Gut transit and carbohydrate uptake

Classical assessments of nutritional adequacy rely on tables of supposed nutrient requirements for animals or for man on the one hand, and the ability of feedstuffs to provide them on the other.These are expressed in gross or overall digestibility terms and do not relate to differences in the rates of amounts of digestion occumng in different parts of the gut.Yet in the case of carbohydrates, these differences in the pattern of digestion are factors which have a considerable bearing on animal growth, or human metabolism, e.g. in the diabetic state.The aim of the present review is to consider the importance of interrelations between transit, digestion, fermentation and absorption of carbohydrates.Examples will be drawn from studies in man and related information from the pig which appears to digest, absorb and metabolize carbohydrates in a similar way to human beings.From a nutritional and physiological point of view carbohydrates exhibit great diversity.In general, man and most animals are able to hydrolyse starch thoroughly and to absorb sugars rapidly in the small intestine.However, a substantial part of dietary carbohydrate can be in the form of non-starch polysaccharide (NSP; equivalent to dietary fibre): this is not hydrolysed by amylase, but is fermented by the gut microflora to a degree depending on its physical and chemical structure.