Adding Fiber Cuts Heart Attack Risk, Study Finds

Typical middle-aged Americans may be able to cut their heart attack risk nearly in half by eating more fiber, even without reducing fat consumption, according to the largest study yet to analyze the effects of dietary roughage on the nation’s leading killer.

Tracking the health of more than 40,000 men for six years, researchers at the Harvard University School of Public Health found that fatal and nonfatal heart attacks were 41% less common among men who ate more than 28 grams of fiber daily, compared with those who ate less than 13 grams.

Although current federal dietary guidelines recommend that adults consume 25 grams of fiber daily, largely to reduce the risk of cancer, surveys show that average fiber consumption is only about 12 grams.

The new study offers incentive to boost fiber consumption for women as well as men, the researchers say. “We project that fiber does have the same effect on women,” said epidemiologist Eric Rimm, the study’s lead author.

“This is very important data,” said Linda Van Horn, professor of preventive medicine at Northwestern University and a member of the American Heart Assn.’s nutrition committee. “It points out what needs to be in the diet, not just what needs to be taken out. It’s quite exciting to see a big study suggesting that fiber has benefits above and beyond lowering the fat intake.”

To estimate fiber’s benefits, the Harvard researchers adjusted for other factors known to influence heart disease, such as smoking, body weight and physical activity. They also tried to correct for any inaccuracies that naturally creep into a complex study involving tens of thousands of people.

Overall, they estimated that fiber-deprived men reduced their heart attack risk by 20% to 44% for every 10 grams of fiber they added to their diet. “The true effect of fiber may be a lot stronger than what we’ve reported in this paper,” Rimm said.

While smaller studies previously found that people on a high-fiber diet have less heart disease than people who eat little fiber, many researchers questioned the fiber benefit. Such diets, they noted, also tend to be low in fat and rich in fruits and vegetables, which contain vitamins and other nutrients that may help reduce heart disease.

But the Harvard research, which appears in today’s Journal of the American Medical Assn., offers substantial evidence that the key to a high-fiber diet is the fiber itself, not other coincidental dietary factors. The Harvard researchers go even further, suggesting that the problem with the typical high-fat diet is its relative lack of fiber.

Alluding to as-yet unpublished data from this same ongoing study, the researchers write: “The positive association between saturated fat intake and coronary heart disease is almost entirely explained by lower fiber intake among the men who consumed more fat.”

Fiber is the part of a plant that the digestive system doesn’t absorb. Nearly all vegetables and fruits have some fiber, but particularly high sources include wheat bran and whole-oat cereals, legumes and leafy vegetables.

There are two basic types of fibers. Insoluble fibers such as cellulose, found in wheat bran and celery, are dense and chewy. Soluble fibers, abundant in whole oats and green peas, are soft and rather gel-like when mixed with water. In recent years, researchers observed that soluble fiber lowers elevated blood cholesterol levels, and may thus reduce heart disease.

However, the Harvard researchers found that the largest reduction in heart disease risk was among men who ate high-fiber diets containing wheat bran cereals, which contain mostly insoluble fibers.

If nothing else, Rimm said, that observation indicates that fiber’s effects go beyond cholesterol. The researchers speculate that fiber may also lower heart attack risk by altering carbohydrate metabolism and even impeding the intestinal absorption of fat. “We can’t just look at fiber as a cholesterol-lowering agent,” Rimm said.

Not all scientists agree that the Harvard researchers have resolved the fat-fiber dilemma. Nutritionist James Hill of the University of Colorado Health Sciences Center noted that people who eat more than 25 grams of fiber a day are so full that they can’t help but reduce their fat intake, and that may account for some of the reduction in heart attacks.

In an editorial in the AMA journal, researchers at the American Health Foundation, a New York-based nonprofit research group, suggest that the subjects in the Harvard study may have systematically overestimated their fiber intake and downplayed their less healthful habits, thus making fiber seem more potent than it really is.

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A Fiber Primer

Researchers at the Harvard School of Public Health have found that men can cut their heart attack risk by 41% by eating at least 28 grams of fiber a day, even if they eat a good deal of fat. Here is a look at the fiber content of some common foods:

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Food Serving size Grams of fiber Bran (100%) cereal 1/3 cup 8.5 Oats, whole 3/4 cup, cooked 1.6 Brown rice 1/2 cup, cooked 1.0 White rice 1/2 cup, cooked 0.2 Spaghetti 1 cup, cooked 1.1 Apple with skin 1 medium 3.5 Banana 1 medium 2.4 Grapefruit 1/2 large 3.1 Orange 1 medium 0.8 Kidney beans 1/2 cup, cooked 7.3 Green beans 1/2 cup 1.6 Broccoli 1/2 cup 2.2 Peas 1/2 cup 3.6 Celery 1 stalk 1.1 Lettuce 1 cup, sliced 0.9 Bean sprouts 1/2 cup 1.5

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Source: Journal of the American Dietetic Assn.