The glycaemic index (GI) is an in vivo measurement based on the glycaemicresponse 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 normalizedto a reference amount of available carbohydrate and do not 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 glucoselevels by the choice of foods. The rate and extent of starch digestion in vitro has been measured using a technique that classifies starch into three major fractions: rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). In addition, thistechnique gives a value for rapidly available glucose (RAG), which includes RDS, free glucose and the glucose moiety of sucrose. When the values for thirty-nine foods were expressed on the basis ofthe available carbohydrate content of these foods, highly significant (P<0·001) positive correlations were observed between GI and both RDS and RAG. The measurement of RAGin vitro provides values for direct calculation of the amount of glucose likely to be rapidly absorbed in the human small intestine and,thus, to influence blood glucose and insulin levels. These values can be used to compare foods, as eaten,on an equal-weight basis. Food-table RAG values would allow simple calculation of the total amount of RAG provided by single foods, by whole meals and by whole diets. Studies are planned in which RAG and the glycaemic response in man will be measured for identical food products.

Four pigs fitted with a gastric cannula were fed on a wheat-flour-based diet (WF) and three oat-based diets, consisting mainly of oat flour (OF), rolled oats (RO) or oat bran (OB), for 1 week each. The stomach contents were collected quantitatively daily at 0·5, 1, 2, 3 or 5 h after feeding. The viscosity (mPa. s) of the liquid fraction of stomach contents 1 h after feeding was 1·7 with diet WF, 15 with diet OF, 30 with diet RO and approximately 400 with diet OB. The viscosity and the concentration of β-glucan in the liquid phase was to some extent determined by the dietary level of β-glucan in the diet. However, there was a trend towards a lower viscosity after longer exposure to the gastric juices. The correlation between logarithmic values for viscosity and concentration of β-glucan in the liquid phase of digesta was r 0·45. On centrifugation of digesta there was a higher proportion present in the sediment phase when the pigs were fed on diets with a higher content of soluble dietary fibre (DF), suggesting that the digesta was more coherent. This possibility was supported by the higher water-holding capacity (WHC) of the sediment. Feeding diets with oats containing a higher soluble DF content led to lower recoveries of digesta, PEG 4000 (liquid-phase marker), and the DF components β-glucan and arabinoxylan in the first hour after feeding. No effect related to the DF content of the diet was seen in the gastric emptying of starch and Cr2O3 (solid-phase marker). In conclusion, soluble DF from oatsincreased the viscosity of stomach contents and increased the ability of the dry matter to retain water. Higher levels of soluble DF led to higher recoveries of digesta, the liquid phase and DF itself in the initial stage of gastric emptying, whereas no effect was seen on the gastric emptying of starch.

The present work was undertaken to study in vivo fibre degradation, rate of passage and caecal fermentation activity (CFA) in the young rabbit (7 weeks old) receiving ad lib. a control (C) or a lowfibre (LF) diet (400 and 220 g neutral-detergent fibre (NDF)/kg respectively). As a consequence of the 50% reduction in the dietary fibre level, the voluntary food intake of the rabbits decreased by 25%, and the daily fibre intake was reduced by 60% (26·7 and 10·8 g NDF/d for groups C and LF, respectively).In spite of a longer mean retention time of the fibre particles, the quantity of fibre digested daily was significantly lower (P<0·01) for the LF than for the C group (4·0 and 7·8 g NDF/d respectively). The circadian distribution of the faecal excretion (as a percentage of the total DM output) did not differ between diets (P = 0·52) and no interaction was found (P = 0·96) between diet and time of excretion. Also, variables describing the CFA showed no interactions between diet (C or LF) and time of sampling (during caecotrophy or during hard faeces excretion). Our results indicated no direct relationship between the quantity of fibre digested and the total short-chain fatty acid concentration in the caecum, but the fermentation pattern indicated lower proportions of acetate for the LF diet. Higher levels of diaminopimelic acid (DAPA) and ATP were found for the LF diet associated with an improved dietary fibre digestibility, suggesting a higher microbial activity. However, this effect was balanced by a lower caecal digesta turnover rate and the microbial biomass output estimated through the faecal DAPA output did not vary significantly

