Getting to Know Fiber… Again (Part 3)


Has all this talk[1] about fiber[2] got you thinking about your fiber intake? I know, it isn’t all that exciting. Fiber kind of lost its luster a while ago. In the 1980’s the hype was that a high-fiber diet could protect against colon cancer. But less than twenty years after that, two studies came out hinting that this wasn’t the case because the participants eating high-fiber diets had no fewer precancerous polyps than the people eating low-fiber diets.

All is not lost, however. The American Institute for Cancer Research still maintains that high-fiber foods may protect against colon cancer. So why wouldn’t we want to eat more of these foods? Break out the bran flakes!

Isolated Fiber: Is That Really Fiber in My Ice Cream?
If you thought fiber was just limited to being insoluble or soluble, think again. There’s yet another type of fiber that has snuck its way in to foods that you would never think could have fiber. Maybe you’ve noticed some of these foods in the grocery aisles.

First, there’s intact (dietary) fiber, which we’ve talked about over the past two weeks. Intact fiber is fiber that’s naturally found in foods, such as in beans and apples. Isolated (added) fibers are fibers that come from food but are processed by food manufacturers to get just the good stuff out. These fibers are actually types of soluble fiber. But because they’re not “gummy” like other soluble fibers, they work differently than, say, the soluble fiber in oats or barley. For example, they don’t work to lower blood cholesterol. Here are examples of isolated fibers:

You may have heard these terms or even seen them on an ingredient list, but what are they? Below are three isolated fibers and what they are.

Inulin. We have to be careful here — this is “inulin”, not “insulin.” Inulin is a natural fiber that’s found in many foods, including leeks, bananas, onions, asparagus, Jerusalem artichoke, and chicory root. You may think you’re not eating chicory root, but you probably are if you’re eating yogurt, breakfast bars, or sweeteners that contain added fiber. Inulin is a “prebiotic” because it serves as food for good bacteria in the large intestine. The downside? Too much inulin can cause gas, cramping, and diarrhea. On the other hand, it is resistant to digestion, so it won’t affect your blood glucose (although the food that it’s in will likely contain carbohydrate). You’ll know if a food contains inulin if you see “chicory root extract” on the ingredient list. Why not eat natural sources of inulin? Fill up on asparagus, onions, leeks, and garlic.

Maltodextrin. Maltodextrin is a carbohydrate called a polysaccharide. It’s actually a starch from corn, potatoes, rice, or wheat and it’s used frequently as a food additive. Food companies use maltodextrin as a type of fiber in the form of “resistant” maltodextrin. This is maltodextrin that’s been altered by heat, enzymes, or acid to prevent it from being broken down in the digestive tract. Resistant maltodextrin has no flavor or odor and can make sweeteners taste sweeter and seem more like sugar. You might find resistant maltodextrin in desserts such as ice cream. There are no reported side effects but if you have celiac disease, you should be careful about eating foods that contain this ingredient.

Polydextrose. Polydextrose is a food additive that is made from dextrose, a type of sugar. It also contains sorbitol and citric acid. It’s very low in calories, so food manufacturers like to use it in reduced-calorie or reduced-carbohydrate foods. You may see polydextrose in foods like puddings, gelatins, and low-fat ice frozen desserts. Polydextrose isn’t digested, but when it reached the large intestine, some of it is fermented by bacteria. It can actually help promote GI health by bulking up and softening stools, and slowing transit time. The downside? Gas, cramps, diarrhea (similar to side effects of sugar alcohols).

In a Nutshell
The Nutrition Facts label lists dietary fiber, but it doesn’t tell you how much is from intact fiber and how much from isolated fiber. Isolated fiber isn’t “bad,” but it doesn’t seem to have the same health benefits as fiber from more natural sources. For example, it’s unlikely that isolated fibers will help to lower cholesterol or blood glucose. On the other hand, if you’re constipated, these foods may help.

You’ll know if your food contains isolated fiber if:

For now, aim to get most of your fiber from the whole-food sources that we’ve been talking about over the past couple of weeks. And don’t rely on chowing down on “high-fiber” ice cream treats to meet your daily fiber needs!

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Amy Campbell: Amy Campbell is the author of Staying Healthy with Diabetes: Nutrition and Meal Planning and a frequent contributor to Diabetes Self-Management and Diabetes & You. She has co-authored several books, including the The Joslin Guide to Diabetes and the American Diabetes Association’s 16 Myths of a “Diabetic Diet,” for which she received a Will Solimene Award of Excellence in Medical Communication and a National Health Information Award in 2000. Amy also developed menus for Fit Not Fat at Forty Plus and co-authored Eat Carbs, Lose Weight with fitness expert Denise Austin. Amy earned a bachelor’s degree in nutrition from Simmons College and a master’s degree in nutrition education from Boston University. In addition to being a Registered Dietitian, she is a Certified Diabetes Educator and a member of the American Dietetic Association, the American Diabetes Association, and the American Association of Diabetes Educators. Amy was formerly a Diabetes and Nutrition Educator at Joslin Diabetes Center, where she was responsible for the development, implementation, and evaluation of disease management programs, including clinical guideline and educational material development, and the development, testing, and implementation of disease management applications. She is currently the Director of Clinical Education Content Development and Training at Good Measures. Amy has developed and conducted training sessions for various disease and case management programs and is a frequent presenter at disease management events.

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