Fiber: Soluble & Insoluble

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Dietary fiber is a plant-based nutrient made of substances such as cellulose, lignin, and pectin. These substances are not digested by the digestive system within the body. Rather than being digested, they are passed through the digestive system, through the colon, and then out of the body. Dietary fiber is most commonly found in fruits, vegetables, whole grains, and legumes. Fiber intake is important in order to help normalize bowel movements, maintain bowel health, lower cholesterol levels, maintain blood sugar levels, and maintain a proper and healthy weight. 

There are two different types of fiber: soluble and insoluble. Both are indigestible. Soluble fiber is attracted to water, causing it to dissolve and form into a gel type substance for digestion. This allows for slower digestion to occur. In addition, it binds with fatty acids which allows for blood cholesterol and blood glucose levels to lower. Soluble fiber is most commonly found in oat bran, barley, nuts, seeds, lentils, peas, and a variety of fruits and vegetables. 

Insoluble fiber promotes movement through the digestive system and increases the bulk of the stool. It passes through the body largely intact, unlike soluble fiber. It makes stool softer and heavier which is beneficial for those who have issues with constipation or irregular bowel movements by providing easier bowel movements. In addition, it can help remove toxic waste through the colon rather quickly and prevent colon cancer by keeping an optimal pH level in the gastrointestinal tract. Insoluble fiber is most commonly found in wheat bran, vegetables, and whole grains. Fibrous foods are also able to keep the body full and satiated for longer periods of time because the insoluble fiber remains in the digestive system for a longer amount of time. This prevents the brain from signaling the body to eat which can help with weight loss by reducing the temptation of overeating. 

Insoluble fiber does not need to be prioritized over soluble fiber or vice versa. As long as the total fiber consumption meets the daily requirements, this is the important part. It is recommended to consume, at minimum, 14g of dietary fiber for every 1000 calories consumed. About 25g for women, 38 for men ages 50 or younger, and 21g for women and 30g for men ages 51 or older. Focus on meeting this requirement throughout the day through high fiber foods, such as wheat or oat bran, psyllium husk, and flax seed. With about 5 servings of fruits and vegetables and 6 servings of whole grains, the daily requirements can easily be achieved. 

Insoluble

Wheat bran

  • Wheat products: pasta, bread, etc.

Oat bran

  • Use for hot cereal, add in yogurt, or replace as breadcrumbs

Beans/Legumes

  • Lima, pinto, kidney, garbanzo, etc. 

Vegetables

  • Greens (spinach, lettuce, kale, etc.)

  • Green beans

  • Bell pepper

  • Eggplant

  • Celery

  • Onions

  • Okra

Turnips

Seeds/nuts

  • Walnuts

  • Sunflower seeds

  • Flaxseeds


Soluble

Oat bran

Barley

Peanuts

Nuts

  • Almonds, brazil nuts

Seeds

  • Flaxseeds

  • Sesame

  • Sunflower

Fruits

  • Berries (especially raspberries)

  • Citrus fruits

  • Apples

  • Fig

  • Bananas 

  • Apricot

Sweet potato

Turnips

Pears

Beans/lentils 

Carrots

Vegetables

  • Brussel sprouts

  • Avocados

  • Broccoli

  • Zucchini 

Todd Bauer