When you are seeking to improve our gut health and overall wellness through functional medicine, fiber becomes a vital component of the process. Fiber is a type of carbohydrate found in plant foods, but unlike other carbohydrates, the human body can’t digest it. As it passes through the body’s digestive system, it performs many important functions. 

Fiber slows the rate at which food enters your bloodstream and increases the speed at which food exits your body through the digestive tract. It can help lower cholesterol, blood sugar, and insulin levels. It helps eliminate toxins, remove excess estrogen, and balances hormones. It can help prevent obesity and chronic disease, and it reduces the risk of breast and colon cancer. It makes vitamins and minerals, and acts as a food source for the beneficial bacteria that live in the digestive tract. You need fiber to keep you healthy from top to bottom. 

Types of Fiber

Dietary fiber comes from plant foods, including fruits, vegetables, legumes, nuts, seeds, and grains. Plant foods contain two types of fiber—soluble and insoluble.

Soluble Fiber

Soluble fiber dissolves in water and becomes gel-like, which slows down the rate at which food hits the bloodstream, slowing down digestion of glucose, producing a feeling of fullness, and helping with weight control. It decreases the absorption of sugars and fats, helping manage blood sugar and blood fat levels. Soluble fiber serves as a food source for the beneficial bacteria that live in the digestive tract. 

Insoluble Fiber

Insoluble fiber absorbs water, but does not dissolve in water. It helps move food and waste products through the digestive system, promoting regular bowel movements. It provides bulk to the stool and is beneficial in preventing constipation, hemorrhoids, and diverticulitis.

Symptoms of Insufficient Fiber Intake

The Dietary Reference Intake for dietary fiber (soluble and insoluble fiber, combined) is:

Females, age 18-50: 25 grams per day

Females, ages 51 and above: 21 grams per day

Males, ages 18-50: 38 grams per day

Males, ages 51 and above: 30 grams per day 

Consuming too little fiber can cause major repercussions throughout the body, including: 

  • Constipation
  • Diet-related nausea
  • Excessive gas
  • Fatigue or weakness
  • Frequent hunger
  • Hemorrhoids
  • Hypercholesterolemia (high cholesterol)
  • Hyperglycemia (high blood sugar)
  • Increased risk of developing gallstones
  • Irritable bowel syndrome (IBS)
  • Loss of appetite
  • Overeating
  • Upset stomach
  • Varicose veins

Conditions that can Benefit from Soluble Fiber:

  • Cancer (prevention)
  • Excess weight
  • Hypercholesterolemia (high cholesterol)
  • Hyperglycemia (high blood sugar)
  • Hypertension (high blood pressure
  • Irritable bowel syndromes
  • Metabolic syndrome
  • Overweight or obesity

Conditions that can Benefit from Insoluble Fiber:

  • Constipation
  • Loose stools

Sources of Fiber

Dietary fiber comes from plant foods, including fruits, vegetables, legumes, nuts, seeds, and grains. Most plant-based foods contain both types of fiber. For example, the inner portion of an apple contains soluble fiber and the peel is insoluble fiber. 

In order to get the full benefits of fiber, plant foods must be eaten in their whole form, or close to their whole form. 

Plant Sources of Soluble Fiber

  • Apples
  • Apricots
  • Artichokes
  • Asparagus
  • Avocado
  • Bananas
  • Barley
  • Beans (black, lima)
  • Blackberries
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Carrots
  • Dark, leafy greens
  • Flaxseed
  • Legumes
  • Lentils
  • Nuts
  • Oat bran
  • Okra
  • Oranges
  • Pears
  • Peppers
  • Prunes
  • Psyllium
  • Squash
  • Sweet potatoes

Plant Sources of Insoluble Fiber

  • Bananas
  • Beans (black, kidney, navy)
  • Bran
  • Broccoli 
  • Brown rice
  • Brussels sprouts
  • Carrots
  • Cauliflower
  • Celery
  • Corn
  • Cucumbers
  • Grains
  • Lentils
  • Okra
  • Peas
  • Potatoes (with skin)
  • Prunes
  • Spinach
  • Tomatoes
  • Wheat bran

Increasing Your Fiber Intake

The Institute for Functional Medicine recommends that adults consume about 25 – 35 grams of fiber daily from their food. However, the average American adult eats about half that amount. Tips for incorporating more fiber into your diet include:

  • Try to eat 5 – 10 servings of fresh vegetables or fruit per day. A serving is half a cup of cooked vegetables, one cup of raw or leafy vegetables, or a medium piece of fruit.
  • Including fresh vegetables with each meal and snack is a great way to make sure you reach your daily goal.
  • Choose whole grain rice, breads, and pastas over products made with refined or white flour.
  • Get creative with substitutions. If a recipe calls for animal protein, try making the dish with beans or legumes instead. (This works well with chili, soups, and stews.)
  • Swap juices for smoothies, using the same ingredients. While fresh fruit and vegetable juices contain vitamins and minerals, the fiber is lost in the juicing process. Blending the ingredients into a smoothie will produce a similar taste without losing the beneficial fiber.

Remember: adding too much fiber or adding fiber too quickly can cause bloating, gas, cramps, and diarrhea. When first starting to add fiber into your diet, try adding 5 grams daily in 2-week intervals until you hit your target intake. 

Drink a lot of water when you ingest a large amount of fiber so that you do not become constipated.