Bioavailability of Dietary Carbohydrates

Monday, February 18, 2013
Room 206 (Hynes Convention Center)
Klaus Englyst , Englyst Carbohydrates Ltd., Southampton, United Kingdom
Carbohydrates typically represent the largest single contributor to energy, which is derived either directly through the metabolism of the available carbohydrates absorbed in the small intestine, or from the resistant carbohydrates fermented in the colon. Metabolic responses to, and energy derived from, carbohydrates is influenced greatly by the ingredients used and how the product has been processed. This presentation will discuss how in conjunction with in vivo studies dietary carbohydrates have been characterized analytically to reflect their nutritional attributes.

Available starch can be described by the in vitro measures rapidly digestible starch and slowly digestible starch, shown to be important factors in determining glycaemic responses. The resistant starch term reflects the portion that, on average between individuals, escapes digestion in the small intestine, though this still provides some energy through fermentation. In its native state, starch tends to be slowly digested due to its occurrence as starch granules and its encapsulation within the grains or seeds. Disruption of the food matrix by grinding or milling and gelatinization of the starch through cooking can greatly increase the digestibility. This increases the energy available which was key to the advancement of early humans.  However, it can also result in a high proportion of rapidly digestible starch and the consequent raised glycaemic responses are potentially detrimental within the context of modern diets and our longer life spans.

There are various types of resistant carbohydrates, which for the naturally occurring diets consist mainly of non-starch polysaccharides from plant cell walls, and smaller amounts of resistant oligosaccharides present mostly in foods like onions, garlic and beans, and of resistant starch which is present in relatively small amounts in most processed foods.

The ability to characterize dietary carbohydrates in detail and taking into consideration their bioavailability attributes, such as the rate and extent of starch digestibility, provide tools with which to better understand the impact of diet on metabolism and health. This could assist in the development of improved processing techniques and products that are more consistent with the physiology that we have inherited as a species.