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Dietary Fiber: A Detailed Beginner’s Guide

Written by Lauren Panoff, MPH, RD

Reviewed by Anthony Dugarte, MD 

Published on April 21, 2021

Fiber may be a healthy eating buzzword, but that doesn’t mean everyone is getting enough of it. Understanding where fiber comes from, how much of it you need, and why it matters can help you meet your fiber needs and reap the associated health benefits.

Dietary Fiber: A Detailed Beginner’s Guide

What Is Fiber?

Fiber is a type of carbohydrate and is an essential nutrient for health.

While carbohydrates are broken down into glucose molecules, fiber isn’t digested, as humans lack the enzyme needed to do so.

Instead, it passes through your intestinal tract largely unchanged but feeds good gut bacteria and offers other benefits along the way.

There are two major types of fiber, each of which benefits the body in different ways:

  • Soluble fiber dissolves in water. It’s found in foods like apples, oats, beans, lentils, and blueberries. Soluble fiber, such as β-glucan, is known for its ability to lower blood sugar levels and LDL “bad” cholesterol.
  • Insoluble fiber doesn’t dissolve in water. It’s found in foods like whole grains, carrots, tomatoes, and cucumbers. Insoluble fiber is best at helping move food and nutrients through your intestinal tract, promoting bowel regularity, and treating constipation.

Consuming a healthy balance of both types of fiber is ideal and can easily be done by eating a wide variety of fiber-rich foods.

How Much Fiber Do You Need?

Nutrition surveys have found that most people who follow a westernized diet don’t meet the minimum daily fiber recommendations.

This is largely because western diet patterns tend to be heavy in animal-derived products and ultra-processed convenience foods that lack fiber.

How bad is it? According to the Institute of Medicine, basic fiber needs for most healthy adults are between 21–38 grams per day.

However, less than 5% of Americans meet these minimum daily recommendations, coming in at around 15 grams per day.

Unfortunately, this isn’t a new thing; the fiber gap has been observed for decades, particularly in the United States.

As such, national nutrition campaigns like “make half your grains whole” have previously been launched by the USDA in an attempt to draw attention to the importance of fiber from whole foods.

Still, not much improvement in fiber intake has been seen.

Health Benefits of Fiber

Getting enough fiber is a crucial piece of both acute and long-term health outcomes.

While fiber is probably best known for its role in digestion, its preventive and therapeutic reach goes much further.

Furthermore, high fiber foods are also rich in other important nutrients, like vitamins, minerals, and antioxidants that support optimal health.

Decades of science show that adequate fiber intake helps reduce the likelihood of developing chronic disease.

Some of the most well-researched health benefits of fiber are discussed below:

Supports Digestive Health

Fiber keeps your digestive system moving and supports bowel regularity by preventing constipation.

It’s also a critical nutrient for feeding your gut microbiome. The link between gut bacteria, immunity, and overall health suggests the importance of feeding your microbiome well.

A 2021 study found that vegan and omnivore diets had a more significant impact on improving the quality and integrity of the gut microbiome than a diet without fiber.

The positive impact of fiber on gut bacteria has been found in numerous other studies.

Promotes Healthy Weight Maintenance

Fiber intake from healthy whole foods is inversely associated with overweight and obesity.

Eating fiber-rich foods helps promote satiety, which can curb appetite and prevent overeating that may lead to unwanted weight gain.

Oppositely, low fiber diets are associated with having higher fat mass and a higher risk for childhood obesity.

A 2019 study found that fiber intake was a predictor of weight loss among overweight or obese adults, independent of overall calorie or macronutrient intake.

Reduces Risk for Type 2 Diabetes

Foods rich in fiber tend to result in less dramatic blood sugar and insulin responses when you eat them.

Oppositely, diets that are lacking in fiber and instead based on highly refined and processed foods are associated with a higher risk for type 2 diabetes.

A 2014 meta-analysis of 17 prospective cohort studies found that fiber intake appeared to be inversely associated with the incidence of type 2 diabetes.

