The Health Benefits of a High Fiber Diet
The following is a discussion of the benefits of a high fiber diet.
Fiber refers to a group of substances that include plant polysaccharides and lignin that are resistant to the digestive enzymes. They consist of the structural components of plant cell walls, primarily cellulose, hemicellulose pectins and lignin. Cellulose is the main structural component of plant cell walls, hemicellulose consists of polymers of nonglucose sugars and lignan is a non-carbohydrate cell wall material that is highly resistant to degradation. Some fiber does undergo degradation by bacteria in the colon (large intestine).
Well, so much for the scientific description and big words!
Essentially, fiber is a complex carbohydrate and the part of the plant that cannot be digested.
Fiber can be either water soluble or water insoluble. Soluble fiber, which includes vegetable fiber, gums and pectins, lowers cholesterol and helps manage blood glucose (see below). Fruits, vegetables, dried beans and peas, nuts, seeds, brown rice, oat bran, barley bran and rice bran are prime sources.
Water-insoluble fiber such as wheat bran is less subject to digestion in the colon than are the water-soluble fibers. Insoluble fiber helps mainly with intestinal disorders such as Irritable Bowel Syndrome and Diverticulitis. It also shortens the time food is in the bowels and promotes more frequent bowel movements. Sources include wheat and corn bran, whole grain breads, cereals, vegetables, fruit skins and nuts.
A high fiber diet affects most segments of the digestive system. It increases the chewing time, which results in increased salivary and gastric juice flow. This subsequently decreases dental plaques and decay, satisfies the appetite more quickly and as a result reduces calory intake (a high fiber diet is a natural way to feel full sooner which can lead to weight loss).
The rate at which your stomach emptys and the rates of digestion and absorption are also affected by a high fiber diet. Guar gum and pectins increase the viscosity (thickness) of the partially digested food and decrease stomach emptying, although particulate fibers such as wheat bran promote more rapid stomach emptying.
Soluble fibers also have a cholesterol lowering effect. It increases the removal of bile acids, decreases intestinal absorption of fatty acids and cholesterol and decreases cholesterol synthesis. Soluble fiber also binds cholesterol for elimination.
Once in the colon, soluble fiber is fermented causing production of substances known as short chain fatty acids which are absorbed and cause further glucose and cholesterol control.
Recently, a study from Norway has demonstrated that a high fiber diet also decreases the tendency of the blood to clot, adding another mechanism for heart attack reduction
A high fiber diet improves diabetic control. Pectins, guar and beans appear to be the most effective in stabilizing blood glucose. The main action of fiber is in the gastrointestinal tract. Water-soluble fibers slow transit through the stomach and small intestine and are rapidly broken down by colonic bacteria. They do not alleviate constipation.
Water-insoluble fibers, on the other hand, are either slow or not fermented at all, and thus act as laxatives. Oats and psyllium seeds are exceptions. Oats contain 50 percent soluble fiber. Psyllium seed also acts as a soluble fiber. Both act as laxatives.
A high fiber diet appears to protect against colon cancer . A recent study in the New England Journal of Medicine disputed this beneficial effect of fiber, but there are a number of serious questions about this study, and much further study is needed. A review of 13 studies of colorectal cancer rates and dietary practices concluded there is substantial evidence that intake of fiber-rich foods reduces risks of both colon and rectal cancer.
It is estimated that the risk of colorectal cancer in the U.S. population could be reduced by almost 31 percent if fiber intake from food sources were increased an average of 13 grams/day.
On a molecular level, a recent study the mechanisms by which fiber protects against the formation of colon cancer. It has been shown that butyrate, the gas produced by the fermentation of fiber by bacteria in the colon, induces a protein formed within the cells that prevents the change of the normal colonic cell to a dysplastic (early cancerous) one. In other words, a high fiber diet clearly protects against the development of colon cancer.
A high fiber diet has also been shown to reduce the incidence of prostate cancer
A high fiber diet decreases the rate of diverticulitis and diverticulosis. Diverticuli are small herniations (cracks or holes) in the wall of the bowel that occur over the course of years due to the very high and sustained pressures generated within the colon. Diverticulosis refers to the presence of diverticuli within the colon.
