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Fiber for preventing heart disease
If we were to sit down and have a "heart to heart," I would tell you that one of the best things that you could do on your own to protect your heart is to follow a high-fiber diet. Numerous studies have produced compelling evidence to support this. 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% lower risk of coronary heart disease, compared to a low-fiber intake. Another study of over 31,000 California Seventh-day Adventists found a 44% reduced risk of nonfatal coronary heart disease and an 11% reduced risk of fatal coronary heart disease for those who ate whole wheat bread compared with those who ate white bread. One minor change in their diets provided a protective effect that could save their lives.
Another strong predictor of heart disease is abnormal blood cholesterol, LDL, and/or HDL levels. It appears that soluble fiber reduces the absorption of cholesterol in your intestines by binding with bile (which contains cholesterol) and dietary cholesterol so that the body excretes it. The oat bran and bean fiber intervention trials where dietary fiber supplementation was combined with a low-fat diet shows that reductions in total cholesterol levels ranged from 8-26%. Other studies have shown that 5 to 10 grams of soluble fiber a day decreases LDL cholesterol by about 5%. All of these benefits will occur regardless of changes in dietary fat. In a trial with low fat and low fat plus high fiber groups, the group consuming high fiber exhibited a greater average reduction (13%) in total cholesterol concentration than the low fat (9%) and the usual diet (7%) groups. It seems that you don't have to change everything to gain something.
Fiber for bowel disorders
"Roughing" up your diet can be the key to healthier bowels. With the introduction of white flour came an increased prevalence of bowel disorders such as diverticulosis, diverticulitis, hemorrhoids, polyps, colon cancer, and irritable bowel syndrome (IBS). In Burkitt's early research into this phenomenon, he made reference to the fact that the typical African stool specimen was large and soft, and that stool transit times were rapid, compared to the puny hard fecal deposits and slow transit times of Europeans. In one of his studies, they conducted elaborate experiments in which volunteers in England, India, and Africa had their bowel movements timed and their stools weighed. Among the results of the study: People living under primitive conditions, on diets high in insoluble fibers, passed from 2½ to 4½ times as much feces as sailors in the Royal Navy, and were relatively free of many of the diseases studied. Current research supports the early findings. Studies have shown that a high-fiber diet (particularly fruit and vegetable fiber) help to prevent diverticulosis and will decrease the risk of complications if you have it. Although the mechanism by which fiber may be protective against diverticulosis is unknown, several hypotheses have been proposed.
For example, some scientists report that fiber helps by decreasing transit time, increasing stool weight, and decreasing pressure within the colon. The same has been found for irritable bowel syndrome (IBS). The current guidelines for the treatment of IBS include following a high fiber diet. The bulk that fiber provides is thought to help prevent the painful spasms often associated with IBS and aid in comfortable regularity. There is still a great deal of debate about the role of fiber in preventing colon cancer. The studies that look for connections with people's diets and their health have seen a trend in low-fiber diets and people with colon cancer. The studies that tried to intervene by putting people on high-fiber diets in order to prevent colon cancer or polyps did not find the same protective relationship. Burkitt's work and a more recent study showed that a daily stool weight greater than 150 grams needs to be achieved for the protective affect against colon cancer. This was not taken into account in many of the studies and may be the reason the protective effect was not found.