49 Influence of oat β-glucan on postprandial glycemic and insulinemic responses to a meal or oral sugar

Abstract

s / Journal of Equine Veterinary Science 35 (2015) 400e417 405 49 Influence of oat b-glucan on postprandial glycemic and insulinemic responses to a meal or oral sugar J. Weir*, V. Robbins, J.M. Bobel, L.A. Skurupey, and L.K. Warren University of Florida, Gainesville, FL, USA Oats are a favored cereal grain in equine rations and are rich in b-glucan (BG). This soluble fiber has been linked to health benefits in humans, including lowered cholesterol and postprandial glucose and insulin. We hypothesized that oat BG would yield similar benefits in horses. Eight mature, clinically healthy Quarter Horses (mean ± SEM, 569 ± 2 kg) were used in a 4 X 4 Latin square design study to determine the effect of oat BG on glycemic and insulinemic responses. Horses were fed 4 diets differing in amount and source of BG for 22 d: cracked corn (low BG control), regular feed oats (moderate BG), a highBG oat variety (high BG), or corn top-dressed with a concentrated oat BG powder (high BG). Both high BG diets provided 170 mg BG/kg BW/d. All diets were isocaloric. Horses also had free access to pasture forage and were fed a vitamin/mineral supplement. In each of 4 periods, 2 horses were fed each diet. Blood samples were obtained on d 0 and 21 for determination of serum total cholesterol. On d 21, glycemic and insulinemic responses to the assigned treatment diet were evaluated after an 8-h fast. Meal size was standardized to provide 0.8 g NSC/kg BW (an amount equal to the habitual meal size for both oat diets, but a lowered meal size for diets containing corn). On d 22, glycemic and insulinemic responses to an oral dose of sugar (corn syrup, 0.15 mL/kg BW) were evaluated after an 8-h fast. At the completion of each 22-d period, horses underwent a 13-d dietary washout (corn control diet), followed by reallocation of treatments. Data were compared using mixed model ANOVA with repeated measures. Serum cholesterol was not affected by diet and averaged 75.2 ± 1.6 mg/dL. Time to consume the meal differed between diets (P < 0.0001), averaging 13.4 and 7.5 min for diets containing oats and corn, respectively. Insulin response to a meal was affected by diet (P < 0.0001), time (P < 0.0001) and diet time (P < 0.0001), where serum insulin was higher and remained elevated longer in response to meals containing oats (regular or high BG) compared with the 2 diets containing corn. In response to the oral sugar test, insulin was affected by time (P < 0.0001) and diet time (P 1⁄4 0.027), with a lower response in the 2 diets containing a high level of BG compared with the corn and regular oat diets. Diet did not affect glycemic responses to either the meal or the oral sugar test. Results of the meal test likely reflect differences in foregut starch availability between oats and corn. However, responses to the oral sugar test suggest that habituation to diets containing a high level of oat BG may reduce the magnitude of insulin response.