Everything you need to know about fiber

diet, fiber, fruits, grains, heart disease, nuts, vegetables

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A vital nutrient we’ve all heard a lot about is fiber. But what is it, exactly, and why is it so important for your health? Dietary fiber is the indigestible parts of fruits, vegetables, beans, nuts, whole grains, and other plant foods. Fiber is what gives celery its crunch, for instance. In your intestines, fiber absorbs water and helps move digestion along; it acts a bit like a broom to sweep out waste. Technically, fiber is a type of carbohydrate, but because it’s mostly indigestible, it passes through you and doesn’t raise your blood sugar.

The importance of fiber in the diet became clear in the 1970s when Dr. Denis Burkitt and his colleagues published studies on the importance of fiber, based on their work in Africa. Dr. Burkitt hypothesized that certain diseases, such as appendicitis, were more common in Western cultures in part because of lower fiber intake. He noted the impact fiber had on bowel movements and even went as far as to theorize that he could predict the number of hospital visits someone would have based on their type of bowel movements. As it turns out, the effects of fiber are far broader than even Dr. Burkitt suggested.

One of his assumptions about fiber—that it helps prevents colon cancer—is somewhat controversial. Some studies have shown a significant link between a low-fiber diet and colon cancer and also some other types of cancer. On the other hand, Harvard’s long-running Nurses’ Health Study followed eighty thousand female nurses for nearly two decades and found that fiber was not a significant factor in reducing the risk of colon cancer.

The fiber-cancer link may still be questionable, but there are many other proven reasons to make sure you get enough fiber from your diet. Three of the best reasons are that fiber has been shown to reduce the risk of weight gain, diabetes, and heart disease. Another Harvard study, the long-running Physicians’ Health Study, followed forty thousand men for 15 years and found that those with the highest fiber intake had a 40 percent lower risk of heart disease compared to those with the lowest fiber intake. Similar findings were detailed when comparing diets in regard to fiber and sugar intake and the risk of diabetes. A huge study that looked at death from all causes found that those with the highest fiber intake were 22 percent less likely to die over the course of the study than those with the lowest fiber intake.

People who take in more fiber are also better able to control their weight. This works for several reasons. Some research shows that fewer calories are absorbed by the body from high-fiber diets. In addition, a diet high in fiber makes you feel full more quickly and staves off hunger longer as the food takes more time to move through your system. Higher-fiber foods are also less energy dense, meaning they contain fewer calories for the same volume of food. For example, a slice of whole wheat bread has about 70 calories and 2 grams of fiber, while a slice of white bread has about 120 calories and only about 0.6 grams of fiber. Another simple factor may be that fiber foods simply take more chewing. They take longer to eat, which gives your body time to produce the hormones that tell you you’re full. Because foods with a lot of fiber take longer to digest, their glucose enters the bloodstream more slowly. This may help avoid insulin surges and let you produce and use insulin more efficiently. Whatever the reason, fiber definitely helps to control weight.

Higher fiber intake can also help lower cholesterol and blood pressure, and it may lower levels of an inflammatory marker called C-reactive protein (CRP). A high level of C-reactive protein in the body can be a sign that the body’s process of breakdown and repair has tilted in favor of breakdown. Many studies have shown that consistently high CRP levels are associated with a higher risk of inflammation and of developing heart disease. Increasing your fiber intake is therefore a simple and smart way to keep inflammation down.

So how much fiber do you need? The answer depends on your age and gender. In general, men age 50 or younger need 35 grams of fiber a day; women age 50 or younger need 25 grams a day. Over age 51, the daily requirement drops a bit; men need 30 grams and women need 20 grams daily. Technically, there are two types of fiber: soluble and insoluble fiber. Soluble fiber partially dissolves in water; insoluble fiber resists digestion and doesn’t dissolve in water. Both types are important, and both are beneficial, but you don’t really need to worry about which type of fiber you’re getting. Just aim to consume your daily total from a variety of sources. When you consider that the average American only gets around 15 grams of fiber every day, there is certainly room for improvement. Here are some simple suggestions to help you increase your fiber intake:

  • Eat whole grain bread and pasta instead of white bread and semolina pasta. A study of thirty-one thousand Californians in the Adventist Health Study 1 found that those who ate whole wheat bread were a whopping 44 percent less likely to develop coronary artery disease compared to those who ate white bread. This is in line with other studies that show a significant effect from whole grain fiber. Swapping processed white flour for whole grains is a simple dietary change with a huge benefit.
  • Eat a higher fiber breakfast cereal. Look for one with at least 4 grams per serving and no added sugar. A lot of tasty choices qualify. You don’t have to eat Colon Blow, and it doesn’t have to taste like cardboard. Check the label for the fiber content and try some new brands. You may be pleasantly surprised.
  • Keep frozen berries handy. They’re great for tossing into smoothies and on top of cereal.
  • Eat more beans and nuts. Beans are easy to add to soups and stews; nuts can be tossed onto a salad and make a great snack.
  • It goes without saying that a good way to add fiber is to add fruits and vegetables, particularly if you eat the peel whenever possible. What’s more convenient and tasty than a crispy apple or juicy peach for a snack or dessert? Or some apple slices with a little bit of peanut butter? What about blending in a banana with a smoothie or dipping one into some cocoa powder for a snack? Perhaps add some bell pepper slices, zucchini chunks, or onion onto a grill skewer. Bake a sweet potato instead of a white potato. Keeping cut-up veggies such as carrot sticks in the refrigerator makes it easy to have a fiber-rich snack. Adding veggies to pasta sauce boosts the fiber and adds flavor as well. If you don’t feel like munching on these for a snack, think about some popcorn instead.

Adding high-fiber foods to your diet has another valuable benefit: all of those fruits, vegetables, nuts, and so on are rich in other nutrients beyond fiber. You’ll be boosting your intake of vital nutrients as you boost your fiber.

Increasing your fiber intake isn’t difficult. Find the high-fiber foods that fit your tastes and lifestyle, and make it a priority to eat more of them. Increase your fiber intake slowly over a period of a few weeks. This will give your digestive system time to adjust and avoid problems such as bloating, gas, and diarrhea from adding too much fiber too quickly. Take a look at the table below to get a general idea of the fiber content in some common foods.


Fiber Content of Common Foods

Food                                   Amount                                   Total Fiber Grams

Pinto beans                         1/2 cup                                                 7.4

Almonds                             1/2 cup                                                 6.4

Peanuts                               1/2 cup                                                 6.1

Kidney beans                      1/2 cup                                                 5.7

Prunes                                 1/2 cup                                                 5.7

Green peas                          1/2 cup                                                 4.4

Apple, with skin                1 medium                                              4.4

Sweet potato                      1 medium                                              4.0

Blueberries                          1 cup                                                    4.0

Oatmeal                              1 cup, cooked                                       4.0

Blackberries                        1/2 cup                                                 3.6

Popcorn                              3 cups, air popped                               3.5

Banana                                1 medium                                              3.1

Baked potato with skin      1 medium                                              2.9

Broccoli                              1/2 cup                                                 2.8

Grapefruit                           1 medium                                              2.9

Kale                                    1 cup, cooked                                       2.6

Carrots                                1/2 cup                                                 2.6

Corn                                    1/2 cup                                                 2.0

Whole wheat bread             1 slice                                                   2.0

Strawberries                        1/2 cup                                                 1.7

Tomato                               1 medium                                              1.5

White bread                        1 slice                                                   0.6

Iceberg lettuce                     1/2 cup                                                 0.4


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