The present study was undertaken to provide detailed information about the effect of dietary fibre (DF)level on the development of the digestive tract, on nutrient digestibility and on energy and protein metabolism of pigs housed in low (13°) or high (23°) thermal environments. Low- and high-fibre diets (59 v. 268 g DF/kg DM) were studied in three balance periods with fistulated pigs in the weight range 45-120 kg. Heat production was measured using open-circuit respiration chambers. Pea fibre and pectin were used to adjust theDF level in the high-fibre diet. Per kg empty body weight the stomach, caecum and colon and the length of colon were significantly greater in pigs consuming the high-fibre diet than in those on the low-fibre diet. Pigs kept at low temperature had significantly heavier caecums than those kept at the high temperature. Digestibilities of protein, DM and energy were lowest for the high-fibre diet. Only minor amounts of NSP and its constituent sugars were degraded anterior to the ileum, whereas in the hind-gut the fermentation of the total NSP fraction was high, being 0·77 for the high-fibre diet and 0·59 for the low-fibre diet. Feeding the high-fibre diet increased the flow of digesta through the terminal ileum 5-6-fold and an extra 460 g organic matter was fermented daily in the hind-gut compared with pigs fed on the low-fibre diet. The amount of retained energy as a proportion of metabolizable energy decreased in relation to the amount of energy fermented in the hind-gut. Based on the present data it was estimated that the relative value of energy derived from hind-gut fermentation was 0·73 in comparison with energy enzymically digested in the small intestine. There was negligible effect of the temperature –fibre interaction on energy metabolism. However, it could be calculated that the decrease in temperature from 23° to 13° was associated with an increase in heat production by 2.9 MJ/pig per d.

The present study was undertaken to provide detailed information about the effect of fibre source (pea fibre, wheat bran or oat bran) at inclusion levels of 0, 187 and 375 g/kg diet on the development of the digestive tract, nutrient digestibility and energy and protein metabolism in broiler chickens. Heat production was measured using open-air-circuit respiration chambers. Diets with increasing levels of pea fibre decreased the DM in droppings and increased excreta output (2·5-fold) relative to DM intake. Adaptation to increased dietary fibre levels included increases in the size of the digestive system, with pea fibre exerting a stronger impact than wheat bran or oat bran. The length of the intestine, and particularly the length and weight of the caecum, increased with the fibre level. The digestibility of all nutrients also decreased with increasing fibre level. The decrease in the digestibility in relation to NSP for the three fibre sources was bigger for oat bran (0·0020 per g dietary NSP) than for pea fibre and wheat bran (0·0014 and 0·0016 per g dietary NSP) indicating that the cell walls in oat bran (aleurone and subaleurone) had a significant negative effect on the digestibility of cellular nutrients, i.e. protein and fat. The degradation of the NSP constituents was far lower in chickens than found in other animal species such as pigs and rats, thus supporting the view that chickens do not ferment fibre polymers to a great extent. Excretion of organic acids (mainly lactic acid and acetic acid) accounted for up to 2% of metabolizable energy (ME) intake with the highest excretion for the high-fibre diets. H2 excretion was related to the amount of NSP degraded and indicated higher microbial fermentation with increasing fibre levels. The chickens' feed intake responded to a great extent to dietary ME concentration but expressed in terms of metabolic body size (W0·75) ME intake was depressed at the high fibre levels. Dietary NSP was able to explain between 86% (oat bran) and 96% (pea fibre) of the variation in ME concentration. The amount of energy available from fermentation of NSP appears to reach a maximum of 42 KJ/d independent of fibre source and level. Expressed in relation to ME intake the NSP fermentation contributed 3-4%. With increasing fibre intake the partitioning of retained energy between body protein and body fat changed in favour of protein.

