A Novel Natural Tracer Method to Measure Complex Carbohydrate Metabolism

Isotope dilution technique utilizing the triple tracer method has enabled accurate estimation of carbohydrate turnover after a mixed meal containing the simple carbohydrate glucose, as the carbohydrate source. However, this limits translational applicability to everyday meals that typically contain complex carbohydrates. Hence, we devised a triple tracer method to measure postprandial complex carbohydrate turnover and prandial indices of insulin secretion and action and compared the parameters to those obtained after an isocaloric, simple carbohydrate containing mixed meal. We measured the natural enrichment of 13C polysaccharide in several commercially available grains and selected rice and sorghum since their 13C enrichments represented the largest differences from 13C polysaccharide enrichment of the average American meal. We studied nondiabetic volunteers after either rice (n=8) or sorghum (n=8) and glucose (n=16) containing mixed meal ingestion and modified the triple tracer technique to calculate carbohydrate turnover. All meals were matched for calories and macronutrient composition. Rates of meal glucose appearance, endogenous glucose production and glucose disappearance differed between complex and simple carbohydrate containing meals. Interestingly, there was significant improvement in insulin sensitivity and indices of β-cell responsivity with complex than simple carbohydrate containing mixed meal ingestion. We present a novel triple tracer approach to estimate postprandial turnover of complex carbohydrate containing mixed meals using the natural 13C abundance of polysaccharides contained in commercially available grains in healthy adults.