Fiber: Top Nutrient for a Good Mood

By Ruth Capistrano, Master’s Student and Dietetic Intern

With COVID-19 still in the air, it’s hard to not give in to feelings of stress and anxiety.  While these external factors are beyond our control, what we choose to eat and put in our bodies is very much within our grasp.  Our diet has shown to affect our mood, with many studies promoting fruits, vegetables, and whole grains to lessen anxiety and depressive symptoms.  Recently, researchers have been focusing specifically on dietary fiber and how it can improve our mood.

What Happens When You Eat Fiber?

The term, dietary fiber, refers to carbohydrates from plants that cannot be digested, such as resistant starch.  Fiber, therefore, remains intact, passing through the digestive tract until it reaches the large intestine.  The trillions of bacteria residing in the large intestine feed off the fiber in a process called fermentation.  The most dominant by-products of fermentation, short-chain fatty acids (SCFAs), are vital in the mechanisms described below.

How Does Fiber Improve Your Mood?

Researchers are currently in the process of fine-tuning the connection between fiber and mood.  Clinical studies so far have shown that the SCFAs produce neurotransmitters, activate receptors in the brain, and reduce inflammation.

1. Production of Neurotransmitters

The gut-brain axis is the communication network between the gut microbiota and the brain.  It enables the SCFAs to produce the following neurotransmitters:

Tryptophan and Serotonin

Tryptophan is the precursor to serotonin, a neurotransmitter that helps regulate mood.  Because our bodies do not make tryptophan, it can only be obtained from either diet or certain bacteria in the gut.

C-aminobutyric Acid

Reduced levels of this neurotransmitter lead to anxiety disorders and is observed in depression.  While it can be synthesized in our bodies, it is also produced by several bacterial strains. 

2. Activation of G-Protein Coupled Receptors (GPCRs)

SCFAs activate the GPCRs, which are membrane proteins in the brain.  Activated GPCRs increase the release of norepinephrine, a neurotransmitter that is effective in reducing depression.  Some antidepressants increase the concentrations of norepinephrine for this very reason.

3. Reduction of Inflammation

Low levels of dietary fiber result in the development of chronic inflammatory diseases such as colorectal cancer, intestinal bowel disease, and obesity.  Studies have shown depression to be related to inflammation as well.  The proinflammatory cytokines responsible for inflammation decrease the production of serotonin and dopamine.  Dietary fiber can alleviate chronic inflammation by reducing intestinal pH and membrane permeability, ultimately preventing the production of proinflammatory cytokines.

What are Sources of Fiber?

Foods that are considered good sources of fiber are fruits, vegetables, whole grains, legumes (beans, peas, lentils), nuts and seeds.  Processed and refined foods are discouraged, as they have lower levels of fiber.

How Much Fiber Should You Eat?

According to the Institute of Medicine, the fiber recommendation for individuals 50 years old or younger is 38 grams and 25 grams for men and women, respectively.  For those who are 51 years old or older, the recommendation decreases to 30 grams and 21 grams for men and women, respectively.

Increase the amount of fiber you eat gradually to avoid abdominal bloating and cramping.  Additionally, match your higher intake of fiber with a higher intake of water.  Fiber has the tendency to absorb water, so keeping yourself hydrated will soften your stool and ease overall transit.

How Can You Increase Your Fiber Intake?

  • Pick recipes that allow you to incorporate more legumes into your dish. Elle’s minestrone soup recipe is a great example!
  • Choose whole-grain products, instead of refined grains.  At least half of your grains should by whole grains. Try Alyssa’s whole wheat berry pancake recipe for a fiber-rich breakfast!
  • Search for the words, “whole grain,” “bran,” or “fiber” on the product labeling when grocery shopping.
  • When selecting breads, look at the ingredient list and see if whole wheat, whole wheat flour, or another whole grain is listed first.
  • When selecting high-fiber cereals, look at the nutrition facts label and choose products with 5 or more grams of fiber per serving.
  • Experiment with brown rice, wild rice, barley, whole-wheat pasta, or bulgur wheat.
  • Eat five or more servings of fruits and vegetables a day. Elle’s summer salmon salad makes this exceptionally easy!
  1. Swann OG, Kilpatrick M, Breslin M, Oddy WH.  Dietary fiber and its associations with depression and inflammation.  Nutr Rev.  2019;78(5):394-411.  DOI:10.1093/nutrit/nuz072.
  2. Dietary fiber: Essential for a healthy diet.  Mayo Clinic.  Accessed June 24, 2020.

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