February 18, 2011

More fiber intake associated with lower risk of death over nine year period

In an article published online in the American Medical Association journal Archives of Internal Medicine on February 14, 2011, National Cancer Institute researchers reveal the outcome of a study which found a lower risk of dying over a nine year average follow up period among men and women who consumed a high fiber diet.

Yikyung Park, ScD and associates evaluated data from 219,123 men and 168,999 women who were aged 50 to 71 upon enrollment in the National Institutes of Health-AARP Diet and Health Study. Demographic, lifestyle and other information was collected at the beginning of the study and dietary questionnaire responses were analyzed for fiber intake. Men's intake of fiber range from 13 to 29 grams per day, and women's from 11 to 26 grams daily.

Over a nine year average, there were 20,126 deaths among the men and 11,330 among the women enrolled in the study. Participants whose intake of fiber was among the top 20 percent of subjects at 29.4 grams per day for men and 25.8 grams for women had a 22 percent lower risk of dying than those who consumed the least amount, which was 12.6 grams for men and 10.8 grams for women. Subjects with the highest fiber intake had a lower risk of dying from cardiovascular, infectious and respiratory disease compared to the group with the lowest intake, however, fiber only appeared to be protective against cancer in men, a finding that the authors attribute to the difference between genders in the leading organ sites for cancer death. When fiber intake was analyzed according to its source, fiber from grain was associated with a reduction of death from all causes as well as cancer, cardiovascular disease and respiratory disease.

In their introduction to the article, Dr Park and colleagues note that fiber "has been hypothesized to lower the risk of coronary heart disease, diabetes, some cancers, obesity, and premature death because it is known to (1) improve laxation by increasing bulk and reducing transit time of feces through the bowel; (2) increase excretion of bile acid, estrogen, and fecal procarcinogens and carcinogens by binding to them; (3) lower serum cholesterol levels; (4) slow glucose absorption and improve insulin sensitivity; (5) lower blood pressure; (6) promote weight loss; (7) inhibit lipid peroxidation; and (8) have anti-inflammatory properties."

"The findings remained robust when we corrected for dietary intake measurement error using calibration study data; in fact, the association was even stronger with measurement error correction," they remarked. "The current Dietary Guidelines for Americans recommend choosing fiber-rich fruits, vegetables and whole grains frequently and consuming 14 grams per 1,000 calories of dietary fiber. A diet rich in dietary fiber from whole plant foods may provide significant health benefits."

Constipation

The average American eats only 10 to 15 grams (g) of fiber daily. Typical recommendations are 25 to 50 g of dietary fiber daily (Slavin JL 1987). Fiber is excellent for overall intestinal health and for alleviating chronic constipation. Although humans cannot digest fiber, the 5 pounds of friendly bacteria present in our digestive tract use fiber for fermentation and production of useful short-chain fatty acids that the cells of the intestine use for energy.

Most foods contain a mixture of soluble and insoluble fiber. Both are important in treating constipation. Soluble fiber is contained in oats, apples, lentils, barley, breads, and cereals. It is able to mix evenly with water, forming a soft gel. Insoluble fiber is contained in raw wheat bran, other whole grains, and fruits and vegetables. It mixes unevenly with water, forming a soft pulp. Your body does not absorb soluble or insoluble fiber during digestion. Fiber contributes volume to the stool mass, making it easier for the colon to push and propel larger and softer stools out of the body. Insoluble fiber encourages contraction of the colon.

Both fiber types contribute volume to individual stool masses. A larger mass of stool is easier for the colon to push against and propel, so larger, softer stools are easier to move and pass.

Glucomannan is a water-soluble dietary fiber derived from the konjac root (Amorphophallus konjac). Glucomannan is considered a bulk-forming laxative that promotes a larger, bulkier stool (Marsicano LJ et al 1995). Glucomannan generally helps produce a bowel movement within 12 to 24 hours.

Psyllium is a bulk-forming laxative that is high in fiber. Psyllium seeds contain 10 to 30 percent mucilage. The laxative properties of psyllium are caused by the swelling of the husk when it comes in contact with water. This forms a gelatinous mass and keeps the feces hydrated and soft. The resulting bulk stimulates a reflex contraction of the walls of the bowel and causes them to empty (McRorie JW et al 1998). Studies have shown that psyllium fiber is more effective than lactulose and other laxatives, and causes more frequent and bulkier bowel movements. It has also been documented to incur a lower incidence of adverse effects (Klaschik E et al 2003; McRorie JW et al 1998).

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