Fiber: separating fact from fiction.

Fiber. Just about every food label in the supermarket now tells you how many grams of it you're getting. Ever wonder why? What's fiber good for, anyway?

"Getting rid of toxins in your colon," offers 45-year-old Tom Clark of Arlington, Virginia.

"It keeps you regular," swears 80-something Celia Katz of Rockville, Maryland. "Preventing cancer," says 52-year-old Herb Schwartz of Los Angeles.

Yes and no. The fact is, it's not only consumers, but scientists, who are uncertain about fiber's benefits. Most experts agree that certain fiber-rich foods prevent constipation and that others help lower cholesterol. But beyond that, it's pretty murky.

About the only thing researchers agree on is that we're not getting enough. (For our guide to eating more fiber, see page 10.)

Grandma called it "roughage." And of all the troubles that fiber is supposed to remedy, the one Grandma had in mind--constipation--is the one that it's most likely to fix (see box, p. 6).

Yet "regularity" is not a hot topic in the fiber field. It's cancer and heart disease that make scientists' pulses race. Most agree that diets loaded with fiber-rich foods--beans, vegetables, fruits, and whole grains--can reduce the risk of those diseases.

But is it the fiber--the largely indigestible part of the foods--or something else in them (the antioxidants or phytochemicals or who knows what) that's responsible? And if it is the fiber, which kind is best for what?

That's important for people to know, says David Jenkins, a fiber expert at the University of Toronto. "Otherwise they'll be sitting on the pot waiting for their cholesterol to drop."

THE BRAN BUBBLE

Remember oat bran? It soared to national fame--and a quick demise.

First, food companies cashed in on some preliminary studies suggesting that it lowered cholesterol. They marketed "oat bran" doughnuts, potato chips, beer, and dozens of other foods with only a smidgen of the grain.

Then the bubble burst. Frank Sacks of Harvard Medical School found that oat bran was no better at lowering cholesterol than low-fiber cereal--or, presumably, than any other low-fat food--at least in young women who had low cholesterol levels.

So-called "oat bran" foods faded away, at little loss to the public's health. But other scientists plowed ahead, conducting rigorous studies on people with higher cholesterol levels.

By 1992, even Sacks was convinced. "Oat bran lowers cholesterol slightly," he says, though he's quick to add that "cutting out saturated fat and cholesterol are far more potent ways to reduce the risk of heart disease."

BEYOND OAT BRAN

It's not just oat bran that cuts cholesterol. So do many other foods that are rich in the gummier fibers (called "soluble," because they dissolve in water).

"Oat bran, psyllium, legumes [dried beans], pectin, and guar gum all lower cholesterol," says Jenkins.

How? One theory is that some soluble fibers trap bile acids in the gut. The body makes bile acids out of cholesterol. So when soluble fiber escorts them out of the body--the liver has to pull cholesterol from the blood to make more.

As Judith Marlett, a fiber researcher at the University of Wisconsin, puts it, "the soluble fiber in oat bran drains cholesterol out of the blood."

But even though most soluble fibers lower cholesterol, says Jenkins, "it's not true of them all." Karaya and tragacanth gums, for example, appear to have a smaller effect, he notes, perhaps because they're less gummy.

And then there's the sticky question of how much you can expect your cholesterol to fall.

First, it depends on how much fiber you eat. To get a five to ten percent drop in cholesterol, says Jenkins, you'd have to eat a cup of cooked oat bran or more than two cups of cooked beans a day. The amount of psyllium in 1/3 to one cup of Bran Buds cereal would also do it, but the same amount without cereal or other food wouldn't.(1)

It also depends on your initial cholesterol level (the higher it is, the bigger the fall), which depends on how much fat you eat (the more fat, the bigger the fall). Still, last year Jenkins showed that fiber can lower cholesterol even if people are eating a very-low-fat diet.

DIET OR DRUGS

"I'd like to think that people taking fiber would do so with the best diet, high in fresh fruits and vegetables and low in fat," says Jenkins.

So he took 43 people who had high cholesterol and fed them an exemplary diet: no more than 20 percent of calories from fat, four percent from saturated fat, and 50 milligrams of cholesterol a day.(2)

All were given a hefty 50 to 60 grams of fiber a day. (The typical American averages about ten to 15 grams.) But only half the time were they fed foods like barley, beans, oat bran, and cereal made with psyllium, which are rich in soluble fiber.

