12.20.2013

by Todd Neale
Senior Staff Writer, MedPage Today

Eating more fiber-rich foods may provide protection against heart disease, a meta-analysis showed.
In pooled results from observational studies, an increase in total fiber intake of 7 grams per day was associated with reduced risks of both coronary heart disease (risk ratio [RR] 0.91, 95% CI 0.87-0.94) and cardiovascular disease (RR 0.91, 95% CI 0.88-0.94), according to Victoria Burley, PhD, of the University of Leeds in England, and colleagues.

The direction of the relationships was similar for all types of fiber, although some of the associations failed to reach statistical significance, the researchers reported online in BMJ.

“Because cardiovascular disease is one of the major causes of death in the U.K. and prevalence rates among the population are estimated to be around 13% to 16%, small reductions in risk could affect many thousands of individuals,” the researchers wrote, noting that increasing fiber intake by 7 grams per day is an achievable goal.
Such an increase “can be provided through eating just one portion of whole grains plus a portion of beans or lentils, or through two to four servings of fruit and vegetables,” they wrote.

They added, “Our findings relate only to fiber from food intake rather than from fiber isolates or extracts, and any public health messages must therefore reflect this.”
Numerous prior studies have examined the association between dietary fiber intake and risks of heart disease, with most showing an inverse relationship and some showing no relationship.

To explore the issue further, Burley and colleagues examined data from 22 observational studies with a minimum of 3 years of follow-up published since 1990. Most were conducted in the U.S. and Europe, although two were done in Japan and one was done in Australia.

In analyses broken down by fiber type and source, increased intake of insoluble fiber and fiber from cereals and vegetables was associated with reduced risks of both coronary and cardiovascular disease, and greater intake of fiber from fruits was associated with a lower risk of cardiovascular disease. Soluble fiber was not significantly associated with risks of either coronary or cardiovascular disease, although the risk ratios hinted at a benefit.

“The differing strengths of association by fiber type or source highlight the need for a better understanding of the mode of action of fiber components,” the authors wrote, noting that there were several potential mechanisms to explain the apparent benefit.

“Soluble, viscous fiber types can affect absorption from the small intestine because of the formation of gels that attenuate postprandial blood glucose and lipid rises. The formation of gels also slows gastric emptying, maintaining levels of satiety and contributing towards less weight gain,” they wrote. “Soluble fiber and resistant starch molecules are additionally fermented by bacteria in the large intestine, producing short-chain fatty acids, which help reduce circulating cholesterol levels.”

They said it is possible, however, that it is not the fiber itself that has the beneficial effects, but whole grains, because intake of fiber and whole grains is strongly associated.

They acknowledged some limitations of their study, including the potential for residual confounding in the included studies, the inability to prove causality, the use of dietary data from food frequency questionnaires — which may be limited when looking at individual nutrient intakes — and differences in the measurement of fiber intake among the studies.

“Despite these limitations, clinicians should enthusiastically and skillfully recommend that patients consume more dietary fiber,” according to Robert Baron, MD, of the University of California San Francisco.

“By systematically analyzing existing observational studies, [the] meta-analysis increases our confidence in the benefit — in terms of reduced cardiovascular disease and coronary heart disease events, of higher intakes of dietary fiber,” he wrote in an accompanying editorial.

From the American Heart Association:

• Implementing AHA Pediatric and Adult Nutrition Guidelines