More Support for Dietary Fiber Reducing CV, All-Cause Death

February 15, 2011

February 15, 2011 (Rockville, Maryland)— Providing further support for the recommendation to eat plenty of dietary fiber, a new large prospective cohort study shows that fiber intake is associated with a significantly reduced risk of total death, including cardiovascular mortality and deaths from infectious and respiratory diseases [1].

In the study, which included 30 000 deaths over nine years of follow-up, subjects in the highest quintile for consumption of fiber were 22% less likely to die than those in the lowest quintile, Dr Yikung Park (National Cancer Institute, Rockville, MD) and colleagues report online February 14, 2011 in the Archives of Internal Medicine. "Prior studies have focused on the relationship between fiber intake and CVD, but few have examined the link between dietary fiber and mortality," Park told heartwire . "Our analysis adds to the literature and suggests dietary fiber intake is also associated with decreased likelihood of death." 

In an accompanying commentary [2], Drs Lawrence de Koning and Frank B Hu (Harvard School of Public Health, Boston, MA) say the "careful control for confounding" performed by Park et al "enhances the validity of these findings and supports the hypothesis that dietary fiber is important for longevity."

Park and colleagues agree: "The 2010 dietary guidelines for Americans recommend choosing fiber-rich fruits, vegetables, and whole grains frequently and consuming 14 g [of dietary fiber per] 1000 calories. A diet rich in dietary fiber from whole plant foods may provide significant health benefits," they say. (The 2011 dietary guidelines have just been released.)

Benefit Comes From Whole Grains

The researchers examined dietary-fiber intake in relation to mortality from specific causes in the National Institutes of Health (NIH)-AARP Diet and Health prospective cohort study. Diet was assessed at baseline using a food-frequency questionnaire, and cause of death was identified using the National Death Index Plus.

During an average of nine years follow-up, there were 20 126 deaths among men and 11 330 among women. Fiber intake was associated with a significantly lowered risk of total death among both sexes, with a multivariate-adjusted relative risk comparing the highest quintile of fiber consumption with the lowest of 0.78 (p<0.001) in both men and women. Eating fiber also lowered the risk of death from cardiovascular, infectious, and respiratory diseases by 24% to 56% in men and by 34% to 59% in women.

An inverse association between fiber intake and cancer death was observed in men, but not in women. Deaths from specific cancers were not presented, "which makes it difficult to evaluate the benefits of fiber on specific sites of cancer," say de Koning and Hu in their commentary.

And specifically, dietary fiber from grains, but not from other sources, was significantly inversely related to total and cause-specific death in both genders, they note, so "fiber isolates probably do not provide the same benefits as intact, whole grains," they observe.

Do Whole Grains Act to Reduce Inflammation? Further Research Needed

The editorialists add that the finding of a strong inverse association between fiber intake and cardiovascular death "supports decades of research indicating that dietary fiber protects against cardiovascular disease and its risk factors," including lowering blood pressure and reducing cholesterol.

Park and colleagues agree, noting that their findings for cardiovascular death are in agreement with several previous studies, including a pooled analysis in which the risk of CVD death fell by about 19% per 10-g/day increment of fiber intake.

But de Koning and Hu say that the "most striking finding" of the new study "is an inverse association between fiber intake and death from infectious and respiratory diseases"; this was "the strongest association observed by Park and colleagues, [who] suggest the benefit of dietary fiber is attributable to antioxidant and anti-inflammatory properties of whole-grain components," they note.

"The hypothesis that whole grains reduce disease severity and respiratory and infectious disease mortality via reduced inflammation is intriguing," they add, but "requires testing in randomized trials."

Park et al concur: "Further studies are needed to replicate our finding on the association between dietary fiber intake and risk of death from infectious and respiratory disease. And more studies are needed to understand the role of fiber in reducing inflammation and the mechanisms by which it protects against disease and risk of death," they conclude.

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