High-fiber foods lead to improved markers of bowel health

The benefits of whole grain foods, as compared to refined grain foods, are vast. In particular, rye foods, when ingested in reasonable amounts have potential health benefits that have not been thoroughly studied. When compared to wheat, rye is a slightly better source of total dietary fiber (DF), is more commonly utilized in its whole-grain form, and, along with cellulose, contributes more mixed linked beta-glucans and arabinoxylan. The latter fiber types are of high interest as they are present in soluble and insoluble forms, and arabinoxylan is considered to be an optimal substrate for fermentative generation of short-chain fatty acids (SCFAs), particularly butyrate in the colon. Butyrate at high concentrations in the colon is thought to improve bowel health and lower cancer risks through several mechanisms.

Functional effects of rye foods that may prove beneficial to bowel health include increased fecal bulk, the binding and effective elimination of potentially toxic metabolites, promotion of desirable fermentative activity to SCFAs, and the release of protective components such as lignans.

A study was undertaken to examine the influence of <100 gram rye grain, an amount that is culturally acceptable in Australia and that might lead to clear changes in measures of bowel health function. Specifically, researchers looked at the effects of these amounts of whole-grain rye flour and fiber-matched whole-wheat flour and low-fiber (refined) wheat-flour foods on markers of bowel health and colon cancer risk and on postprandial glucose and insulin responses.

The subjects were male, aged 40 to 65 years. Twenty-eight subjects completed the study that included three interventions of 4-week duration each in a randomized crossover design. The intervention diets were high-fiber rye, high-fiber wheat, and low-fiber foods. The low-fiber diet provided 19 g/d of dietary fiber, including low-fiber test foods as 140 g white bread. The high-fiber wheat diet provided 32 g/d of dietary fiber, including wheat test foods as 140 g whole-meal bread, 40 g whole-meal wheat crisbread, and 50 g whole-wheat breakfast cereal. The high-fiber rye diet provided 32 g/d of dietary fiber as 140 g whole-grain rye bread, 40 g rye crisbread, and 50 g whole-rye breakfast cereal. The subjects were counseled by a dietitian regarding maintaining a moderately low-fiber background diet. The subjects visited the clinic on four occasions for investigative procedures with an additional three visits for further dietary assessment and dispensing of test foods. On each study visit, subjects were weighed and a fasting venous blood sample was obtained. Fecal, urine, and blood samples were collected at the end of each study period. The subjects were also required to record what they ate during the final 3 days of each 2-week period.

Endpoint measures were fecal weight, fecal pH, fecal SCFA concentrations, fecal bile acid concentrations, and fecal ammonia. Other endpoint measures were the fasting and 1-hour postprandial glucose and insulin responses to a test meal with 50 g available carbohydrate as high-fiber rye, high-fiber wheat or low fiber and the concentrations of plasma enterolactone and fecal beta-glucouronidase.

Both high-fiber rye and wheat foods increased fecal output by 33% to 36% (P = 0.004) and reduced fecal beta-glucouronidase activity by 29% (P = 0.027). Postprandial plasma insulin was decreased by 46% to 49% (P = 0.0001) and postprandial plasma glucose by 16% to 19% (P = 0.0005). Rye foods were found to be associated with significantly (P = 0.0001) increased plasma enterolactone (47% and 71%) and fecal butyrate (26% and 36%), relative to wheat and low-fiber options, respectively.

It appears that fiber from rye may be more effective than that from wheat in terms of overall improvement of the biomarkers studied of bowel health. However, it does appear that both high-fiber rye and wheat food consumption is beneficial in regards to several markers of bowel and metabolic health when compared to that of low-fiber foods.

http://www.findarticles.com/p/articles/mi_m0887/is_5_2


G. McIntosh, M. Noakes, P Royle, et al. Am J Clin Nutr;77:967-974 (April, 2003).
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