Inter-laboratory validation of the starch digestibility method for determination of rapidly digestible and slowly digestible starch.

The digestibility of starch in foods, which is influenced by the ingredients, formulation and preparation conditions, is a major determinant of glycaemic response. The terms rapidly digestible starch (RDS) and slowly digestible starch (SDS) along with the associated analytical methodology were developed by Englyst to characterise this nutritionally relevant food attribute. The measurement uncertainty of this starch digestibility method is evaluated here with an inter-laboratory trial.

Evaluation of methods of analysis for dietary fibre using real foods and model foods.

Rationale And Objectives: There are several rational and empirical methods for the measurement of dietary fibre and its components. A selection of these methods were evaluated by investigation of a range of real foods and model foods with added resistant starch (RS), non-starch polysaccharides (NSP) and resistant oligosaccharide (RO) ingredients.

Methods: A range of rational methods were applied in determining specific carbohydrate constituents: RS, NSP and RO, including fructans.

Resistant carbohydrates stimulate cell proliferation and crypt fission in wild-type mice and in the Apc(Min/+) mouse model of intestinal cancer, association with enhanced polyp development.

Fermentation of carbohydrates in the colon can stimulate cell proliferation and could thus be a cancer risk. The effects of resistant carbohydrates, i.e.

Nutritional characterization and measurement of dietary carbohydrates.

Dietary carbohydrate characterization should reflect relevant nutritional and functional attributes, and be measured as chemically identified components. A nutritional classification based on these principles is presented, with a main grouping into 'available carbohydrates', which are digested and absorbed in the small intestine providing carbohydrates for metabolism, and 'resistant carbohydrates', which resist digestion in the small intestine or are poorly absorbed/metabolized. For the available carbohydrates, the chemical division into the starch and total sugars categories does not adequately reflect the physiological or nutritional attributes of foods.

Carbohydrate bioavailability.

There is consensus that carbohydrate foods, in the form of fruit, vegetables and whole-grain products, are beneficial to health. However, there are strong indications that highly processed, fibre-depleted, and consequently rapidly digestible, energy-dense carbohydrate food products can lead to over-consumption and obesity-related diseases. Greater attention needs to be given to carbohydrate bioavailability, which is determined by the chemical identity and physical form of food.

Enhanced Escherichia coli adherence and invasion in Crohn's disease and colon cancer.

Background & Aims: Altered mucosal glycosylation in inflammatory bowel disease and colon cancer could affect mucosal bacterial adherence. This study aimed to quantify and characterize mucosa-associated and intramucosal bacteria, particularly Escherichia coli, in these conditions.

Methods: Mucosa-associated bacteria were isolated, after dithiothreitol mucolysis, from biopsy samples obtained at colonoscopy (Crohn's disease, n = 14 patients; ulcerative colitis, n = 21; noninflamed controls, n = 24) and at surgical resection (colon cancer, n = 21).

Degradation of cross-linked and non-cross-linked arabinoxylans by the intestinal microbiota in children.

In humans, nonstarch polysaccharides (NSP), such as arabinoxylans (AX), are not digested in the upper gut and provide fermentable carbon sources for bacteria growing in the large bowel. Despite the ubiquity of AX in nature, the microbiologic and physiologic consequences of AX digestion in the gut are poorly understood. In this study, we investigated the breakdown of ferulic acid-cross-linked AX (AXF) and non-cross-linked AX in children's intestinal microbiotas, using starch as a readily fermentable polysaccharide for comparative purposes.

The importance of dietary carbohydrates.

Forty years ago carbohydrates (CHO) were regarded as a simple energy source whereas they are now recognized as important food components. The human diet contains a wide range of CHO, the vast majority of which are of plant origin. Modern techniques based on chemical classification of dietary CHO replaced the traditional "by difference" measurement.

Glycaemic index of cereal products explained by their content of rapidly and slowly available glucose.

Elucidating the role of carbohydrate quality in human nutrition requires a greater understanding of how the physico-chemical characteristics of foods relate to their physiological properties. It was hypothesised that rapidly available glucose (RAG) and slowly available glucose (SAG), in vitro measures describing the rate of glucose release from foods, are the main determinants of glycaemic index (GI) and insulinaemic index (II) for cereal products. Twenty-three products (five breakfast cereals, six bakery products and crackers, and twelve biscuits) had their GI and II values determined, and were characterised by their fat, protein, starch and sugar contents, with the carbohydrate fraction further divided into total fructose, RAG, SAG and resistant starch.

Prebiotic digestion and fermentation.

Prebiotics, as currently conceived of, are all carbohydrates of relatively short chain length. To be effective they must reach the cecum. Present evidence concerning the 2 most studied prebiotics, fructooligosaccharides and inulin, is consistent with their resisting digestion by gastric acid and pancreatic enzymes in vivo.

Comparative effects of three resistant starch preparations on transit time and short-chain fatty acid production in rats.

A high-fiber diet may protect against colon cancer because of the butyrate generated in the colon by bacterial fermentation of nonstarch polysaccharides. Butryrate can reverse neoplastic changes, at least in vitro, and resistant starch (RS) represents a source of butyrate in vivo. We examined the effects of replacing normal maize starch in the diet of rats with three preparations of RS on the amounts of starch, butyrate, and other short-chain fatty acids in the cecum.

