A bowl of spicy black bean soup with brown rice and a slice of whole wheat bread–it’s comfort food rather than high cuisine, but the dish is rich in fiber and gets high marks for nutrition.
Fiber comes in many forms–beans, lentils, chick peas, whole grains, brown rice, fruits and vegetables–and it’s good for you. For heart disease, cancer, high blood pressure, obesity and diabetes–the five major killers in our country–fiber-rich foods have proven benefits.
The Institute of Medicine recommends that you eat 25 to 38 grams of fiber a day, depending on your gender and size, but you’ll get what you need without counting if you eat a balanced diet with five or more servings a day of fruits and vegetables and seven servings of whole grain breads or cereals. The dish described above, for example, provides about half the daily requirement: 15 grams for a cup of beans, 2 grams for a half cup of rice and 2 grams for a slice of whole grain bread. The average American gets less than that amount in a day–only 12 to 17 grams.
Dietary fiber comes from the indigestible walls of plants–fruits, vegetables, legumes or grains. While these cell walls are edible, they resist stomach acids and make it to the bowels intact. Once known as “roughage” or “bulk,” fiber has long been recognized for its role in maintaining bowel regularity but only recently for its other health-giving qualities.
Plants are generally rich in vitamins, minerals and health-promoting phytochemicals. And if you eat a lot of plant foods, you won’t have as much room for the saturated fats that are found in animal products. Recent research has revealed that there are also benefits to be gained from the fiber itself.
Lowers Heart Disease Risk
A study of 40,000 male health professionals and a related large study of female nurses found that subjects with a high daily intake of fiber had a 40 percent lower risk of coronary heart disease than those with the lowest intake of fiber. Cereal fiber was found to be particularly beneficial.
For every 10 grams of fiber you add to your daily diet, your risk of dying from a heart attack is reduced by 27 percent, according to a more recent study published in the Archives of Internal Medicine [February 23, 2004].
One reason for the beneficial effect is that fiber reduces the amount of cholesterol absorbed from food. High-fiber foods also have a positive effect on blood pressure. And because they’re filling and relatively low in calories, they play a role in weight control.
By slowing the absorption of food in the bowels, fiber also helps regulate blood sugar and insulin. The combination of high blood pressure, high blood sugar, insulin resistance, abdominal obesity, high triglycerides and low HDL cholesterol–is a frequent precursor of type 2 diabetes and has been linked to a low-fiber diet. Adding fiber to the diet protects against both the metabolic syndrome and diabetes.
The American Diabetes Association recommends that persons with type 2 diabetes get at least 25 grams of fiber a day. Some specialists suggest doubling that amount.
If you’ve ever tried to lose weight by cutting carbohydrates, you probably know something about the role of fiber. The cereal label that proclaims “9 grams net carbs” derives that figure by subtracting 5 grams of fiber from 14 grams of total carbohydrates per serving.
In more traditional terms, such foods are usually good choices because they offer complex, nutritionally dense carbohydrates as opposed to the simple carbohydrates of white bread, sweets or most processed foods.
A Harvard study that followed male and female subjects for 10 years found that those who ate high-fiber breads were less likely to have a heart attack than those who preferred bagels or baguettes. A more recent study concluded that it’s possible to lower your risk of heart disease by as much as 20 percent simply by switching from white to whole wheat bread.
The refining process which produces white flour involves removing the bran on the outside and the germ at the very center of the grain, leaving only the starchy endosperm that is in between. A slice of white bread has about one-eighth the fiber and considerably fewer vitamins and minerals than a slice of whole grain bread.
Seek Variety of Sources
Dietitians recommend getting fiber from a variety of sources, with ample quantities of the two types–soluble and insoluble fiber. They also recommend that you increase the fiber in your diet gradually, about 5 grams per day for a week at a time, to prevent intestinal unrest.
Soluble fiber, found in oat bran, is partially dissolved in water and can be fermented by bacteria in the large intestine. Other sources of soluble fiber include flaxseed, barley, beans, nuts and the pulp of fruit.
Soluble fiber slows digestion and absorption and has been shown to reduce cholesterol. In fact, one recent study of persons taking statin medications found that adding three to four grams of soluble fiber–the equivalent of a large serving of oatmeal–was as effective in lowering LDL cholesterol as doubling the dose of the cholesterol-lowering medication.
Other studies have demonstrated the beneficial effect of soluble fiber on both type 1 and type 2 diabetes, regulating blood sugar and aiding in weight loss.
Insoluble fiber, found in wheat bran, apple peel and most garden vegetables, does not dissolve and is not readily fermented. This is the type of fiber referred to as roughage or bulk. It speeds the passage of waste through the intestines, keeping the bowels regular and lowering the risk of diverticular disease and perhaps colon cancer.
The quick passage through the bowels reduces exposure to toxic, cancer-causing substances, and several studies in the past concluded that dietary fiber reduced the risk of colorectal cancer. This view was later challenged by the results of some large, well publicized studies which found only a weak correlation between dietary fiber and either colon cancer or pre-cancerous polyps. Even more recently, two trials, including the EPIC study involving about 500,000 adults, found that a doubling of total fiber intake could lead to a 40 percent reduction in colorectal cancer risk.
Whatever its role may be in preventing colon cancer, fiber has plenty to recommend it. Whether it’s a bowl of oatmeal in the morning, a sandwich made with whole wheat bread or a bowl of black bean soup, fiber is there in ample quantities, giving you flavor, a satisfying texture...and numerous health benefits.
Michelle Herbert, PharmD, CDE
