Roughing It: Getting the Fiber You Need

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Medically Reviewed On: November 26, 2013

Published on: September 05, 2003


By Christine Haran

You might think that older people are the only ones who need to worry about dietary fiber, but it turns out that most of us could use more roughage. Dietary fiber not only keeps the gastrointestinal system functioning smoothly, it may also reduce risk of heart disease, colon cancer and other chronic conditions.

But that doesn't mean that everyone has to eat dozens of bran muffins every week. Dieticians say there are a lot of ways to increase fiber intake, such as eating more fruits and vegetables and more whole wheat foods and nuts. Eating different high-fiber foods also helps ensure that you are getting both kinds of needed dietary fiber: soluble and insoluble. Below, Leslie Bonci, RD, a spokesperson for the American Dietetic Association and author of The American Dietetic Association Guide to Better Digestion, explains the different kinds of dietary fiber and how to comfortably raise your fiber intake.

What is the daily requirement for fiber?
The Institute of Medicine, an agency that advises the federal government on health and science, recommends for adult women under the age of 50, 25 grams of fiber a day, and for men 38 grams of fiber a day. Over the age of 50, the requirements are 21 grams of fiber a day for women and 25 grams of fiber for men. The reason the requirement goes down with age is a function of calorie needs being less as we get older.

For children up to the age of 18, there is a formula: it is the child's age plus 5 (in grams).

Why aren't most Americans meeting these requirements?
People often assume that they can only get fiber from fruits and vegetables, and they find that to be incredibly inconvenient. People don't necessarily have fruits and vegetables in their desk drawer, so they're not getting the fiber that they need.

The other reason is that, in terms of other fiber-containing foods, people aren't always opting for a whole-grain bread or cereal, although they are available. And they aren't eating things like beans and nuts, which are sources of fiber as well.

What is the difference between soluble and insoluble fiber?
Insoluble fiber foods pull water into the body in the intestines, so they tend to make the stool a little more bulky and therefore things move through the gastrointestinal tract more quickly. So the primary role insoluble fiber plays is in promoting bowel regularity, by moving things through the gut.

Soluble fiber, on the other hand, dissolves in water. The soluble fiber actually stays in the digestive tract for a little bit longer, so it may be extremely advantageous for people who have problems with going to the bathroom too much. For people with high or low blood sugar levels, it helps to regulate their blood sugar a little bit. The other thing about soluble fiber is that it may have a role to play in lowering cholesterol. If people are using fiber to alleviate constipation, soluble fiber is not the best one to choose.

Could you name food sources for each type of fiber?
For the insoluble fiber, the best sources are bran, like a bran cereal or a bran bread. A whole wheat bread or a whole wheat cracker would be good sources, or a whole wheat cereal like Wheaties. Eating a fruit with the peel, or a baked potato with the skin, also provides insoluble fiber.

Soluble fiber is found in oat cereal, like an oatmeal or a cold oat cereal, or cooked barley or a barley cereal like Grape Nuts. Soluble fiber is found in the flesh of any fruit or vegetable, and potatoes are excellent sources, particularly sweet potatoes, of soluble fiber.

Can fiber reduce risk of heart disease?
Soluble fiber binds to bile acids, which are the precursors to cholesterol formation. So if people are eating more soluble fiber, and the soluble fiber is binding the bile acids before they can go on to form new cholesterol, that can be a tremendous advantage for helping to lower elevated cholesterol levels or for keeping cholesterol levels more normal.

There actually is a heart health label on certain products that are high in soluble fiber such as an oat cereal.

Does fiber reduce the risk of colon cancer?
There has been some question about the benefit of fiber for lowering the risk of colon cancer, because the studies have not been conclusive. Regardless, the fact that people are eating things with fiber, and fiber is acting as the body's vacuum cleaner to move things through, contributes to a smaller chance that the tissues of the intestine will be exposed to chemicals and carcinogens that could potentially be in food. So there still is an advantage to upping one's fiber intake to keep the gut healthy.

How can fiber help with diabetes management?
With the soluble fibers, the oat and the barley type of fiber, there may be a benefit in helping to regulate blood glucose levels. People get a more even blood glucose response over the course of a day, which although it doesn't prevent the disease, helps to manage symptoms. So having more soluble fiber in the diet for a diabetic can certainly help to achieve maximal blood glucose control.

What other health benefits can fiber provide?
One of the concerns that will affect the majority of Americans as we get older is diverticular disease. The diverticula are little pockets that form in the large intestine. If something gets caught in them, they can get inflamed, which causes diverticulitis.

Because fiber moves things through the intestine more rapidly, people who eat it are less likely to have particles get caught in the diverticulum. So fiber definitely has a role to play in lowering the risk of diverticular disease.

