Lauren Harris-Pincus

MS, RDN

Top 10 Fiber FAQs

Read up on the top questions answered by our Dietitian

What is fiber?

Fiber is the general name for certain carbohydrates — usually parts of vegetables, plants, and grains — that the body can’t fully digest. While fiber isn’t broken down and absorbed like other nutrients, it still plays a key role in good health.  Fiber is probably best known for its ability to help keep your digestive system moving, but there are other benefits associated with eating a high fiber diet, like helping to promote a feeling of fullness.  With some planning, and a little knowledge about a proper diet, you can realistically meet your fiber needs and unlock the benefits that fiber can have for your wellbeing.

What are the different types of fiber found in food?

Fiber is commonly classified as soluble, which dissolves in water, or insoluble, which doesn’t dissolve in water.

(1) Soluble fiber is the type of fiber that dissolves in water and can help lower blood cholesterol.   
(2) Insoluble fiber
doesn’t dissolve in water. This type of fiber adds bulk to foods which helps it move through your digestive system. At the start, that means it helps you feel full (hello, hunger pangs!). And later, it helps keep you regular and comfortable (phew!).

How does fiber function in the body?

Soluble fiber is kind of “gummy”, it attracts water and turns to gel during digestion so it slows down the speed of absorption of carbohydrates and sugars. It also binds to substances called bile acids which help to lower cholesterol.

Insoluble fiber helps to bulk up your poop (Yes, I said it!) and promotes movement through your digestive system. Bye, bye constipation.

What is constipation and why does fiber help?

Constipation is a condition in which you have fewer than three bowel movements in a week, and your stools are hard, dry, and small, making them painful and difficult to pass. There are many factors that contribute to constipation including medications, dietary changes and reduced fluid intake. Adequate hydration and fiber, especially insoluble fiber, can help to prevent and improve constipation. Fiber needs water to keep things moving through!

What foods have soluble fiber?

Lots! Some include:

  • Apples
  • Citrus Fruits
  • Whole Grain Oats
  • Oatmeal
  • Barley
  • Beans
  • Dried Peas
  • Brussels Sprouts
  • Mangoes
  • Ready-to-Eat Cereal
What foods have insoluble fiber?

There are many! A few commonly enjoyed examples are:

  • Spinach, Kale
  • Bell Peppers
  • Wheat Bran
  • Whole Grain products
  • Onions, Garlic
  • Beans, Lentils
  • Popcorn
  • Broccoli
  • Carrots
  • Ready-to-Eat Cereal
How much fiber do we need per day?

According to the Dietary Guidelines for Americans, the adequate intake for fiber is 14 g per 1,000 calories, or approximately 25 g per day for women and 38 g per day for men on average.

Which foods have the most fiber?

Fiber is found predominantly in whole grains, fruits, veggies, nuts, beans and seeds.
Some examples of higher fiber options are:

  • Original Fiber One cereal (1/2 cup)= 14 grams
  • Raw raspberries (1 cup)= 8 grams
  • Raw blackberries (1 cup) = 7.6 grams
  • Pistachios (1/4 cup)= 3.2 grams
  • 1 medium apple= 3 grams
  • 1 large baked potato with skin(3-4 inch diameter)= 6.9 grams
  • Pistachios (1/4 cup)= 3.2 grams
  • 1 medium apple= 3 grams
  • Cooked and chopped frozen broccoli (1 cup)= 5.5 grams
  • Cooked, whole grain spaghetti (51% whole wheat pasta- 1 cup)= 5.3 grams
  • Cooked lentils (½ cup)= 7.8 grams
  • Canned red kidney beans (1/2 cup)= 8 grams
  • Chia seeds (1 Tablespoon)= 4 grams
What happens if I don’t get enough fiber?

9 out of 10 Americans don’t consume the recommended amount of daily fiber and 16% suffer from constipation! We have some work to do. Diets low in fiber usually feature more highly processed foods and lack sufficient fiber rich fruits, veggies, whole grains, nuts, beans and seeds. For this reason, diets inadequate in fiber not only contribute to constipation but may have an effect on overall health. If you are not used to consuming high fiber foods, start slowly to make sure your tummy tolerates the change in your eating habits and be sure to increase your fluid intake as well.

Is it possible to consume too much fiber?

Technically, yes, it’s possible. Too much fiber can cause effects such as gas, bloating and abdominal pain. Even constipation can be a side effect of too much fiber with not enough water. Since fiber soaks up water like a sponge, you need adequate hydration to keep things moving. When increasing fiber make sure to do it slowly. Try adding an extra serving or two of high fiber foods for a week to see how it goes and increase from there. Start with food sources of dietary fiber like cereal, whole grains, fruits, veggies, nuts, seeds and beans.

References

Questions and answers on dietary fiber, U.S. Food and Drug Administration https://www.fda.gov/food/labelingnutrition/ucm528582.htm

Dietary Guidelines for Americans 2015-2020, Eight Edition https://health.gov/dietaryguidelines/2015/guidelines/

USDA Food Composition Databases https://ndb.nal.usda.gov/ndb/