Back to Basics: Dietary Fiber

This post is part of a blog series called “Back to Basics.” This series aims to combat the confusion exacerbated by flashy headlines and social media over what constitutes a nutritious diet by providing simple, sound nutritional science. It emphasizes that the concepts of a nutritious diet haven’t changed dramatically over the years but have simply been fine-tuned.


back to basics fiber

Fiber. You probably know that it makes you poop. You may have an idea of foods that are high in fiber. You read somewhere online that eating fiber helps you lose weight.

So — why is fiber important? Why does fiber make you poop? Can fiber help you lose weight? Read on to find out.

What is fiber?

According to the FDA, fiber is “non-digestible soluble and insoluble carbohydrates (with three or more monomeric units) and lignin that are intrinsic and intact in plants.”

In a nutshell — fiber is a component of plant foods (grains, nuts, seeds, fruits, and vegetables) that humans cannot digest. Thus, fiber moves through your digestive tract without being absorbed into your blood stream.

Why is fiber important?

You may be thinking, “If I don’t absorb fiber, my body isn’t using it, so why is it important?” Think again. Just as every player on a sports team has an important role no matter how often they are on the field, fiber has many important health benefits despite not being absorbed and used by your body in the same way as nutrients such as carbs or protein.

Overall, fiber helps keep you pooping regularly, makes you feel full longer, can help you have steadier energy levels, and is good for your heart health. The health benefits depend on the type of fiber.

Types of Dietary Fiber

There are two main types of dietary fiber that play important roles in your body. Soluble fiber is touted for its heart health and blood sugar regulating benefits, while insoluble fiber helps keep you regular.

Soluble Fiber (The one that is good for your heart)

You know how Cheerios commercials are always talking about how Cheerios can help lower your cholesterol? That’s because they contain soluble fiber. Soluble fiber is also the reason fiber helps you feel full and regulates your blood sugar levels.

As the term “soluble” implies, this kind of fiber absorbs liquid in the gastrointestinal tract and swells, forming a gel.

When you eat foods high in soluble fiber, the soluble fiber basically forms a blob of gel. The blob of gel takes more time to empty from the stomach into the small intestine, which makes you feel full longer. This decreases the probability of overeating or grazing later in the day, which is why people say eating more fiber helps you lose weight.

In addition to helping you feel full longer, the gel formed by the soluble fiber can help regulate your blood sugar. The gel formed by the soluble fiber traps the glucose (aka sugar) from the foods you eat, so the enzymes in your intestines that break down the glucose can’t reach the glucose as easily. Thus, it takes longer to digest the glucose and release it into your blood, which leads to a steadier rise in blood sugar. This slower rise in blood glucose isn’t as overwhelming to your body, and in turn, you have a more stable energy level throughout the day.

Along with promoting steadier blood glucose levels, soluble fiber can also lower cholesterol levels, which is good for your heart health. Just as soluble fiber traps glucose, it also traps bile acids. Bile acids are compounds that help your body absorb the fat you eat. They are made from cholesterol in your liver. When the bile acids are trapped by the soluble fiber, you poop them out, and then the liver has to use cholesterol to make more bile acids. Thus, there is less cholesterol in your liver, and your cholesterol levels decrease.

Insoluble Fiber (The one that makes you poop)

Insoluble fiber differs from soluble fiber in that it does not absorb water in the gastrointestinal tract. Basically, it helps move the foods through your digestive tract (aka — it helps you poop).

How Fiber Keeps your Colon Happy

Ever heard of this thing called the gut microbiome? Our intestines, especially our colon, contain a large number of beneficial bacteria. This healthy bacteria in your colon is called the gut microbiome. Research has found that the gut microbiome can play a role in obesity, diabetes, mental health, cancer, and a variety of other conditions; thus, we want to promote having more healthy bacteria in our colon. Fiber is one nutrient that can help with this.

While humans do not have the right enzymes to digest dietary fiber, the healthy bacteria in our gut does. The fiber feeds the gut bacteria, which helps increase the numbers of the good bacteria.

Additionally, when the bacteria in your large intestine eats the fiber, they produce compounds called short chain fatty acids, or SCFAs. SCFAs keep your large intestine healthy by:

  • Preventing the growth of harmful bacteria in your large intestine
  • Inhibiting tumor formation & abnormal cell growth (aka, preventing colon cancer)
  • Improving blood flow to your large intestine
  • Enhancing immune function (over 50% of the body’s lymphocytes and immune cells are found in the gastrointestinal tract!)

Keep an eye out for more research regarding the many positive benefits of a healthy gut microbiome! Meanwhile…eat some fiber. 🙂

How Much Fiber Should You have a Day?

Currently, Americans ages 2 and older only consume about 16 g of fiber per day, much lower than the current recommendation. The recommended amounts of fiber per day depend upon age and gender:

<50 years

  • Males: 38 g
  • Females: 25 g

≥50 years

  • Males: 30 g
  • Females: 21 g

Some people may require lower amounts of fiber due to a medical condition, such as during a flare-up of Chron’s disease, ulcerative cholitis, diverticulitis, or other gastrointestinal conditions. If you have one of these conditions, talk to your healthcare provider to understand if you need to alter your fiber intake.

Sources of Fiber

To keep it simple, if you want to increase your fiber intake, eat more plants! The foods that contain soluble vs. insoluble fiber vary a bit, but in general, you’ll be getting enough if your eating a variety of plant foods every day.

Sources of Soluble Fiber

  • Whole grains (especially oats & barley)
  • Fruits & vegetables (especially carrots, apples, bananas, strawberries, & citrus fruits)
  • Nuts & seeds

Sources of Insoluble Fiber

  • Seeds and skins of fruits
  • Whole grains
  • Leafy greens
  • Celery
  • Onions, leeks, scallions, garlic
  • Broccoli & cauliflower

The Takeaway

Even though fiber isn’t absorbed and used by your body in the same way as nutrients such as carbs and protein, fiber plays an important role in your health. Fiber helps regulate your digestion, improve heart health, and regulate blood sugar levels.

Try the following tips to increase the fiber in your diet:

  • Opt for whole grains (whole wheat bread, whole wheat pasta, brown rice, barley, oats, quinoa, etc.)
  • Eat at least five servings of fruits and vegetables per day. Try to have a fruit or a vegetable at each meal and snack.
  • Try adding some beans & legumes to your diet (perhaps even going meatless for a day). 
  • Use whole wheat flour instead of refined white flour in recipes.

Published by Talia Follador

Registered Dietitian Nutritionist (RDN) with a passion for holistic health, intuitive eating, psychology, and cooking. Proud Penn State alumnus, spiritual explorer, nutrition geek, baseball junkie. I like to have my cake and eat it, too . :)

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