Metabolomics/Nutrition/Dietary fiber

Dietary Fiber
Eating the right amount of dietary fiber a day can help manage a person's weight as well as the prevention of obesity. According to the article written by Linda Buckner and Karen Schweitzer, "soluble and insoluble fibers make up the two basic categories of dietary fiber. Insoluble fibers – cellulose, cellulose and lining – are not soluble in water. Foods that contain insoluble fibers are wheat bran, whole grain products and vegetables. Insoluble fibers are responsible for increased stool bulk and help to regulate bowel movements." With that said, fibers can do great progression for the human body. However, eating too much fiber can cause a strain on the human body therefore it is important to watch the intake of fiber. There are many side effects that can be caused by consuming too much fiber such as an unbalanced diet, or inadequate liquids that can result to pain. The best way to see if fiber is meeting needs, going to see a nutritionist is recommended. Everyone's needs are different based on their age, sex and activity level. A great resource to visit is www.mypyramid.gov, this gives an insight on what foods will help provide a balanced diet such as fruits, vegetables and grains.

Introduction
Fiber refers to carbohydrates that can't be digested. it is present in all plants that are eaten for food, (fruits, begetables, grains, and legumes.)There are a number of ways to categorize fiber. One way is from its source of origin, for example, fiber from grains is referred to cereal fiber. Another way is how easily the fiber dissolves in water. Soluble fiber partially dissolves, and insoluble fiver does not dissolve.

Currently its recommended that children and adults consume at least 20 grams of dietary fiber per day from food. The more calories you eat each day, the more fiber you need; teens and men may require upwards of 30 to 35 grams per day or more. Unfortunately, the average American eats only 15 grams of dietary fiber a day.

Fiber appears to reduce the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation.

Fiber and Colon Cancer
For a long time, Americans have been told to consume a high-fiber diet to lower the risk of colon cancer—mainly on the basis of results from relatively small studies. More recently, larger and better-designed studies have largely failed to show a link between fiber and colon cancer. One example is 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).

Fiber and Heart Disease
In the United States, coronary heart disease is a leading cause of death for both men and women. This disease is characterized by a buildup of cholesterol-filled plaque in the coronary arteries which are the arteries that feed the heart. This causes them to become hard and narrow, a process referred to as atherosclerosis. Total blockage of a coronary artery produces a heart attack.

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. (3) 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, compared to a low fiber intake. (4) Cereal fiber, which is found in grains, seemed particularly beneficial. A related Harvard study of female nurses produced quite similar findings. (5)

Fiber intake has also been linked with the metabolic syndrome, a constellation of factors that increases the chances 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, the body's main fat-carrying particle, and low levels of HDL (good) cholesterol. Several studies suggest that higher intake of cereal fiber and whole grains may somehow ward off this increasingly common syndrome. (6,7)

Sources of Soluble & Insoluble Fiber
Soluble Fiber: Oatmeal, oatbran; Nuts and seeds; Legumes; Beans; Dried peas; Lentils; Apples; Pears; Strawberries; Blueberries Insoluble Fiber: Whole wheat bread; Barley; Couscous; Brown rice; Bulgur; Whole grain breakfast cereals; Wheat bran; Seeds; Carrots; Cucumbers; Zucchini; Celery; Tomatoes The Harvard studies of male health professionals and female nurses both found that 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 (8) and the European Prospective Investigation Into Cancer and Nutrition–Potsdam, have found similar results.

When it comes to factors that increase the risk of developing diabetes, a diet low in cereal fiber and rich in high-glycemic-index foods (which cause big spikes in blood sugar) seems particularly bad. Both Harvard studies—of nurses and of male health professionals—found that this sort 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. (9-11)

A recent meta-analysis of seven major studies showed that cardiovascular disease (heart attack, stroke, or the need for a procedure to bypass or open a clogged artery) was 21 percent less likely in people who ate 2.5 or more servings of whole grain foods a day compared with those who ate less than 2 servings a week. (12) Another meta-analysis of several large studies, including more than 700,000 men and women, found that eating an extra 2 servings of whole grains a day decreased the risk of type 2 diabetes by 21 percent. (13) So to protect against heart disease and diabetes, perhaps the best advice is to choose whole grain, high-fiber foods at most meals.

Fiber and water intake
The fiber in wheat bran and oat bran seems to be more effective than similar amounts of fiber from fruits and vegetables. Experts recommend increasing fiber intake gradually rather than suddenly. As fiber intake is increased, the intake of beverages should also be increased, since fiber absorbs water.

