Dietitian’s Mailbag #1: It’s All About That Fiber

“When I was a kid, my mom would constantly nag me about eating enough fiber.  Now I’m 22 and she still calls me sometimes just to remind me to eat fiber.  What is fiber, anyhow, and what does it do for me?”
– Trevor F., Palo Alto

Great question.  Many of us have heard in school, from our parents, or in those weird yogurt commercials that we should make sure we’re getting enough fiber in our diet.  But most people don’t actually know why.   In the next few teeny, tiny paragraphs, I’m going to tell you what your science teachers took hours trying to explain.

We’re all familiar with carbohydrates, or “carbs” for all you cool kids—they’re one of the three major nutrients that make up all of our food, along with fat and protein.  But what the heck is fiber?  Well, guess what.  Fiber is simply a type of carbohydrate.  (Queue “The More You Know” animation)  The other types are complex carbs and simple sugars.

And for those of you who haven’t dozed off yet, here’s the fun part.  (Drumroll)  Fiber comes in two different forms, insoluble and soluble, both of which do awesome things for your body:

I like to think of insoluble fiber as a toothbrush for your digestive tract.  In fact, I’m thinking it right now.  This type is indigestible in the body, meaning it contributes no calories to the diet.  It is found in whole grains, wheat bran, and vegetables, and helps foods move through your digestive system.

Soluble fiber, on the other hand, slows down digestion, helping you to stay full longer.  This form can help lower cholesterol, minimizing risk of heart disease and allowing you to live longer so you can read more Dietitian’s Mail Bag.  Soluble fiber can be obtained through nuts, seeds, and beans, as well as some fruits and vegetables, such as strawberries, cucumbers, and carrots.

Many foods contain both forms of fiber, but in varying amounts, so I recommend eating a variety of fruits and vegetables so you get a good balance of both types.  Aim for 25 grams for women and 38 grams for men, daily.  Check out the Antioxidants Salad—one of my favorite dishes—on the menu this Thursday, which contains a whooping 20 grams of fiber!  I also love the Olive Oil Poached Salmon Salad, on Friday’s menu, offering 13 grams.

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Shira Katz, M.S., R.D. is the EAT Club Staff Dietitian
Have a question or suggestion for Shira? Email her at

3 thoughts on “Dietitian’s Mailbag #1: It’s All About That Fiber

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  1. I just bought a juicer and my family has been juicing fruits and vegetables on the weekends. Do I get any fiber in juice, or do we have to eat the fruits and vegetables?


    1. Thanks for your question, Nancy! Since skins, peels, and seeds are usually discarded when making juice, much of the fiber is lost, so whole fruits are typically richer in nutrients. The presence of fiber causes the sugars to be absorbed more slowly into the bloodstream, keeping you feeling satiated longer and less prone to eating too many calories. While it may seem easier to meet daily fruit recommendations by drinking juice, I wouldn’t recommend it as a replacement for eating whole fruit.

      Additionally, a number of studies have indicated that in fruit, most of the phytochemical (natural compounds linked to disease prevention) activity is in the peel, so when making juice, you may be losing out on some of the most beneficial parts of the fruit.

      Having said that, juice can still be part of a healthful diet! I suggest limiting intake to ~4 ounces per day.


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