Furthermore, fiber can be effective in managing and potentially even reversing type 2 diabetes for some people.

Promotes Heart Health

Fiber-rich diets are associated with a lower risk for heart disease and metabolic syndrome, a state of having a cluster of risk factors that increase the susceptibility of both heart disease and diabetes.

Fiber is known to help reduce these risk factors, such as blood pressure, blood sugar, cholesterol, triglycerides, and abdominal obesity.

It also helps keep your arteries clear from plaque buildup that can lead to heart disease.

Offers Anti-Cancer Benefits

High fiber consumption has a protective effect against some cancers.

Studies have found that fiber intake may be inversely associated with risk for breast cancer, esophageal cancer, colorectal cancer, and prostate cancer.

As fiber moves through the intestinal tract and is fermented by gut bacteria, it produces butyrate – a fatty acid thought to help prevent colon cancer.

Best Sources of Fiber

An easy way to remember the best sources of fiber is to know that this nutrient is only found in plants.

You’ll find the most fiber in whole plant foods, such as beans, peas, lentils, nuts, seeds, whole grains, fruits, and vegetables.

Here are some fantastic sources of dietary fiber and how much they offer:

  • Quinoa: 1/2 cup cooked, 3 grams
  • 100% whole wheat bread: 1 slice, 3 grams
  • Black beans: 1/2 cup canned, 9 grams
  • Lentils: 1/2 cup canned, 7 grams
  • Garbanzo beans: 1/2 cup canned, 9 grams
  • Broccoli: 1 cup chopped, 3 grams
  • Kale: 1 cup chopped, 1 gram
  • Brussels sprouts: 1 cup cooked, 6 grams
  • Carrots: 1/2 cup chopped, 2 grams
  • Banana: 1 medium, 3.5 grams
  • Apple: 1 medium, 5 grams
  • Strawberries: 1 cup, 3 grams
  • Avocado: 1 medium, 10 grams
  • Almonds: 1 ounce, 4 grams
  • Chia seeds: 1/4 cup, 12 grams

How to Increase Fiber Intake

Eating plant foods regularly, like those listed above, is the best way to meet your daily fiber needs.

Other tips for boosting fiber intake include:

  • Choosing whole fruits and veggies instead of juices
  • Substituting beans and lentils in place of meat in recipes
  • Replacing highly processed crunchy snacks with fresh produce and nuts
  • Choosing whole grains over white bread and pasta

Note that if you haven’t been used to eating many fiber-rich foods until now, it may be a good idea to gradually increase your intake.

Some people report experiencing digestive side effects such as gas, bloating, and abdominal cramping after boosting their fiber intake too quickly.

If you find that eating more fiber brings about unpleasant digestive symptoms, it may also help to drink more water to move fiber through your intestinal tract smoothly.

This has been seen in studies among people with constipation, where the condition has been best alleviated by a combination of fiber and increased water intake.

Should You Take a Fiber Supplement?

There are countless fiber supplements on the market, and you may be wondering whether you should take one to help meet your daily needs.

Fiber supplements can be beneficial in certain instances, such as for helping to gently treat acute bouts of constipation or diarrhea.

However, keep in mind that fiber supplements may reduce the absorption of certain medications.

They may also lower blood sugar levels, which could be problematic if you use medications to manage diabetes.

It’s best to speak with your doctor before using a fiber supplement in either of these cases.

Overall, supplements are not a long-term solution to meeting fiber needs.

Plus, these products don’t contain the health-promoting vitamins, minerals, and antioxidants that whole plant foods provide.

The Bottom Line

Fiber is an important nutrient that most people aren’t getting enough of in their diet.

It helps promote bowel regularity and is known to reduce the risk for several chronic diseases.

Fortunately, it’s easy to add more fiber to your diet by adding more whole plant foods, like legumes, grains, nuts, seeds, fruits, and vegetables.

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