Fiber 101

What is fiber?

Fiber, classified as a non-digestible carbohydrate, stands apart from other carbohydrates, such as starches and sugars, due to its unique behavior within the digestive system. Human cells lack the enzymes necessary to break down fiber, allowing it to pass relatively unchanged through the upper gastrointestinal tract and reach the large intestine (colon).

In the colon, intestinal bacteria, known as gut microbes, have the enzymes needed to digest many types of fiber. This microbial digestion of fiber yields short-chain fatty acids (SCFAs), which have significant documented health benefits. Despite fiber’s crucial role, a staggering 97% of people fall short of meeting their recommended fiber intake.

Where do we get fiber?

Fiber is exclusively found in plant foods, highlighting the central role a whole-food, plant-based diet plays in boosting your health. This dietary approach emphasizes the consumption of a diverse array of fiber-rich foods, including fruits, vegetables, beans, nuts, seeds, and whole grains.

Why is our diet deficient in fiber?

The Standard American Diet is predominantly composed of refined and processed foods, constituting a startling 63% of the diet. This includes soft drinks, packaged snacks, chips, desserts, and more. Animal-based products contribute 25% of dietary intake, leaving only 12% for plant-based foods. Alarmingly, nearly half of these plant-based calories are from items like French fries, meaning less than 10% of the American diet consists of essential foods such as fruits, vegetables, whole grains, nuts, and seeds.

Why is it so important that we eat enough fiber?

Fiber supports gut health by nourishing gut bacteria and producing essential SCFAs. These SCFAs are vital for overall health and well-being, including bolstering immunity and reducing inflammation.

Additionally, fiber promotes regularity, lowers cholesterol levels, reduces the risk of diabetes, and provides better blood sugar stability for those with diabetes. Fiber’s impact extends further by reducing the risk of heart disease, supporting brain health, and aiding in healthy weight management by enhancing feelings of fullness and curbing cravings.

Furthermore, fiber is associated with a decreased risk of several types of cancer, including breast, ovarian, endometrial, and colon cancer. Beyond these health benefits, fiber-containing foods offer a host of other valuable nutrients, such as vitamins, minerals, antioxidants, and phytochemicals, further enriching our diet and overall well-being.

How much fiber is recommended daily?

The Institute of Medicine recommends 25 grams of fiber for women and 38 grams for men under age 50. For those over 50, the daily recommended fiber intake is slightly lower at 21 grams for women and 30 grams for men. Currently, dietary fiber intake among adults averages about 15 grams/day.

Embracing a fiber-rich diet can be transformative for our health, and the journey begins with prioritizing whole, unprocessed foods over their processed counterparts. This diet entails incorporating fruits, vegetables, whole grains, seeds, nuts, beans, and lentils into daily meals.

How many plant-based whole foods do we need daily to meet the fiber requirements?

A plant-focused diet is crucial for meeting daily fiber requirements. Aim for 2-4 servings of fruit, 3 servings of whole grains, unlimited non-starchy vegetables, and 1 ounce of nuts or seeds daily. Starchy vegetables like potatoes, peas, and corn contribute to fiber intake. Adding beans or lentils to your meals at least 3 times a week significantly boosts fiber intake.

A diverse diet leads to a diverse gut microbiome. Research from the American Gut Project found that consuming more than 30 different plant foods weekly results in a more varied gut microbiome than those with fewer than 10 plant varieties. Additionally, those reaching the 30-plant mark exhibit higher levels of SCFAs, indicating improved gut health.

What are tips for increasing fiber?

Go low and slow when adding fiber to your diet. There is no need to rush and add all the high-fiber foods you can in one day. Instead, gradually add fiber-containing foods over time, allowing your body to adjust. Increase fiber intake as tolerated and make sure you stay hydrated. Increasing fiber intake too quickly or while dehydrated generally could lead to increased gastrointestinal symptoms. Aim for 8–10 cups of water/fluids per day to ensure you are hydrated.

Below is a high-fiber food list from the Academy of Nutrition and Dietetics to kick-start your journey toward meeting your daily fiber goals. To simplify tracking:

1. Consider tallying all the diverse plant options you consume throughout the week, including herbs and spices.
2. Aim to incorporate at least 30 different plant-based foods weekly.
3. Visualize the spectrum of plant colors as your guide and aim to create a vibrant rainbow on your plate!

Food Amount Total Fiber (grams)


Bran cereal ⅓ cup 8.6


Cooked kidney beans ½ cup 7.9


Cooked lentils ½ cup 7.8


Cooked black beans ½ cup 7.6


Canned chickpeas ½ cup 5.3


Baked beans ½ cup 5.2


Pear 1 5.1


Soybeans ½ cup 5.1


Quinoa ½ cup 5


Baked sweet potato w/skin 1 med 4.8


Baked potato w/skin 1 med 4.4


Cooked frozen green peas ½ cup 4.4


Bulgur ½ cup 4.1


Cooked frozen mixed veg ½ cup 4


Raspberries ½ cup 4


Blackberries ½ cup 3.8


Almonds 1 ounce 3.5


Cooked frozen spinach ½ cup 3.5


Vegetable or soy patty 1 each 3.4


Apple 1 med 3.3


Dried dates 5 pieces 3.3

Final Thoughts on Dietary Fiber

In summary, prioritizing fiber intake is paramount for optimal health and it's exclusively found in plant-based foods. Choosing a variety of plant foods that you tolerate will help you meet your nutrient needs, bolster long-term health, and support a healthy gut microbiome.

Fortunately, there are countless ways to incorporate plant-based foods into our meals and snacks, offering endless culinary possibilities. If you want inspiration, check out the free virtual monthly Cooking with Plants class under virtual offerings. The book Fiber Fueled (listed in references) is a total gut health program. Author and gastroenterologist Dr. Bulsiewicz writes as if he is having an easy-to-understand, personal conversation with you. It is an invaluable resource.

Learn more about Trinity Health Lifestyle Medicine and check out their virtual offerings available to patients across the state.

References:

1) Bulsiewicz, MD, MSCI, W. (2020). Fiber Fueled. Avery/Penguin Random House LLC.

2) (2016). 'The Standard American Diet is Even Sadder Than We Thought'. Forks Over Knives. (May 23).

3) Tan J, McKenzie C, Potamitis M, Thorburn AN, Mackay CR, Macia L. The role of short-chain fatty acids in health and disease. Adv Immunol. 2014;121:91-119. doi:10.1016/B978-0-12-800100-4.00003-9

4) Institute of Medicine (US) Panel on the Definition of Dietary Fiber and the Standing Committee on the


Scientific Evaluation of Dietary Reference Intakes. IV. Proposed definition of dietary fiber. In: Dietary


Reference Intakes Proposed Definition of Dietary Fiber. Washington, DC: National Academies Press (US); 2001. https://www.ncbi.nlm.nih.gov/books/NBK223591/.

5) Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press; 2005. https://doi.org/10.17226/10490.

6) McDonald D, Hyde E, Debelius JW, et al. American Gut: an Open Platform for Citizen Science Microbiome

Research. mSystems. 2018;3(3):e00031-18. Published 2018 May 15. doi:10.1128/mSystems.00031-18

7) Lloyd-Price, J., Abu-Ali, G. & Huttenhower, C. The healthy human microbiome. Genome Med 8, 51 (2016). https://doi.org/10.1186/s13073-016-0307-y