The result: cholesterol levels were five percent lower when they ate the high-soluble-fiber diet. "Even people who are eating a healthy diet should know that fiber can further lower blood lipids," concludes Jenkins.

Prescriptions for cholesterol-lowering drugs--many of which have side effects--have skyrocketed in recent years, he adds. "High-fiber foods can help people who wish to do something between just a healthy diet and drugs."

FIGHTING CANCER WITH FIBER

"The National Cancer Institute [NCI] believes eating the right foods may reduce your risk of some kinds of cancer.... That's why a healthy diet includes high-fiber foods like bran cereals."

That was the message on Kellogg's 1984 All-Bran label. Ten years later, researchers still don't know if fiber reduces the risk of cancer, especially of the colon.

"Studies in different countries show that people who eat a lot of fiber from grains, vegetables, and fruit have a lower risk of cancer," says the NCI's Elaine Lanza. "But we can't say if it's fiber that's protective."

Scientists have good reason to think that fiber--especially the insoluble kind found in wheat bran--protects the colon. For one thing, wheat bran reduces the number of tumors in animals given carcinogens. And in people, bran adds bulk to the stool, which may mean that it dilutes the carcinogens that come in contact with the colon.

But so far, other results are inconclusive.

WHEATING OUT COLON CANCER

Several small trials have tested wheat bran's ability to prevent precancerous colon polyps in people who already have had a polyp removed. (Waiting for actual tumors would take too long.)

For example, Gail McKeown-Eyssen of the University of Toronto fed a low-fat diet and 35 grams of wheat bran a day to 100 polyp patients. Another 100 ate an ordinary diet. Two years later, says McKeown-Eyssen, "there was no significant difference in polyp recurrence."(3)

In a preliminary report, Robert MacLennan of Australia's Queensland Institute for Medical Research also found that wheat bran didn't cut the number of new polyps. But he did find that bran-eaters had smaller polyps with fewer precancerous cells.

Still, says the NCI's Lanza, these and other trials weren't a fair test of bran's benefits. "None have been large enough," she argues.

Lanza is hoping that her Polyp Prevention Trial, just under way, will help settle the question. She's putting 1,000 polyp patients on a low-fat diet that includes 18 grams of fiber a day for every 1,000 calories eaten, half from grains and half from five to eight servings of vegetables and fruits.

After four years, she'll compare those patients with another 1,000 on a typical American diet. In the meantime, says McKeown-Eyssen, "we need to be careful of what we mean by 'fiber.' We're not talking about adding cellulose to mayonnaise.

"Fiber is a useful shorthand for an eating pattern based on cereals and fruits and vegetables," she says. "It's not fried eggs and bacon in the morning and steak and beer for dinner."

FIBER VS. BREAST CANCER

"Finnish women have one of the highest consumptions of fat in the world," says David Rose, a cancer researcher at the American Health Foundation in Valhalla, New York. "They have a high risk of heart disease, but their risk for breast cancer is low."

Rose thinks it's fiber that protects the Finns. (At about 30 grams a day, their intake is more than double ours.)

"Anything that reduces circulating estrogen levels reduces the risk of breast cancer," he contends. Three years ago, he showed that wheat bran was one of those things.

Rose randomly gave 62 premenopausal women one of three bran supplements: wheat, oat, or corn. Each contained enough fiber to double their intakes, to 30 grams a day.(4) After two months, the women eating wheat bran--but not corn or oat bran--had lower blood estrogen levels.

Rose's results are just the beginning. It's far too early to conclude that wheat bran--or other fibers--protects against breast cancer.

"If fiber plays a role in reducing the risk of breast cancer, says Regina Ziegler, a nutritional epidemiologist at the NCI, "fiber intake should predict breast cancer risk in women."

Yet Harvard's Nurses' Health Study found no evidence that fiber protected against breast cancer, she notes. And while an analysis of 12 other studies found that women who ate more fiber were less likely to get breast cancer, there was no way to tell whether the fiber--or the beta-carotene, vitamin C, or other constituents of fruits and vegetables--reduced their risk.

