Fiber, a nutrient once associated with powder supplements aimed at older populations, is now making the rounds as one of the latest “It” nutrients, with food manufacturers adding it to everything from white bread to Froot Loops. Assumably, this is because consumers are becoming increasingly aware of fiber’s health benefits and are demanding it; however, most people have little idea what it actually does in the body.
When we understand how dietary fiber functions after we’ve eaten it, it starts to make sense that we can eat almost unlimited quantities of foods rich in fiber without gaining weight.
What is Fiber?
Found only in plant foods, fiber is a polysaccharide (carbohydrate) that cannot be digested and absorbed by humans. It comes in two forms: soluble (dissolves in water) and insoluble (cannot dissolve in water). Soluble fiber ferments in the large intestine before passing and therefore can contribute an insignificant number of calories to the diet; insoluble fiber passes through the digestive tract virtually unaltered. Soluble fiber is found in foods like fruits, vegetables, legumes, and some grains like oats and barley, while insoluble fiber is found in whole grains, nuts and seeds, and the skins of fruits and vegetables.
Dietary Fiber and Digestive Health
Perhaps the best known benefit of fiber consumption, fiber adds bulk, or roughage, to food and therefore is the nutrient responsible for pushing food swiftly through the digestive tract. Insoluble fiber plays more of a physical role, in that by moving food along it can help ease constipation and produce regular bowel movements.
Soluble fiber, on the other hand, plays more of a chemical role: as it ferments, it absorbs water, turning it into a gelatinous substance that traps sugars and slows the absorption of glucose, thus stabilizing blood sugar levels (more on this below). It also is known to balance pH levels in the intestines, which may reduce the risk of colon cancer.
Cardiovascular Benefits of Eating More Fiber
Consumption of soluble fiber has been linked to the lowering of LDL (“bad”) cholesterol levels. Simply put, soluble fiber slows absorption of cholesterol-raising fats (like saturated fats, trans fats, and dietary cholesterol) by moving it out of the body via the intestines. Because high cholesterol is the culprit in arterial blockage, keeping LDL and total cholesterol levels low is a smart strategy for warding off heart disease.
Additionally, because eating soluble fiber can help keep blood sugar levels down and therefore reduce insulin production (and subsequent insulin resistance), it has been linked to the prevention of diabetes and metabolic syndrome.
Eat Fiber to Lose Weight
A diet rich in fiber can aid in weight loss, whether directly or indirectly. First, foods rich in fiber tend to be high in water and low in calories, so eating foods like vegetables and legumes in place of refined carbohydrates or saturated fat is an excellent way to reduce overall calorie intake. Second, the bulk in these foods makes you feel full. Think of how your stomach feels after you’ve eaten a whole apple---you may have only consumed 60-80 calories, but there’s not much room in there for more.
Finally, because of the blood-sugar-reducing effects of fiber consumption, you’ll be less likely to experience blood-sugar spikes and lows, which cause you to crave more carbohydrates and overeat late in the day.
Foods Rich in Fiber
Here’s a list of foods rich in both kinds of fiber to help you meet your daily quota of 25 grams for women and 38 grams for men (according to the October 2008 issue of Cooking Light):
Sources of Soluble Fiber
- Beans like soybeans, black beans, and garbanzos
- Lentils like peas
- Grains like oats, oatmeal, barley, and rye
- Vegetables like broccoli, carrots, and potatoes
- Fruits like apples and pears
- Supplements from sources such as psyllium seed husk
Sources of Insoluble Fiber
- Grains like whole wheat flour and wheat bran
- Nuts like almonds
- Seeds like flaxseed
- Skins of fruits and vegetables like apples, tomatoes, zucchini, and potatoes
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