What is dietary fiber?

  • Fiber is a complex carb from plants that doesn’t get broken down into sugar. Starch is another complex carb that does get broken down to sugar
  • It generally contributes 0 calories to your diet
  • Some types of fiber, called prebiotic fiber, can help promote the growth of beneficial bacteria in your gut. Inulin, from chicory root, is an example of prebiotic fiber.

Why should you care?

  • Low (or no) Calories
  • Microbes eat fiber and make mucin, strengthening your gut barrier and preventing foreign molecules from leaking out of your gut into your bloodstream.
  • Fiber is bulky and it absorbs water, leaving you feeling full for longer. There is also evidence that high fiber foods will alter hunger hormones, making you crave food less.
  • Fermentation of some fiber leads to Short Chain Fatty Acid production (SCFAs)
  • Many SCFAs are anti-inflammatory and good for your immune system
  • The American Heart Association recommends between 25-30 grams per day from food.

Top 5 high fiber foods to achieve 25-30 grams per day

 Food % Daily value of fiber per serving
Lentils 56%
Black Beans 54%
Chickpeas 45%
Avocados 36%
Chia seeds 36%


Here's the full list

More details

The definition of dietary fiber is contentious and evolving. Let’s start with the broadest definition from the American Association of Cereal Chemists. Fiber is the:

“edible parts of plants or analogous carbohydrates that resist digestion and absorption in the small intestine, with complete or partial fermentation in the large intestine”

A mouthful, but all of that is important. Let’s dig in.

1) Yes, fiber is in the ‘carb’ family, but it’s more complex than that, pun intended. This is where the resistance to digestion comes in. Sucrose is a carb, but it is digested quickly into glucose and fructose, directly entering your bloodstream through the small intestine and either used for energy, or stored as fat.

Fiber refers to carbs that are not digested. In fact, they go all the way to your large intestine, your gut, where some get broken down by the bacteria that live there This also means that dietary fiber, while sometimes tasting quite sweet, generally does not contribute to increasing your blood sugar, and most of the time, does not contribute to calories in your diet.

Some types of dietary fiber, like Inulin, can promote the health of beneficial bacteria in your guy, and go by the name Prebiotics. Not to be confused with 'probiotics' which is the term for the bacteria themselves.

So, by eating fiber, you are directly feeding and growing a population of beneficial microbes that live inside of you. Conversely, if you’re not eating fiber, you’re not feeding your bug buddies, which can lead to “good” bacteria dying off. 

The final important piece of the definition is ‘fermentation’. Many things are fermented, think beer, wine, kombucha, or kimchi. This is the term for breaking down carbohydrates without the presence of oxygen, also is called anaerobic digestion. The products of fermentation can reduce inflammation throughout the body, a process covered in our post on diet and the immune system.

If you're interested in eating more fiber, check out our free fiber food guide.


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