On average, Americans consume 15 g or less of dietary fiber per day, which is far less than the recommended daily amounts. According to The National Academy of Sciences’ Institute of Medicine, the current recommended daily intake levels are 38 g of fiber for men and 25 g for women under the age of 50. Although regularity is a well-known benefit of a fiber-rich diet, there are also many others, with decreased cancer risk, improved cholesterol levels, and weight management at the top of the list.
Fiber is commonly classified as soluble, which dissolves in water, or insoluble, which doesn’t dissolve.
- Soluble fiber. This type of fiber dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels. Soluble fiber is found in oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium.
- Insoluble fiber. This type of fiber promotes the movement of material through your digestive system and increases stool bulk, so it can be of benefit to those who struggle with constipation or irregular stools. Whole-wheat flour, wheat bran, nuts, beans and vegetables, such as cauliflower, green beans and potatoes, are good sources of insoluble fiber.
The amount of soluble and insoluble fiber varies in different plant foods. To receive the greatest health benefit, eat a wide variety of high-fiber foods.
Benefits of a high-fiber diet
A high-fiber diet:
- Normalizes bowel movements. Dietary fiber increases the weight and size of your stool and softens it. A bulky stool is easier to pass, decreasing your chance of constipation. If you have loose, watery stools, fiber may help to solidify the stool because it absorbs water and adds bulk to stool.
- Helps maintain bowel health. A high-fiber diet may lower your risk of developing hemorrhoids and small pouches in your colon (diverticular disease). Studies have also found that a high-fiber diet likely lowers the risk of colorectal cancer. Some fiber is fermented in the colon. Researchers are looking at how this may play a role in preventing diseases of the colon.
- Lowers cholesterol levels. Soluble fiber found in beans, oats, flaxseed and oat bran may help lower total blood cholesterol levels by lowering low-density lipoprotein, or “bad,” cholesterol levels. Studies also have shown that high-fiber foods may have other heart-health benefits, such as reducing blood pressure and inflammation.
- Helps control blood sugar levels. In people with diabetes, fiber — particularly soluble fiber — can slow the absorption of sugar and help improve blood sugar levels. A healthy diet that includes insoluble fiber may also reduce the risk of developing type 2 diabetes.
- Aids in achieving healthy weight. High-fiber foods tend to be more filling than low-fiber foods, so you’re likely to eat less and stay satisfied longer. And high-fiber foods tend to take longer to eat and to be less “energy dense,” which means they have fewer calories for the same volume of food.
- Helps you live longer. Studies suggest that increasing your dietary fiber intake — especially cereal fiber — is associated with a reduced risk of dying from cardiovascular disease and all cancers.
How much fiber do you need?
The Institute of Medicine, which provides science-based advice on matters of medicine and health, gives the following daily fiber recommendations for adults:
Fiber: Daily recommendations for adults
|Age 50 or younger||Age 51 or older|
|Men||38 grams||30 grams|
|Women||25 grams||21 grams|
|Institute of Medicine|
Your best fiber choices
If you aren’t getting enough fiber each day, you may need to boost your intake. Good choices include:
- Whole-grain products
- Beans, peas and other legumes
- Nuts and seeds
Refined or processed foods — such as canned fruits and vegetables, pulp-free juices, white breads and pastas, and non-whole-grain cereals — are lower in fiber. The grain-refining process removes the outer coat (bran) from the grain, which lowers its fiber content. Enriched foods have some of the B vitamins and iron added back after processing, but not the fiber.
Fiber supplements and fortified foods
Whole foods rather than fiber supplements are generally better. Fiber supplements — such as Metamucil, Citrucel and FiberCon — don’t provide the variety of fibers, vitamins, minerals and other beneficial nutrients that foods do.
Another way to get more fiber is to eat foods, such as cereal, granola bars, yogurt and ice cream, with fiber added. The added fiber usually is labeled as “inulin” or “chicory root.” Some people complain of gassiness after eating foods with added fiber.
However, some people may still need a fiber supplement if dietary changes aren’t sufficient or if they have certain medical conditions, such as constipation, diarrhea or irritable bowel syndrome. Check with your doctor before taking fiber supplements.
Tips for fitting in more fiber
Need ideas for adding more fiber to your meals and snacks? Try these suggestions:
- Jump-start your day. For breakfast choose a high-fiber breakfast cereal — 5 or more grams of fiber a serving. Opt for cereals with “whole grain,” “bran” or “fiber” in the name. Or add a few tablespoons of unprocessed wheat bran to your favorite cereal.
