Your mom was right about fiber being good for you-and not just because of its powers to aid digestion. A new analysis of nine years of data from the National Institutes of Health-AARP Diet and Health Study reports a link between dietary fiber and a reduced risk of death from cardiovascular, infectious and respiratory diseases, as well as a reduced risk of death from any cause. But not all types of fiber proved equally protective. Fiber from grains showed the strongest association with reduced mortality, while only a weak association was seen for fiber from beans and vegetables and none for fruit fiber. (For a complete guide to the different types and sources of dietary fiber, see our Special Report, The Facts on Fiber, in the February 2009 issue.)
This observation builds upon 35 to 40 years of research in which the definition of dietary fiber has been evolving, comments Tufts Irwin H. Rosenberg, MD, editor of the Health & Nutrition Letter. Fiber can be a mysterious term, however, so in any scientific investigation the type of fiber must be well-defined.
In the largest study of its kind to date, National Cancer Institute researchers led by Yikyung Park, ScD, compared fiber intake and deaths among 219,123 men and 168,999 women, ages 50 to 71. Participants completed a questionnaire asking how often they ate 124 different foods. They were then divided Fiber from Grains Linked to Living Longerinto five groups based on fiber intake, which ranged from a high of an average 29.4 grams per day for men and 25.8 grams for women to a low of 12.6 grams per day for men and 10.8 grams for women. Even those in the group consuming the most fiber barely met the current dietary-guidelines recommendations for women and fell well short for men (see box).
| How much fiber do you need? Dietary fiber is the non-digestible form of carbohydrates and lignin naturally found in plants. The 2010 Dietary Guidelines for Americans recommend 14 grams of fiber daily per 1,000 calories, or 25 grams per day for women and 38 grams per day for men. Most Americans fall far short of those goals, averaging only 15 grams daily. |
Over the next nine years, 20,126 of the men and 11,330 women died. Men and women in the highest-fiber group were 22% less likely to die of any cause than those in the bottom group. For every additional 10 grams of daily dietary fiber-the equivalent of four or five slices of whole-wheat bread-mortality risk dropped 12% for men and 15% for women.
The risk of cardiovascular, infectious and respiratory diseases was reduced by 24%-56% in men and 34%-59% in women with high fiber intakes. Men who ate more fiber were also at lower risk of death from cancer; a similar link was not seen in women, possibly because men are more likely to die from cancers of the esophagus and digestive system most affected by fiber intake.
Making fiber-rich food choices more often may provide significant health benefits, Park and colleagues concluded in the Archives of Internal Medicine. They noted that the findings aligned with previous research on the cardiovascular benefits of fiber, which may be due to effects on lipids, blood pressure, insulin factors and inflammation. The scientists cautioned that the findings on infectious and respiratory disease mortality, while interesting, require further investigation.
Researchers also conceded that they couldnt rule out the possibility that dietary fiber is simply a sign of an overall healthier lifestyle. Dr. Rosenberg adds, Thats always a concern, but no more so here than in other observational studies. It may also be that part of the benefit of dietary fiber comes from what other foods fiber displaces from the diet, such as less sugar or saturated fat. The latest dietary guidelines explicitly state that grains should take up a greater proportion of your plate.
TO LEARN MORE: Archives of Internal Medicine, online before print; abstract at dx.doi.org/10.1001/archinternmed.2011.18.