Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2005
Publication Date: 11/1/2005
Citation: Reeves, P.G., Leary, P.D., Gregoire, B.R., Finley, J.W., Lindlauf, J.E., Johnson, L.K. 2005. Selenium bioavailability from buckwheat bran in rats fed a modified AIN-93g Torula yeast-based diet. Journal of Nutrition. 135:2627-2633.
Interpretive Summary: Selenium (Se) is an essential nutrient for humans and animals. The Se RDA for adult humans is 55 µg/d; however, dietary amounts as high as 200 µg/d in the highly available form in yeast have been shown to reduce the incidence of certain cancers. Numerous natural foods contain high amounts of Se, but for the most part, it is not known whether this Se can be absorbed and used by the body. This experiment was conducted to determine whether Se could be absorbed efficiently from buckwheat bran, a high-protein, high-fiber component of the seeds. To do this, rats were made Se deficient, where their Se-dependent enzymes and the amount of Se in various organs were reduced. Then Se from buckwheat was fed to these Se-deficient rats and the enzyme reactions and Se concentrations in tissues were measured and compared with those in similar rats fed a highly available form of Se; in this case, sodium selenite or selenomethionine. Then we calculated the percent bioavailability of Se from buckwheat relative to that in the highly available form. Results showed that Se from buckwheat bran was absorbed from 40 to 90% as well as well as Se from selenite or selenomethionine, depending on which enzyme and organ concentrations of Se was used to make the comparisons. Although some factors measured indicated low bioavailability of Se from buckwheat bran, how well Se is absorbed could depend on how the bran is cooked, how well the bran is digested, and how the bran is blended with other foods in the diet. More work is needed to determine how these factors affect Se bioavailability from buckwheat bran and other foods.
Technical Abstract: Selenium (Se) is an essential nutrient for humans and animals. The Se RDA for adult humans is 55 µg/d; however, dietary amounts as high as 200 µg/d in the highly available form of selenomethionine in yeast have been shown to reduce the incidence of certain cancers. A number of natural foods contain relatively high amounts of Se, but for the most part, the availability of food Se for absorption and utilization is unknown. This experiment was conducted to determine the bioavailability of Se from a high-protein, high-fiber bran-isolate of buckwheat groats that contains Se. The method used was the ability of Se from buckwheat bran to regenerate Se-dependent enzyme activities and tissue Se concentrations in Se-deficient rats. The responses generated from buckwheat bran Se were compared to a standard response curve generated by feeding graded amounts of Se as sodium selenite (Na2SeO3; NaSe) or selenomethionine (SeMet) in a newly reformulated AIN-93G-Torula yeast diet with a more balanced nutrient composition than older diets of this nature. Relative bioavailability was determined by using the slope-ratio assay method for enzyme data, or the parallel lines assay method for tissue Se concentration data. Results showed that Se availability from buckwheat bran based on the regeneration of serum Se was 70 to 80% as much as NaSe or SeMet. However, when based on the regeneration of muscle Se buckwheat bran was 90% as much as NaSe, but only 60% as much as SeMet. When using the regenerating ability of dietary Se on whole blood and liver glutathione peroxidase activity, buckwheat bran Se was 75 to 80% as much as NaSe or SeMet. However, for the regeneration of liver thioredoxin reductase, buckwheat bran Se was only 40% as much as NaSe and 70% as much as SeMet. The relative bioavailability of Se from buckwheat bran with all parameters considered was about 73% whether measured against NaSe or SeMet. Although some parameters indicated low bioavailability of Se from buckwheat bran, other factors such as Se speciation in the bran, digestibility of the bran, the cooking process, and combinations with other foods in the diet should be considered and analyzed before firm conclusions can be reached.