Mmmm, fiber! Maybe you"ve seen the television ads: a legion of short-sleeved, skinny-tied nutrition nerds circulating through the community with their cereal boxes, earnestly trying to get you excited about eating your fiber!

If your macronutrients had roles in a TV drama, protein would surely be the noble hero and fat the tempting villain, with carbohydrate as the complex, misunderstood protagonist, ever struggling to find balance. And then there would be fiber, the dorky sidekick, the essential second banana, the butt of the jokes.

Strictly speaking, fiber really isn"t much of a nutrient. Dietary fibers are strings of sugar molecules, but the links between the molecules can"t be broken down by our digestive enzymes, so these sugars pass through our bodies without being metabolized. It provides bulk, but few or no calories.

Because of this, fiber can be a great friend to people trying to lose weight or gradually make the change to healthier eating habits. A massive study by Tufts University showed that when people consciously chose to consume more fiber, they reduced their overall caloric intake by about 18 percent and hence, lost weight"even if they didn"t deliberately cut back on other foods.

The researchers said that"s probably because of specific characteristics of high-fiber foods. To begin with, high fiber foods like vegetables and whole grains are generally lower-calorie to begin with. They also take more time to chew, giving the body a better to chance to recognize that it"s been fed"before it"s been overfed!

And high-fiber foods stay in the stomach longer, and that keeps the feeling of fullness and satisfaction around, delaying the return of hunger and another round of eating.

There are a two kinds of fiber found in fruits, vegetables and grains"soluble and insoluble fiber.

Soluble fiber dissolves in water, forming a thick, jelly-like substance. Soluble fiber is longer lasting than insoluble fiber, so it stays in the stomach longer and helps to decrease hunger. It is also helps lower cholesterol, control blood sugar, decrease carbohydrate absorption, and bind to fat from our foods and pull it from our system.

Fruits that contain soluble fiber include apples, pears, oranges, grapefruit and figs. Among the vegetables containing soluble fiber are beets, okra, carrots, and dried beans. Oatmeal and legumes (dried beans, peas, and lentils) are other good sources. More exotic sources of soluble fiber are carob seeds and seaweed.

The thickening property of soluble fiber is apparent in the jams and jellies we eat. Pectin is a soluble fiber that comes from the pulp of soft fruits and some vegetables; it is the stuff that makes jellies gel.

Soluble fiber changes very little as it passes through the body. Acting mainly as a sponge, it absorbs many times its weight in water. Fiber that has absorbed water adds bulk to the stool, which generally causes it to move through the intestines faster. Because of this, it may prevent diverticulosis and constipation.

Insoluble fiber is abundant in unrefined cereals, whole-grain flours, fruits and vegetables. Fruits that are rich sources of insoluble fiber include berries, prunes, bananas, cherries, plums, apples and pears. Vegetables containing insoluble fiber include cauliflower, onions, broccoli, mushrooms, spinach, potatoes, carrots and beans.

People are a little more aware of fiber today than they were in our parents" generation. It really wasn"t until about the 1960s that fiber began to come into its own as the essential companion to fats, protein and carbs.

British researchers working in Africa around that time noted that Africans had a much lower incidence of certain diseases, heart disease and diabetes in particular, compared to folks in western cultures. They figured the Africans" high-fiber diet had something to do with it, as most native Africans eat large quantities of unprocessed plant foods and very little fat or animal protein.

They were right. Since then, numerous controlled studies have borne that out, and scientists can track the relationship between higher fiber intake and reduced incidence of the same diseases in the U.S. population.