These pressures within the bowel are needed for evacuation. They are much higher in a highly refined Western diet. In fact, diverticuli are unusual in certain parts of the world where diets are consistently high in fiber. Diverticulitis results when one of these diverticuli gets obstructed and ruptures. This can be life threatening and often requires surgery. Fiber creates more bulk and water content within the stool, which results in lower pressures being needed for evacuation.
A high fiber diet has many other beneficial effects. For example, a study in the Journal of the American Medical Association showed that fiber reduces the risk of heart attack in a way that was independent of cholesterol lowering, meaning that whether or not the cholesterol went down, the risk of heart attack was far lower if dietary fiber was increased by 10 grams per day.
It is recommended that dietary fiber intake for adults be in the range of 20-35 grams (g) per day. The average American consumes only 14 g of fiber per day, and most popular American foods are not high in fiber. The fiber-intake recommendation for children over the age of two is the age of the child plus five.
Clearly, North Americans need large increases in fiber to substantially improve overall health.
There is substantial evidence that lack of dietary fiber and nutrient deficiency are responsible for many of the diseases which afflict us.
Diabetes, heart disease, cancer, cataracts, and even aging itself can be prevented by proper nutrition.
The typical low fiber, high fat American diet is estimated to be responsible for 35% of all cancers.
Boston researchers reported in 1996 that increasing dietary fiber intake from the average 12 grams per day to 28 grams per day resulted in a dramatic 41% reduction in heart attacks .
The American Dietetic Association has advised all Americans to consume 25-35 grams of fiber each day. Guidelines have been developed for children by the American Academy of Pediatrics recommending that a child consume the number of grams of fiber equivalent to age plus 5-10 grams per day. Public health agencies are advocating the "optimal diet", that is, 25% of calories as fat and 25 grams of fiber per day .
At somewhere between 25 and 35 grams of fiber per day, people enter into a "health envelope" where there appears to be a reduction in the incidence of heart disease and certain cancers including colorectal, prostate and breast.
There are many mechanisms responsible for the dramatic health benefits of a high fiber diet.
Foods rich in soluble fiber include whole grain foods (made from oats, barley and oat bran), fruits, vegetables, legumes, brown rice and seeds. Foods high in insoluble fiber include whole grain foods (made from wheat, rice and corn) and some fruits and vegetables.
Because insoluble fiber keeps foods moving through the colon, it reduces the time that cancer-causing substances can remain in the digestive tract. Soluble fiber delays emptying of foods from the stomach resulting in a more uniform absorption of carbohydrates thereby improving glucose control. .
Dietary Fiber and Hypertension
A report recently published in the New England Journal of Medicine on the DASH Trial (Dietary Approaches to Stop Hypertension) compared the effects of three different diets on blood pressure in patients with hypertension. The first group followed the regular daily American low fiber, high fat diet (9 grams fiber, 37% fat). The second group followed a high fat, high fiber diet, (31 grams fiber, 37% fat). The third group followed a low fat, high fiber diet (31 grams fiber, 27% fat) that was supplemented with calcium (1240 mg) from low-fat dairy products. Sodium intake and body weights were maintained at constant levels.
A significant reduction was seen in both high fiber groups, however, the most profound reduction was seen in the low fat, high calcium, high fiber diet group. In that group the systolic and diastolic blood pressures fell by 11.4 and 5.5 mm Hg, respectively.
In summary, a high fiber diet, low in fat and high in dietary calcium is an effective alternative approach to the treatment of high blood pressure.
7-8 daily servings of grains and grain products 4-5 daily servings of vegetables 4-5 daily servings of fruit 2-3 daily servings of low-fat or non-fat dairy foods 1-2 daily servings of lean meat, poultry (no skin, breast preferable) or fish 4-5 weekly serving of legumes, nuts and seeds. Total daily fat intake not to exceed 30%
Foods high in dietary fiber also contain many potent anti-aging and disease preventing nutrients, cofactors, vitamins and antioxidants. The list is large.
Antioxidants appear to decrease the incidence of heart disease by preventing the oxidation of cholesterol making it less likely to get stuck in blood vessels .
Antioxidants also are believed to protect against a number of cancers and age-related chronic diseases such as macular degeneration, cataracts and skin photo aging. Phytochemicals, recently discovered compounds present in fruits and vegetables, prevent cancer by helping to remove cancer-causing substances from the cell or preventing entry into cells.
Reference: A Review of Fiber by Dr. Peter Gardner, M.D.
An information page on antioxidants is in the works and will be added shortly.
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