fiber:
    • Speeds up intestinal transit time, which is good if you have constipation
    • Increases stool bulk (important so the muscles of the intestine wall have something to push on)
  • Fermentable fiber feeds the good gut bugs living in our large intestine and:
    • Encourages the growth and reproduction of good gut bugs, which helps keep bad gut bugs in check
    • Produces short chain fatty acids (SCFAs), which:
      • Increase absorption of sodium and water in the colon
      • Provide energy to the cells of the colon
      • Improve blood flow to the colon (which can help with constipation)
      • Encourage growth of new cells in the colon
      • Inhibit formation of tumors (i.e., reduces the risk of colon cancer)
      • Boost immune system function
    • Generates vitamins, including K, B12, biotin, folate and thiamine, which can be absorbed into the blood stream

Note: You can eat or take all the probiotics that you want, but if you aren’t feeding the good gut bugs, they will die. And if they’re dead, they can’t give you all the benefits above!

  • Viscous fiber:
    • Increases the volume of the stool so you have a solid-ish mass to push out (much more satisfying than thin or watery feces)
    • Decreases the transit time, again which is good if you have constipation
    • Reduces the nutrients available for absorption in the blood stream (i.e., fewer “calories in”) by interfering with the contact between digestive enzymes and food, so the enzymes can’t get to the food to digest it
    • Slows the rate at which nutrients are absorbed, which helps prevent a blood sugar spike and, therefore, maintain a more even blood sugar level over time
  • Adsorbing fiber binds to substances so that they cannot be absorbed, such as:
    • Bile salts (Normally, the body recirculates bile salts by excreting them into the intestine to help with fat digestion and then reabsorbing them for later use. By preventing their resorption, the body must make more, and the building block for bile is cholesterol. If you’ve ever wondered how Cheerios help lower blood cholesterol, this is it! Cheerios are made from oats which are rich in beta-glucans and are highly adsorbable. So the beta-glucans bind to the bile in the intestine and then the body must make more bile using some of the cholesterol from the blood, which reduces the amount of cholesterol left in the blood. So, ridiculously cool, isn’t it?!)
    • Toxins which may be in the food we eat, released by microorganisms living in the gastrointestinal tract, or bound to bile that is excreted into the intestine
    • Fats (obviously, we need fat, but maybe not as much as we eat sometimes 🙂 )
    • Calcium, magnesium, zinc, iron, carotenoids and some phytonutrients (IMPORTANT NOTE: It is obviously not a good thing for these nutrients to be bound up by fiber, if that means they are not available for absorption and use by us. However, there is some evidence that fermentation releases at least some of these nutrients from the hold of the fiber and then they can be absorbed in the colon. That being said, at least some stay bound up, so it’s important to not take a fiber supplement at the same time as other supplements or medications.)
    • Nitrogenous waste (such as from protein digestion) and carcinogens (again may be related to fibers impact on colon cancer)
    • Estradiol and Sex Hormone Binding Globulin (SHBG), which could help with estrogen dominance and may be why increased fiber intake is related to lower breast cancer risk

That is a LOT of goodness coming from one group of substances! And the best part is that every type of fiber has various properties so you get several good effects from each fibrous food that you eat. Fabulous!

How much fiber do I need?

According to the National Academies of Science, the following are the minimum amounts of fiber that we need in our diets each day based on age:

Age Females Males
< 1 year N/A N/A
1 – 3 yrs 19 g 19 g
4 – 8 yrs 25 g 25 g
9 – 13 yrs 26 g 31 g
14 – 18 yrs 26 g 38 g
19 – 50 yrs 25 g 38 g
51+ yrs 21 g 30 g
Pregnancy 28 g N/A
Lactation 29 g N/A

It’s important to note that this is the Adequate Intake (AI), which means that you may require more or less based on your physiology, biochemistry, current state of health, etc. However, without a specific reason, I strongly suggest you get at least the above amounts, primarily from food or supplements made from food (more on this in the next sections).

