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Getting to Know Fiber… Again (Part 1)

Amy Campbell

January 31, 2011

Doctors, dietitians, and television commercials constantly tell us to eat more fiber, and many of us are tired of hearing it. But it’s one message that doesn’t seem to go away — and for good reason. Most Americans don’t get enough fiber. If we did, we might not be dealing with as many health issues.

No, fiber isn’t a cure-all or even a medicine, but when you stop and think about it, it’s pretty remarkable what fiber can do. By the time you read this, the US Department of Agriculture and the US Department of Health and Human Services will just have announced the new 2010 Dietary Guidelines for Americans, which come out every five years. We’ll see what they have to say about fiber. In the meantime, let’s revisit our old friend that does more for us than we realize.

What Is Fiber, Anyway?
Fiber is kind of a standalone in the world of nutrition. It’s actually a carbohydrate, but (unlike starches and sugars) we can’t digest it very well. Fiber is made up of glucose units similar to those in starches and sugars, but in fiber, the units are bonded in such a way that we can’t break them apart in the digestive tract. We don’t have the enzymes to do this. So this means that fiber pretty much stays intact as it travels through the gut.

However, once fiber reaches the large intestine, it can be metabolized or fermented by intestinal bacteria, the “friendly flora” that use fiber for energy. (You can thank the bacteria for any feelings of [ahem] “gassiness” that you might experience after eating that bowl of bran flakes.) Some fiber isn’t fermented by bacteria, however, and simply passes right through us.

Insoluble Fiber: Nature’s Broom
Dietitians generally talk about two types of fiber: insoluble and soluble. That breakdown is actually not quite accurate, but we’ll get to that another time. Insoluble fiber is usually what most people think of when they hear the word “fiber.” Here are the different types of insoluble fiber:

• Cellulose is a major source of dietary fiber in our diets. It’s a carbohydrate that makes up cell walls in plants and is responsible for giving plant stems, leaves, and roots their structure and “toughness.” Cellulose is insoluble in water, meaning that it doesn’t dissolve. Only certain animals, such as cows and horses, can break down cellulose. For this reason, most people refer to insoluble fiber as “roughage” or “bulk.”
• Hemicellulose is also a carbohydrate found along with cellulose in plant cell walls. While cellulose is made up of glucose, hemicellulose is made up of other sugars, such as xylose, mannose, and galactose (sugar alcohols, such as xylitol, are made from hemicellulose).
• Lignans are plant chemicals. Some of them have an estrogen-like function; they’re also called phytoestrogens. Lignans also act like antioxidants. These natural chemicals are thought to play a role in cancer prevention. Flaxseed and sesame seeds are particularly high in lignans.

What it does. I’ve heard insoluble fiber referred to as “nature’s broom.” As insoluble fiber travels through your digestive tract, it binds to water. This makes stools bulkier and softer, helping to prevent constipation and diverticulosis, a condition in which pouches form in the intestinal wall. Diverticulosis can lead to diverticulitis, which is a painful inflammation of these pouches. Here’s what insoluble fiber can do for us:

• Prevent constipation and diverticulosis
• Prevent hemorrhoids
• “Normalize” bowel movements
• Possible help to lower the risk of colon cancer (the jury is still out on this)
• Decrease exposure to toxins and other harmful substances in the intestines
• Help you feel full so that you eat less

Food sources. It’s pretty easy to get insoluble fiber in your diet. And chances are you like at least some of these foods!

• Whole grains: popcorn, whole wheat pasta and bread, wheat germ, rye bread
• Wheat bran (add to cereals and homemade muffins)
• Nuts: almonds, chestnuts, peanuts
• Seeds: sunflower seeds, sesame seeds, flaxseeds
• Vegetables: leafy greens, broccoli, parsnips, peas
• Fruits: the peel contains insoluble fiber, so eat apple and pear peels
• Legumes: kidney beans, white beans, lentils, soybeans

How much? Your total daily fiber intake should be about 14 grams of fiber per 1,000 calories, or somewhere between 25 and 35 grams per day. Most people take in only about 13 grams per day, so there’s room for improvement.

More fiber fun next week!

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