Fiber is something the body needs but never actually digests—in fact, it remains more or less the same from plate to toilet. It comes in two varieties, soluble and insoluble, and most plant-based foods contain a mixture of the two. Soluble fiber turns to gel in the stomach and slows digestion, which helps lower cholesterol and blood glucose. Insoluble fiber, on the other hand, remains unchanged all the way to the colon, making waste heavier and softer so it can shimmy through the intestines more easily. Regardless of these differences, neither type of fiber is ever absorbed into the body.
The modern western diet has left Americans with a serious nutrient deficiency, fiber. It is estimated that less than 5 percent of Americans get the recommended amount of dietary fiber each day. High fiber foods help to guard against cancer, heart disease, diverticulosis, kidney stones, PMS, obesity, and help to support a healthy digestive tract. Fiber is much more than just a regulator.
1. Corn
We're most familiar with the sunny, yellow version, but corn comes in a rainbow of colors—from pink to blue to black—each with its own special combination of antioxidant nutrients.
A single ear of corn, which is about a half cup of corn kernels, contains 2 grams of fiber. Popcorn is also a terrific—and low-calorie—fiber source, with about 3.5 grams of fiber per three-cup serving.
2. White beans
In addition to being rich in fiber, protein, and iron, white beans are one of the best nutritional sources of potassium—1 cup will cover 25% of your daily requirement for this hypertension-fighting nutrient.
Beans get a bad rap when it comes to gas, but the key is to amp up your fiber intake gradually, Brown says. "If you only eat (low-fiber) foods right now, don't suddenly switch to eating 40 grams of fiber a day, because that will cause a lot of stress to the digestive system."
3. Black beans
Black beans contain 15 grams of fiber per cup, and about 15 grams of protein. Their dark, rich color signals a high content of flavonoids, plant pigments that are powerful antioxidants. As you add beans and other high-fiber foods to your diet, be sure to drink more water, too, Brown says.
4. Kidney beans
The key ingredient in red beans and rice, kidney beans are popular in northern India as well as New Orleans. Like their cousins—pretty much all of the beans we eat share the Latin name Phaseolus vulgaris, or "common bean"—they're rich in fiber, protein, and iron.
5. Avocado
The creamy flesh of the avocado is a great fiber source; a two-tablespoon serving of avocado has about 2 grams of fiber and an entire fruit contains around 10 grams. Avocados are also an excellent source of mono- and polyunsaturated fats—the "good" kind that can help lower cholesterol and reduce heart-disease risk.
6. Brown rice
If you've been strictly a white-rice eater, the chewier texture and nuttier taste of brown rice can take some getting used to—but it's worth the effort. Every cup contains 3.5 grams of fiber.
Harvard researchers recently found that although eating five or more servings of white rice a week increased type 2 diabetes risk by 17%, adding a couple servings of brown rice per week decreased risk by 11%.
7. Edamame
Long popular in East Asian cuisine, edamame are immature soybeans boiled in the pod. You can pop them out of the pod into your mouth, or mix them into a tasty dip. A half-cup serving of edamame can contain up to 11 grams of protein and 9 grams of fiber, depending on the brand.
8. Pear
As with most fruits with edible skins, pears are most nutritious and fiber-rich when their skins are left intact. "Keeping the skin on is really important for fiber," Brown says. A medium-size unpeeled pear contains about 5.5 grams of fiber.
9. Oatmeal
Oats contain beta-glucan, a special type of fiber that has particularly powerful cholesterol-lowering effects, and may also boost immune-system function.
Oats also feature a good mix of soluble fiber (the type that lowers blood cholesterol) and insoluble fiber (which helps keep your digestion running smoothly).
10. Raspberries
Whether they're ruby-red or blue-black, raspberries are nutrition superstars. In addition to being extra-rich in fiber, one cup will give you about a third of your daily fiber needs—they're also chock-full of powerful antioxidants.
When raspberries aren't in season, buying them frozen is easier on your wallet.