What foods contain fiber?

All plant foods contain fiber, as fiber is carbohydrates in a format that creates structure and form. So, as a general rule, if you are getting lots of vegetables and fruits (especially with the skin on, where appropriate), legumes, nuts, seeds, and whole grains (the more “whole” the better), then you will be getting plenty of fiber. In fact, this is one of the reasons that a plant-centric diet is so beneficial to our health!

More specifically, the following are foods that contain the different types of dietary fiber (since you should try to get most, if not all, of your fiber from food):

  • Cellulose: bran, legumes, nuts, seeds, peas, root vegetables, cruciferous vegetables (including cabbage, brussels sprouts, cauliflower and broccoli), and apples
  • Hemicellulose: bran (including from wheat, barley, rice, corn and oats), nuts, legumes, skin of some fruits and vegetables (including beets, potatoes and tomatoes… which is why I always eat the skin of my baked potato and leave the skins on when I make mashed potatoes)
  • Pectin: pretty much all fruit, but especially apples, apricots, cherries, quince, plums, gooseberries, oranges and other citrus fruits; some vegetables (like carrots, beets and cabbage) and legumes
  • Lignin: the stems and seeds of most fruits and vegetables, especially wheat, mature root vegetables, flaxseed, fruits with edible seeds (like raspberries), and bran
  • Gums: found naturally in oats, barley and legumes, but often extracted from plants and used as a thickener in various foods (you’ll recognize it on the label as gum arabic, gellan gum and guar gum). Note: studies have shown eating a large amount of gums, which is really only possible when consuming it as a food additive, causes digestive upset for some people.
  • Beta-glucans: oats and barley (primarily), rye, wheat, baker’s yeast and some mushrooms
  • Fructans: wheat, rye, barley, onions, leeks, garlic, Jerusalem artichokes, asparagus, corn, beets, brussels sprouts, broccoli, savoy cabbage, radicchio, fennel, chicory, peas, cashews, pistachios, nectarines, peaches and watermelon
  • Glucomannan: elephant yam (aka, konjac), which is used to make shirataki noodles and konjac gel, is the only food source that I could find and seems to be the beginning material of glucomannan supplements
  • Resistant Starch (types 1, 2 and 3): whole grains, legumes, seeds, unripe bananas, plantains, raw potatoes, cooked and cooled starches (including rice, pasta, corn and potatoes)

I know that’s a lot of information to take in and you could spend hours trying to figure out how to get each specific kind into your diet. But as I said above, if you are eating a variety and plenty of vegetables, fruits, nuts, seeds, legumes and whole grains, as is appropriate for your health goals), you will get all the different kinds of fiber!

Now, I will put one caveat on the above… eating a lot (or any) grains may not be appropriate for your health goals.  As well, if you are sensitive to gluten, you want to avoid wheat, rye, barley and any products made from them. Staying away from these won’t prevent you from getting the fiber you need, as there are plenty of other whole foods that have lots of fiber as you can see above.

What about fiber supplements?

You know I’d be doing you a disservice to talk about fiber supplements without first saying that you should try to get all the fiber you need from real food. Now, with that being said, you may find it difficult to meet your daily fiber needs without a fiber supplement and/or you might just feel better using one. To get really personal for a minute, I use a fiber supplement pretty much every day as I seem to poop better when I have it, than when I don’t, regardless of how many plant foods I eat in a day.

If you want or need to use a fiber supplement, pick one that is as natural as possible. This means staying away from most of the functional fibers and many of the commercial supplements, as they are way over-processed.

Also, be sure to buy one that has both soluble and insoluble fiber, which will be denoted on the Nutrition Facts Label. Although solubility isn’t the most important property of fiber, it does tend to correspond to the fiber’s fermentability, which is important for gut health.

