Rapidly available glucose in foods: an in vitro measurement that reflects the glycemic response

Background: A chemically based classification of dietary carbohydrates that takes into account the likely site, rate, and extent of digestion is prese nted. The classification divides dietary carbohydrates into sugars, starch fractions, and nonstarch polysaccharides, and groups them into rapidly avai lable glucose (RAG) and slowly available glucose (SAG) as to the amounts of glucose (from sugar and starch, including maltodextrins) likely to be avai lable for rapid and slow absorption, respectively, in the human small intes tine. Objective: We hypothesize that RAG is an important food-related determinant of the glycemic response. Design: The measurement of RAG, SAG, and starch fractions by an in vitro te chnique is described, based on the measurement by HPLC of the glucose relea sed from a test food during timed incubation with digestive enzymes under s tandardized conditions. Eight healthy adult subjects consumed 8 separate te st meals ranging in RAG content from 11 to 49 g. Results: The correlation between glycemic response and RAG was highly signi ficant (P < 0.0001) and a given percentage increase in RAG was associated w ith the same percentage increase in glycemic response. After subject variat ion was accounted for, RAG explained 70% of the remaining variance in glyce mic response. Conclusions: We show the significance of in vitro measurements of RAG in re lation to glycemic response in human studies. The simple in vitro measureme nt of RAG and SAG is of physiologic relevance and could serve as a tool for investigating the importance of the amount, type, and form of dietary carb ohydrates for health.