Comparative methodologies for measuring metabolizable energy of various types of resistant high amylose corn starch

Energy values of high amylose corn starches high in resistant starch (RS) were determined in vivo by two different methodologies. In one study, energy values were determined according to growth relative to glucose-based diets in rats fed diets containing RS(2), heat-treated RS(2) (RS(2)-HT), RS(3), and amylase predigested versions to isolate the RS component. Net metabolizable energy values ranged from 2.68 to 3.06 kcal/g for the RS starches, and 1.91-2.53 kcal/g for the amylase predigested versions. In a second study, rats were fed a diet containing RS(2)-HT and the metabolizable energy value was determined by bomb calorimetry. The metabolizable energy value was 2.80 kcal/g, consistent with Study 1. Thus, high amylose corn based RS ingredients and their amylase predigested equivalents have energy values approximately 65-78% and 47-62% of available starch (Atwater factor), respectively, according to the RS type (Garcia, T. A.; McCutcheon, K. L.; Francis, A. R.; Keenan, M. J.; O'Neil, C. E.; Martin, R. J.; Hegsted, M. The effects of resistant starch on gastrointestinal organs and fecal output in rats. FASEB J. 2003, 17, A335).