Functional food properties of non-digestible oligosaccharides: a consensus report from the ENDO project (DGXII AIRII-CT94-1095).

This paper results from the final phase of the ENDO project (DGXII AIRII-CT94-1095), a European Commission-funded project on non-digestible oligosaccharides (NDO). All participants in the programme met to perform a consensus exercise on the possible functional food properties of NDO. Topics studied during the project (including a workshop on probiotics and prebiotics) and related aspects, for which considerable evidence has been generated recently, were evaluated on the basis of existing published scientific evidence.

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 presented. The classification divides dietary carbohydrates into sugars, starch fractions, and nonstarch polysaccharides, and groups them into rapidly available glucose (RAG) and slowly available glucose (SAG) as to the amounts of glucose (from sugar and starch, including maltodextrins) likely to be available for rapid and slow absorption, respectively, in the human small intestine.

Objective: We hypothesize that RAG is an important food-related determinant of the glycemic response.

Dietary fiber and colorectal cancer risk.

We conducted a population-based case-control study among different ethnic groups in Hawaii to evaluate the role of various types and components of fiber, as well as micronutrients and foods of plant origin, on the risk of colorectal cancer. We administered personal interviews to 698 male and 494 female Japanese, Caucasian, Filipino, Hawaiian, and Chinese cases diagnosed during 1987-1991 with adenocarcinoma of the colon or rectum and to 1,192 population controls matched to cases by age, sex, and ethnicity. We used conditional logistic regression to estimate odds ratios, adjusted for caloric intake and other covariates.

Measurement of resistant starch in vitro and in vivo.

The digestibility of the starch in plant foods is highly variable, and is dependent on a number of factors, including the physical structure of both the starch and the food matrix. An in vitro technique has been developed to categorize starch in plant foods according to its likely rate and extent of digestion in the human small intestine. The in vitro method provides values for rapidly digestible starch, slowly digestible starch and resistant starch (RS).

Digestion and physiological properties of resistant starch in the human large bowel.

The digestion of four sources of resistant starch (RS) has been studied in twelve healthy volunteers who ate controlled diets for 15 d periods. RS from potato, banana, wheat and maize (17-30 g/d) was compared with a starch-free diet, a diet containing wheat starch that was fully digested in the small intestine, and with 18.4 g NSP from brand/d.

Measurement of rapidly available glucose (RAG) in plant foods: a potential in vitro predictor of the glycaemic response.

The glycaemic index (GI) is an in vivo measurement based on the glycaemic response to carbohydrate-containing foods, and allows foods to be ranked on the basis of the rate of digestion and absorption of the carbohydrates that they contain. GI values are normalized to a reference amount of available carbohydrate and do no reflect the amounts of carbohydrate normally present in foods; for example, a food with a low content of carbohydrates will have a high GI value if that carbohydrate is digested and absorbed rapidly in the human small intestine. This is potentially confusing for a person wishing to control his or her blood glucose levels by the choice of foods.

Ileal recovery of starch from whole diets containing resistant starch measured in vitro and fermentation of ileal effluent.

Six subjects with ileostomies consumed five diets containing 61-164 g starch/d of which 0.4-34.8 g was resistant starch (RS).

Dietary intakes of starch and non-starch polysaccharides in a west African village.

Dietary intakes of starch and non-starch polysaccharides (NSP) have been estimated for a rural West African community. These people eat directly from shared bowls of cooked food, and so measurement of any individual's food intake is not possible. Recently developed methodology for estimating food intake under these circumstances and the analysis of samples for dietary polysaccharides are combined to yield estimates of intakes of about 375 g starch and 25 g NSP/d for adult males, with lower intakes for women and children, related to their smaller body weights.

Gastrointestinal effects of food carbohydrate.

Dietary carbohydrate may be divided into monosaccharides and disaccharides (sugars), oligosaccharides [degree of polymerization (DP) 3-9], and polysaccharides (DP > 10). Their physiological properties and health benefits depend on the site, rate, and extent of their digestion or fermentation in the gut. Oligosaccharides are a diverse group of soluble carbohydrates, many of which are not digested by pancreatic enzymes.

Determination of the uronic acid constituents of non-starch polysaccharides by high-performance liquid chromatography with pulsed amperometric detection.

A technique is described for measurement of the uronic acid constituents of non-starch polysaccharides (NSP) by high-performance liquid chromatography with pulsed amperometric detection using two sets of hydrolysis conditions. In one set of hydrolysis conditions the uronic acid-containing polymers are hydrolysed by prolonged treatment with sulfuric acid only; in the other, the hydrolysate obtained in the Englyst procedure for the measurement of dietary fibre as NSP is buffered to between pH 3.5 and 4 and the uronic acid-containing polymers present are depolymerized enzymically.

Determination of dietary fibre as non-starch polysaccharides with gas-liquid chromatographic, high-performance liquid chromatographic or spectrophotometric measurement of constituent sugars.

Methods for the measurement of dietary fibre as non-starch polysaccharides (NSP) are described. A common enzymic removal of starch and acid hydrolysis of the NSP to their constituent sugars are followed by one of three alternative techniques, gas-liquid chromatography, high-performance liquid chromatography or spectrophotometry, for measurement of the released sugars. The results obtained by the three methods are in good agreement for a wide range of raw and processed foods.