Fiber is also used to help with constipation. Although people feel like they have to run to a drugstore to buy an over-the-counter fiber supplement, foods actually work beautifully in that regard. But people need to establish a schedule and gradually increase on their fiber intake and fluid intake simultaneously, and make sure they're picking the right kind of fiber. Somebody needs to pick insoluble fiber to help with constipation, so if they just eats oats alone, chances are they're not going to feel better.

Additionally, there's been a lot of interest in the role of fiber in helping to manage weight. First of all, foods that have soluble fiber in them tend to take longer to empty from the gastrointestinal tract, so people feel fuller for longer. Also, because insoluble foods with fiber tend to draw water into the intestine, again, there is a feeling of fullness, so we can go longer between meals without feeling like we need to eat. Thirdly, our bodies have to work a little bit harder to break down fiber; even though fiber is not a digestible nutrient for the human body, we still have to break it down and that process alone expends more calories, which may also contribute to a more calories being burned over the course of the day.

So ideally, for weight management, both types of fiber are desired. And in general, when we talk about fiber needs, the ideal scenario would be to have a mix of both types of fiber over the course of the day, not just somebody saying, "Well, I'll just eat bran to the exclusion of all else."

What happens if people don't add fiber to their diet gradually?
If people start to drastically increase their fiber, normally what ends up happening is they either become incredibly constipated or, in some cases, feel like they just can't stop going to the bathroom; it's physically not comfortable.

I recommend that people figure out where they are currently in terms of fiber intake and very gradually increase their intake from there by up to 5 grams. If somebody's starting out with an intake of 10 grams of fiber a day, they could increase it to 15 grams and do that for the course of a week and then gradually increase it from there.

Five grams of fiber might be the equivalent of two pieces of fruit or two one-half cup servings of vegetables or the equivalent of two slices of a whole grain bread, like a 100 percent whole wheat bread or a half of a cup of a high-fiber cereal such as All-Bran. So it really doesn't require volumes of food to get 5 grams of fiber.

The other thing is that as people increase their fiber intake, it's also a good idea to drink a little bit more fluid, because that helps to prevent some of the constipation that can occur when people overload on soluble fiber.

People should also spread their fiber intake out over the course of the day. Every meal presents itself with an opportunity, from cereal to the bread choices at lunchtime to fruits and vegetables or soup at dinner. There's always a way to sneak in extra fiber.

What are some easy ways to eat more fiber?
If people change their snack item, that can help. For instance, instead of having pretzels as a snack, have popcorn, because it has more fiber in it. Or instead of having chips as a snack, to do a trail mix with something like an oat cereal and put some nuts in there, because nuts have fiber as well.

A lot of people say vegetables are too time-consuming, but throwing a handful of frozen vegetables into a jar of spaghetti sauce is a great way of boosting up the fiber and it doesn't take any time at all.

People often believe that if you have a vegetable in a frozen or canned form, you don't get the fiber, but it's actually identical in terms of the fiber content. When a fruit is canned, however, the fiber content is lower, because the skin or peel is removed. So a canned fruit is going to be lower in fiber, but a canned vegetable or a frozen vegetable will be equivalent.

Are there any times when you recommend fiber supplements?
If somebody is really having a hard time getting their needs met via food, or perhaps somebody travels a lot and there's limited availability of fruits and vegetables, then a fiber supplement might be warranted. I would always say that, even if that is the case, we're still looking at meeting some of the fiber needs through food and not at relying on a fiber supplement exclusively as a way of getting the needs met.

How can the Atkins diet affect fiber intake?
For the most part, the Atkins diet is fiber-free or has minimal fiber. People aren't eating fruit, they're eating very minimal vegetables, they're not eating any of the starchy foods that would have fiber in them and protein is not a fiber source for the body. Although people are losing weight, they're doing their gastrointestinal tract a tremendous disservice, because the body doesn't have the fiber it needs.

Because we're looking at the role of fiber as a vacuum cleaner helping to clean out the gut, so to speak, if somebody doesn't provide those foods into the diet daily, we worry about the long-term effects for gastrointestinal health.

The other thing about fiber-containing foods, for the most part, is that they are also a source of fluid for the body. If you're eating less of them, then that also contributes to feeling a little bit more constipated, because the body might not be getting enough fluid.

Are there any other long-term effects of a low-fiber intake?
The increased risk of diverticular disease is probably the biggest one across the board. We are also at increased risk of developing constipation as we get older, because if we're not routinely making our bowels work well, it gets progressively harder, because there is some degree of change in gastrointestinal function with age. If we're looking at keeping the intestines healthy, one of the best ways of doing that is making sure that we're getting that nutrition prescription for fiber in every day.