"Just because fruits and vegetables are protective, it's not clear that it's because of their fiber," she says.

(1)American Journal of Clinical Nutrition 59: 1055, 1994.

(2)New Eng. Journal of Medicine 329: 21, 1993.

(3)J. of Clinical Epidemiology 47: 525, 1994.

(4)American Journal of Clinical Nutrition 54: 520, 1991.

Digesting Fiber

Americans spent $825 million last year on laxatives to treat constipation. An estimated 30 to 40 percent of people over 50 have diverticulosis. Could an apple a day keep those and other digestive problems away?

No. But a few tablespoons a day of raw wheat bran might.

"The evidence is persuasive that high doses of fiber are effective for most cases of constipation," says William Whitehead, a digestive disease expert at the University of North Carolina at Chapel Hill.

Studies show that fiber--specifically the largely insoluble fiber in wheat bran--increases stool bulk and cuts "transit time." (That's how long it takes for food to get from mouth to...well, you get the idea.) Coarse bran works better than finely ground bran, probably because it holds more water.(1)

"I recommend three tablespoons of raw bran a day," says W. Grant Thompson, a gastroenterologist at the University of Ottawa. It's not that ready-to-eat bran cereals don't work, he adds. But he's more certain that raw bran does.

Wheat bran is no panacea, though. It increases stool output and cuts transit time less in constipated people than in others.(2) "People with severe constipation are less responsive," says Whitehead.

Psyllium is an oddity. "It's all soluble fiber, but bacteria in the gut don't break it down as rapidly as they do other soluble fibers," says the University of Toronto's David Jenkins. The result: it lowers cholesterol like a soluble fiber and increases stool bulk like an insoluble fiber.

UNDER PRESSURE

A diverticulum is a pouch, or pocket, that forms in the wall of the colon. Experts believe that increased pressure pushing against the wall is to blame.

An estimated 80 percent of people with diverticulosis have no symptoms at all. But others experience constipation, diarrhea, flatulence, pain, bleeding, or inflammation (diverticulitis).

Wheat bran can help fix the constipation, but not the other symptoms.(3) Could it keep the pouches from forming? While no one's done a study to prove it, there's reason to think so.

"A high-fiber diet creates bulkier stool, which gives you a larger colon," explains Thompson. "The wider the colon, the less pressure, so it's less likely to pop pouches out."

On the other hand, cautions the University of Wisconsin's Judith Marlett, "we don't know if high-fiber diets can reverse diverticulosis. Once you have those pouches, they don't disappear."

And, she adds, patients should watch out for high-fiber foods with small

husks and seeds. "There is some concern that peanut skins and the seeds of tomatoes, cucumbers, and raspberries can lodge in the pouches."

HARD TO SWALLOW

When it comes to other digestive problems, the evidence gets skimpier.

In 1987, the American Gastrointestinal Association reported that 90 percent of its members prescribed wheat bran as a primary treatment for irritable bowel syndrome (IBS)--a poorly defined disorder with symptoms like diarrhea, constipation, abdominal pain, and bloating.

So far, studies testing bran's effectiveness have been shoddy.(4)

Like most doctors, W. Grant Thompson recommends wheat bran to treat the constipation phase of IBS. "Even if it's working as a placebo," he says, "it's a lot less harmful and expensive than a drug."

The only problem, adds William Whitehead, is that bran "tends to increase gas, at least in the beginning."

For gallstones, results are clearer: In a well-designed five-year trial, coarse wheat bran failed to prevent new gallstones in people who had already had one.(5)

(1)Am. Journal of Clinical Nutrition 34: 2460, 1981.

(2)British Medical Journal 296: 615, 1988.

(3)British Medical Journal 282: 1353, 1981.

(4)Gastroenterology 95: 232, 1988.

(5)Gut 34: 1277, 1993.

THE BOTTOM LINE

* If constipation troubles you--by itself or because of diverticulosis or irritable bowel syndrome--try adding three table-spoons of wheat bran to your food every day. Wheat bran cereals like All-Bran and fiber-rich vegetables should also help, but maybe not as much.

* If you're trying to cut your cholesterol, load up on beans, oat bran, barley, and psyllium.

* To reduce your risk of colon--and possibly breast--cancer, eat lots of vegetables, fruits, and whole grains.