Recommendations for Fiber
Fiber is an important part of a healthy diet, and you should get a least 20 grams a day, more is better. The best sources are whole grain foods, fresh fruits and vegetables, legumes and nuts. Eat whole fruits instead of drinking fruit juices. Replace white rice, bread, and pasta with brown rice and whole grain products. Choose whole grain cereals for breakfast. Snack on raw vegetables instead of chips, crackers, or chocolate bars. Substitute legumes for meat two to three times per week in chili and soups.

dietary fiber and diabetes
A high dietary fiver intake is recommended by most diabetes and nutritional associations. "It is accepted that viscous and gel-forming properties of soluble DF inhibit macronutrient absorption, reduce postprandial glucose response, and beneficially influence certain blood lipids. Colonic fermentation of naturally available high fiber foods can also be mainly attributed to soluble DF, whereas no difference between soluble and insoluble DF consumption on the regulation of body weight has been observed. However, in prospective cohort studies, it is primarily insoluble cereal DF and whole grains, and not soluble DF, that is consistently associated with reduced diabetes risk, suggesting that further, unknown mechanisms are likely to be involved. Recent research indicates that DF consumption contributes to a number of unexpected metabolic effects independent from changes in body weight, which include improvement of insulin sensitivity, modulation of the secretion of certain gut hormones, and effects on various metabolic and inflammatory markers that are associated with the metabolic syndrome.

© 2008 American Society for Nutrition J. Nutr. 138:439-442, March 2008

Health benefits and practical aspects of high-fiber diets
Over the past 20 years dietary fiber has emerged as a leading dietary factor in the prevention and treatment of chronic diseases. High fiber intakes are associated with lower serum cholesterol concentrations, lower risk of coronary heart disease, reduced blood pressure, enhanced weight control, better glycemic control, reduced risk of certain forms of cancer, and improved gastrointestinal function. Dietary fiber can be categorized into water-soluble and water-insoluble components. Dried beans, oat products, and certain fruits and vegetables are good sources of soluble fiber. Most plant foods are good sources of insoluble fiber and wheat bran is a concentrated form of insoluble fiber. Current guidelines advise a doubling of dietary fiber intake for Americans. Inclusion of ample servings of fruits and vegetables, whole grains, and dried beans and peas will help individuals meet these guidelines.

http://www.ajcn.org/cgi/content/abstract/59/5/1242S

Insoluble fiber binds water, making stools softer and bulkier. Therefore, fiber, especially that found in whole grain products, is helpful in the treatment and prevention of constipation, hemorrhoids and diverticulosis. Diverticula are pouches of the intestinal wall that can become inflamed and painful. In the past, a low-fiber diet was prescribed for this condition. It is now known that a high-fiber diet gives better results once the inflammation has subsided. Low blood cholesterol levels (below 200 mg/dl.) have been associated with a reduced risk of coronary heart disease. The body eliminates cholesterol through the excretion of bile acids. Water-soluble fiber binds bile acids, suggesting that a high-fiber diet may result in an increased excretion of cholesterol. Some types of fiber, however, appear to have a greater effect than others. The fiber found in rolled oats is more effective in lowering blood cholesterol levels than the fiber found in wheat. Pectin has a similar effect in that it, too, can lower the amount of cholesterol in the blood.Other claims for fiber are less well founded. Dietary fiber may help reduce the risk of some cancers, especially colon cancer. This idea is based on information that insoluble fiber increases the rate at which wastes are removed from the body. This means the body may have less exposure to toxic substances produced during digestion. However, more recent studies have not confirmed the protective effects of fiber in developing colon cancer. A diet high in animal fat and protein also may play a role in the development of colon cancer.

High-fiber diets may be useful for people who wish to lose weight. Fiber itself has no calories, yet provides a "full" feeling because of its water-absorbing ability. For example, an apple is more filling than a half cup of apple juice that contains about the same calories. Foods high in fiber often require more chewing, so a person is unable to eat a large number of calories in a short amount of time.

http://www.ext.colostate.edu/pubs/foodnut/09333.html

Foods high in dietary fiber
Soluble: beans, oat bran, fruits, and vegetables. Insoluble: whole grains, vegetables and beans.

Dietary fiber is found only in plant foods: fruits, vegetables, nuts and grains. Meat, milk and eggs do not contain fiber. The form of food may or may not affect its fiber content. Canned and frozen fruits and vegetables contain just as much fiber as raw ones. Other types of processing, though, may reduce fiber content. Drying and crushing, for example, destroy the water-holding qualities of fiber.

The removal of seeds, peels or hulls also reduces fiber content. Whole tomatoes have more fiber than peeled tomatoes, which have more than tomato juice. Likewise, whole wheat bread contains more fiber than white bread. Table 2 lists the dietary fiber content of some common foods.

http://www.ext.colostate.edu/pubs/foodnut/09333.html