Here are the fiber supplements that I recommend:

  • Garden of Life Super Seed (this is my go to and has been for ~15 years, although Garden Life has other fiber supplements that are likely as good)
  • Thorne FiberMend
  • Klaire Labs Biotagen (capsule form, in case taking a powder version doesn’t work for you)
  • Psyllium seed husk powder or flakes
  • Ground flaxseeds (because flaxseeds are also high in fat, which can go rancid, I recommend buying whole flaxseeds, keeping them in the refrigerator and grinding a small amount at a time for use)

As mentioned above, because many fibers have adsorbing capability, they can bind up useful substances such as vitamins, minerals and medications. As such, do not take other supplements or medications within 30 minutes of taking a fiber supplement.

Note: If you would like to support my business and order any of the above supplements from me, follow these instructions: Nutrition QED – Supplement Ordering Instructions – NP Script. As with all supplements, be sure to consult with your healthcare provider before taking them.

How do FODMAPs fit into this equation?

FODMAPs are fermentable oligo-, di-, monosaccharides and polyols. Basically, it’s all fermentable carbohydrates including those listed above and lactose. They have been grouped together based on research which shows that some people’s digestive issues are caused by these carbohydrates. In fact, research from Monash University in Australia has revealed that some people who thought they were gluten sensitive actually have trouble with FODMAPs, since wheat, rye and barley are high in gluten (a protein) and these particular carbohydrates.

Some healthcare providers suggest that anyone with Irritable Bowel Syndrome (IBS) should try a low FODMAP diet. My problem with this approach is that a low FODMAP diet is quite restrictive and difficult to follow. As such, I recommend people remove as few foods as possible to find relief, while also resolving any underlying causes of digestive upset (like small intestine bacteria overgrowth [SIBO]). This means some people may have to follow a low FODMAP diet in order to find complete digestive relief… and in that situation, the restrictions may be worth it!

What else do I need to know about fiber?

When increasing your fiber intake, go slowly! Even if you don’t have dysbiosis or other digestive issues, quickly increasing your fiber intake can cause them. Your body should get used to the increased amount of fiber within a relatively short period of time and then you can bump up your intake a bit more, continuing in this step-wise fashion until you have reached the target amount for your age. If you continue to have digestive trouble, seek the help of a healthcare provider (like me!) to help you figure out what’s going on.

As you increase your fiber intake, be sure to increase your fluid intake at the same time. Otherwise, the fiber won’t have enough water to remain soft and pliable and this can lead to constipation.

Bottom line: Adequate fiber intake is crucial for gut health and overall well-being, based on the benefits imparted to us by the various properties including solubility, fermentability, viscosity and adsorbability. Get enough of each type by eating a variety of veggies, fruits, legumes, nuts, seeds and whole grains (as appropriate).


Image courtesy of Life of Pix.

— Conlon MA, Bird AR. The impact of diet and lifestyle on gut microbiota and human health. Nutrients. 2014;7(1):17-44.
— Gibson P. Beating the bloat: the FODMAP diet and Irritable Bowel Syndrome. [Video] October 30, 2013. Accessed March 28, 2016.
— Goldin BR, Woods MN, Spiegelman DL, et al. The effect of dietary fat and fiber on serum estrogen concentrations in premenopausal women under controlled dietary conditions. CANCER-PHILADELPHIA. 1994;74:1125.
— Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth Cengage Learning; 2013.
— Kresser C. Harmful or Harmless: Guar Gum, Locust Bean Gum, and More. December 13, 2013. Accessed on March 28, 2016.
— Linus Pauling Institute. Fiber. Reviewed April 2012. Accessed on March 28, 2016.
— National Academies of Science. Dietary Reference Intakes: Macronutrients. Accessed on March 28, 2016.
— The George Mateljan Foundation. Fiber. In The World’s Healthiest Foods. Accessed on March 25, 2016.

Previous Post Next Post

One Comment

Comments are disabled