Can Fiber Fight Heart Disease?

From the publishers of the New England Journal of Medicine



In a study that must have thrilled the breakfast cereal industry, Boston researchers suggest yet another reason for eating plenty of fiber—it may lower the risk of having a heart attack.

Several smaller studies have shown a similar connection. Unfortunately, this larger study still doesn't settle the crucial question of whether fiber itself confers some protection against heart attacks.

Back in 1986, Harvard researchers asked 52,000 male health professionals to fill out detailed questionnaires about their medical histories, habits, and diets. The men completed follow-up questionnaires in 1988, 1990, and 1992.

The researchers divided the men into five groups, or quintiles, based on the amount of fiber eaten each day. Those in the lowest quintile ate an average of 12.4 grams of fiber a day, just about the national average, while those in the highest quintile ate 28.9 grams of fiber. The largest single contributor to daily fiber was cold breakfast cereal.

Over the six-year study, 229 of the men died from heart attacks or other kinds of heart disease and another 511 suffered nonfatal heart attacks. More coronary "events" occurred in the lowest fiber quintile than in the highest fiber quintile, the researchers report in the February 14 Journal of the American Medical Association.

The type of fiber also appeared to play a role. There are two kinds of fiber: Soluble fiber comes from plant gums and saps that can dissolve in the intestine's fluids, while insoluble fiber comes from the indigestible walls of plant cells. According to this study, insoluble fiber was more important than soluble fiber, and insoluble fiber from grains or breakfast cereal was more important than fiber from fruits and vegetables.
--The Editors

The Physician's Perspective
Anthony DeMaria, MD

This latest report does little to answer two questions that I, and many of you, have had for some time: What can fiber do for me, and how much do I need to eat?

We know that fiber reduces the risk of developing colon and rectal cancer. We also know that soluble fiber can lower cholesterol levels. Now the Health Professionals Follow-up researchers conclude that adding 10 grams of fiber a day reduces the risk of having a heart attack by 20 percent. That's comparable to lowering your cholesterol by 10 percent. But parts of this study make me question the conclusion.

First, the researchers didn't find any benefit from eating extra soluble fiber, which a host of other studies have shown to reduce the risk of heart disease. More important, men in the middle three quintiles had about the same risk for heart attack as the men who ate the least fiber. You would expect the men in the in-between fiber groups to have had fewer heart attacks than those who ate the least fiber but more than those who ate the most.

In an accompanying editorial, researchers from the American Health Foundation point out that the men in the top quintile smoked less, exercised more, and ate less saturated fat and cholesterol, as well as more fiber, than those in the lowest quintile. This "constellation of correlated behaviors"—not fiber alone—could be responsible for reducing the heart attack risk.

The American Health Foundation promotes a 25/25 diet—no more than 25 percent of calories from fat and at least 25 grams of fiber a day. Getting that much fiber each day isn't particularly difficult. But after ramping up fiber intake, many people have abdominal bloating, cramping, loose stools, and flatulence.

A few years back when preliminary data came out showing a connection between high fiber and lowered cholesterol, I began adding extra fiber to my diet. I didn't particularly enjoy it, especially when eating some of the high-fiber muffins we made at home. After a while, the side effects got to me and I stopped. Today, by eating lots of fruits and vegetables, I still get lots of fiber, and other important nutrients to boot, without the side effects of extra high-fiber food preparations.

As a cardiologist, I share the exasperation you may feel over conflicting research on the value of fiber in preventing heart disease. The longer I practice medicine and keep up with research, the more I believe in moderation in all things. That applies to dietary fiber. It's certainly wise to include high-fiber foods in your regular diet, but the evidence just isn't there that going overboard with fiber is worth the potential abdominal discomfort.


For More Information

bulletFor a copy of the American Health Foundation's booklet "Live Well the Low-Fat/High-Fiber Way,"  call 914-592-2600


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