The urinary excretion of purine derivatives (PD) was measured in six buffaloes (Bubalis bubalis) during fasting and in fourteen buffaloes given four restricted levels of roughage (2·5-4·8 kg DM/d). Only allantoin and uric acid, not xanthine and hypoxanthine, were present in the urine, the pattern of excretion being similar to that in cattle. The fasting PD excretion amounted to 0·20 (SD 0·06) mmol/kg metabolic weight (W0·75) per d, and the rate of PD excretion as a linear function of feed intake was 5·2 mmol/kg digestible organic matter intake. Both values were considerably lower than the values for cattle reported in the literature. Creatinine excretion values were 0·33 (SD 0·06) and 0·44 (SD 0·09) mmol/kg W0.75 per d determined in fasting and feeding periods respectively. Fasting N excretion was 257 (SD 49) mg N/kg W0.75 per d. Both creatinine and fasting N excretions were also lower than in cattle. The activities of xanthine oxidase (EC 1.2.3.2) in plasma, liver and intestinal mucosa were determined in buffaloes, cattle and sheep. Xanthine oxidase activities in buffaloes were 24·5 (SD 2·7) unit/l plasma and 0·44 (SD 0·02) and 0·31 (SD 0·10) unit/g fresh tissue in liver and intestinal mucosa respectively. These activities were higher than those in cattle and sheep. Xanthine oxidase was practically absent from plasma and intestine of sheep. It is suggested that the differences in PD excretion between buffaloes and cattle were probably due to the smaller proportion of plasma PD that was disposed of in the urine of buffaloes.

The correlations between the mean of 4 d weighed intakes of lutein, lycopene and βcarotene and mean plasma concentations during each of the four Seasons were lutein r 0·64, lycopene r 0·47 and βcarotene r 0·45. Intake was not significantly correlated with plasma concentrations during every seasonal time-point. There was a significantly higher intake of lutein during the spring compared with summer and autumn, lycopene intake was significantly higher during the summer and autumn and there were no significant seasonal differences in β-carotene intake. There were, however, significant seasonal differences in plasma carotenoid concentrations, the highest levels occumng between May and October. There were large inter- and intra-individual variations in intake and plasma concentrations of carotenoids. BMI was inversely correlated with plasma βcarotene (r-0·41). The findings suggest that plasma carotenoid concentrations are indicative of dietary intake, but the large intra-individual variation in plasma concentrations indicates that any assessment of longer-term status from data at any one time-point should be treated with caution.

The contribution of breakfast to mean daily energy and nutrient intakes was investigated in a sample of 7-8-year-old children recruited by letter from five Scottish schools. After eighteen families dropped out of the study and three dietary records were discarded, thefinal sample numbered 136 (51%). Dietary data were collected using the 7 d weighed inventory, while a questionnaire was used to classify children into manual or non-manual social class groups. Mean daily energy intakes were close to estimated average requirements (Department of Health, 1991), while intakes of most micronutrients were in excess of reference nutrient intakes (RNI; Department of Health, 1991). The most popular breakfast consumed by the children was oneincluding a ready-to-eat breakfast cereal (RTEBC). Differences in macronutrient content were seen between breakfasts of boys and girls, while manual-social-class children ate breakfasts which were lower in energy, NSP and certain micronutrients than those of non-manual-class children. Breakfast contributed 14% of energy and 9-36% of micronutrient intakes to the overall diets.Breakfasts including RTEBC contributed significantly more energy and nutrients than other types of breakfast. Children who ate RTEBC nearly every day had overall diets which had a highernutrient density and were lower in fat than those of children who ate RTEBC less frequently ornot at all. Intakes of most micronutrients were above tbe RNI in both these groups, with the exception of folate, Fe and vitamin A, which were below the RNI for those consuming RTEBC infrequently. However, the type of breakfast eaten did not appear to influence energy and nutrient intakes at other meals during the day.Nevertheless, it was concluded that breakfast, particularly one containing RTEBC, had a strong influence on the daily energy and nutrient intakes of 7-8-year-old children, particularly by reducing the proportion of energy from fat.

