Know Your Macronutrients: Fiber
Fiber. Roughage. For some people, that conjures up images of a gritty dietary supplement drinks they have to gag down. But a daily diet rich in food-based fiber sources could help them avoid that icky beverage, along with all sorts of other problems!
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.
An ally to dieters
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 Tufts researchers attributed that to 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 little more time and a little better 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.
Not just muffins and cereal
So what are your dietary fiber options? There are a lot of choices besides the usual bran muffin and those breakfast cereals hawked by the nutrition nerds. Dietary fiber comes in all sorts of fruits, vegetables and grains, and it comes in two types—soluble and insoluble fiber.
Insoluble fiber is the stuff most people think of when they hear the term “roughage,” it’s those parts of plant matter that our digestive system can’t really break down, so they pass right through. Insoluble fiber is abundant in unrefined cereals, whole-grain flours, fruits and vegetables.
Soluble fiber dissolves in water, forming a thick, jelly-like substance. Soluble fiber lasts longer in the stomach than insoluble fiber, so it helps to keep your hunger at bay longer. Soluble fiber also changes very little as it passes through the body, acting mainly as a sponge and absorbing many times its weight in water.
Fruits that are rich sources of insoluble fiber include berries, prunes, bananas, cherries, plums, apples and pears. 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, though these don’t show up in the American diet much. Vegetables containing insoluble fiber include cauliflower, onions, broccoli, mushrooms, spinach, potatoes, carrots and beans.
There’s plenty of evidence now that a high-fiber diet can protect us against heart disease and strokes. Research findings show that people who eat significant amounts of soluble fiber have low levels of the type of bad cholesterol that’s associated with these conditions. Insoluble fiber, while beneficial in other ways, doesn’t have this effect.
But perhaps the most familiar and immediate health benefit of fiber is its usefulness as an aide to digestion. Fiber that has absorbed water adds bulk to the stool, which generally causes it to move through the intestines faster, helping to prevent constipation and diverticulitis, the painful intestinal condition caused by the inflammation of small pouches that form in weak bowel walls.
Not only does fiber speed up the journey of food through the intestines because of the bulk it adds, but people on high-fiber diets also have stronger colon muscles. These muscles push the food along more rapidly than do the weak colon muscles of people who eat mostly soft foods.
So while fiber itself is more of a mechanical helper than a nutrient, the fact is that a high-fiber diet is bound to be richer in essential nutrients and therefore better all around. If you eat enough fresh vegetables, whole grains and fruits to get the fiber you need, you’ll probably be getting enough of the other essential vitamins and minerals we get from those natural sources.
And while you can get those vitamins and nutrients—or for that matter, even fiber—from a nutritional supplement, there’s nothing like the real thing.