- Switch to whole grains. Consume at least half of all grains as whole grains. Look for breads that list whole wheat, whole-wheat flour or another whole grain as the first ingredient on the label and have at least 2 grams of dietary fiber a serving. Experiment with brown rice, wild rice, barley, whole-wheat pasta and bulgur wheat.
- Bulk up baked goods. Substitute whole-grain flour for half or all of the white flour when baking. Try adding crushed bran cereal, unprocessed wheat bran or uncooked oatmeal to muffins, cakes and cookies.
- Lean on legumes. Beans, peas and lentils are excellent sources of fiber. Add kidney beans to canned soup or a green salad. Or make nachos with refried black beans, lots of fresh veggies, whole-wheat tortilla chips and salsa.
- Eat more fruit and vegetables. Fruits and vegetables are rich in fiber, as well as vitamins and minerals. Try to eat five or more servings daily.
- Make snacks count. Fresh fruits, raw vegetables, low-fat popcorn and whole-grain crackers are all good choices. A handful of nuts or dried fruits also is a healthy, high-fiber snack — although be aware that nuts and dried fruits are high in calories.
High-fiber foods are good for your health. But adding too much fiber too quickly can promote intestinal gas, abdominal bloating and cramping. Increase fiber in your diet gradually over a few weeks. This allows the natural bacteria in your digestive system to adjust to the change.
Also, drink plenty of water. Fiber works best when it absorbs water, making your stool soft and bulky.
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Some tips for increasing fiber intake:
- Eat whole fruits instead of drinking fruit juices.
- Replace white rice, bread, and pasta with brown rice and whole grain products.
- For breakfast, choose cereals that have a whole grain as their first ingredient.
- Snack on raw vegetables instead of chips, crackers, or chocolate bars.
- Substitute beans or legumes for meat two to three times per week in chili and soups.
Fiber and disease
Fiber appears to reduce the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation. Despite these benefits, fiber probably has little, if any, effect on colon cancer risk.
High intake of dietary fiber has been linked to a lower risk of heart disease in a number of large studies that followed people for many years. (16) In a Harvard study of over 40,000 male health professionals, researchers found that a high total dietary fiber intake was linked to a 40 percent lower risk of coronary heart disease. (17) A related Harvard study of female nurses produced quite similar findings. (18)
Higher fiber intake has also been linked to a lower risk of metabolic syndrome, a combination of factors that increases the risk of developing heart disease and diabetes. These factors include high blood pressure, high insulin levels, excess weight (especially around the abdomen), high levels of triglycerides, and low levels of HDL (good) cholesterol. Several studies suggest that higher intake of fiber may offer protective benefits from this syndrome. (19,20)
Type 2 diabetes
Diets low in fiber and high in foods that cause sudden increases in blood sugar may increase the risk of developing type 2 Diabetes. Both Harvard studies—of female nurses and of male health professionals—found that this type of diet more than doubled the risk of type 2 diabetes when compared to a diet high in cereal fiber and low in high-glycemic-index foods. (21-23) A diet high in cereal fiber was linked to a lower risk of type 2 diabetes.
Other studies, such as the Black Women’s Health Study (24) and the European Prospective Investigation Into Cancer and Nutrition–Potsdam, have shown similar results.
Read about what you can do to help prevent type 2 diabetes.
Diverticulitis, an inflammation of the intestine, is one of the most common age-related disorders of the colon in Western society. Among male health professionals in a long-term follow-up study, eating dietary fiber, particularly insoluble fiber, was associated with about a 40 percent lower risk of diverticular disease. (25)
Fiber and constipation
Constipation is the most common gastrointestinal complaint in the United States, and consumption of fiber seems to relieve and prevent constipation.
The fiber in wheat bran and oat bran is considered more effective than fiber from fruits and vegetables. Experts recommend increasing fiber intake gradually rather than suddenly, and because fiber absorbs water, beverage intake should be increased as fiber intake increases.
Studies have largely failed to show a link between fiber and colon cancer. One of these—a Harvard study that followed over 80,000 female nurses for 16 years—found that dietary fiber was not strongly associated with a reduced risk for either colon cancer or polyps (a precursor to colon cancer). (26)
Click Harvard School of Public Health for the original article.