Dietary proteins are degraded by both endogenous enzymes and the caecal microflora. In conventional rats the enzyme content of the pancreas depends on the amount of dietary protein. The influence of the caecal microflora on this process is unknown. We report here the effect of the caecal microflora on pancreatic enzymes (proteases, amylase (EC 3.2.1.l), lipase (EC 3.1.1.3)) and on colonic metabolites (NH3, urea, short-chain fatty acids). Germ-free and conventional male Fischer rats were fed for 3 weeks with a diet containing 220 or 450 g protein/kg provided as a mixture of fish concentrate and soyabean isolate. The excretion of NH3, and the pH were specifically increased by the high-protein diet in the germ-free rats. The higher production of isobutyrate, valerate and isovalerate in conventional rats fed on the high-protein diet reflected a high bacterial proteolytic activity since these short-chain fatty acids are specific indicators of this activity. The microflora hydrolysed urea to NH3 and maintained the pH at neutrality whatever the amount of protein in the diet since there were changes in germ-free rats but not in conventional ones. In germ-free rats, amylase, trypsin (EC 3.4.21.4), elastase (EC 3.4.21.36) and carboxypeptidase A (EC 3.4.17.1) specific activities were significantly lower than in conventional rats. The adaptation of the pancreas to the 450 g protein/kg diet was not impaired by the bacterial status except for the specific activity of chymotrypsin (EC 3.4.21.1) which was more increased by this diet in germ-free than in conventional rats. Moreover, the specific activity of lipase increased only in conventional rats fed on the 450g protein/kg diet. In conclusion, we observed a relationship between the enzyme content of the pancreas and the presence or absence of the caecal microflora suggesting that bacterial fermentation influences pancreatic function.

A direct comparison of systemic (spleen) and mucosal (intestine) antibody-producing systems was made in weanling male C57BL/6J mice subjected to wasting protein-energy malnutrition (PEM) by means of a low-protein protocol known to duplicate immunological and physiological features of human malnutrition. ELISA revealed low concentrations of biliary and gut lumen immunoglobulin (Ig) A in malnourished mice concomitantly with a high concentration of blood IgA. The low-protein model, therefore, exhibited fidelity to human protein-energy malnutrition in its influence on the concentrations of the mucosal Ig, IgA, in critical biological fluids. The number of IgA-, IgM- and IgG-containing cells was estimated morphometrically on a per organ basis. The low-protein protocol supported expansion in numbers of mucosal IgA-containing cells (18 x relative to a zero-time control group) and of splenic IgG- containing cells (135 x ), albeit an attenuated expansion in comparison with that of well-nourished control animals (132x and 571x respectively relative to zero-time controls). Up to terminal differentiation of Ig-containing cells, systemic and mucosal antibody-producing systems exhibited similarly remarkable resistance to wasting malnutrition. Epithelial transport of IgA may be an aspect of the mucosal antibody response which is particularly sensitive to PEM.

The hypothesls was tested that fermentable dietary fibre (DF) sources elevate faecal N excretion at the expense of urinary N without affecting N retention. DF that substantially increase fermentation (pectin, Sugarbeet and soya bran) or are poorly fermented (crystalline cellulose and maize bran) were fed as supplements to a basal DF-free diet a t three dose levels: 0,50 and 100 g supplement/kg basal diet. The diets were fed to juvenile male Wistar rats for 2 weeks before a 7 d period when faeces and urine were collected. Faecal excretion of N was significantly increased, dose-dependently, by all DF supplements and was positively correlated to faecal bulking. Urinary excretion of N was lower at the high doses of the DF supplements but reached significance only with the highly fermentable (0·68) sugarbeet- supplementeddiets. Regression analysis showed that the major part (0·75) of the increase in faecal N excretion due to DF supplementation was balanced by a reduction in urinary excretion; N retention was therefore, at the dose levels used, only affected to a small extent. Only in the maize-bran-supplemented diets were the reductions in N retention significant. The shift in N excretion from urine to faeces can be explained largely by the degree of microbial fermentation in the large intestine caused by the addition of DF supplements and emphasizes the modifying role that certain DF supplements may have on the enterohepatic cycle of N. Possible implications of these findings for patients with liver or renal failure or for conditions when the intake of dietary protein is marginal are discussed.

The purpose of the present study was to assess the role of the liver in the plasma-cholesterol-lowering effect of soyabean lecithin. Normolipidaemic rats were fed on lecithin-enriched or control diets with the same amount of protein. The lecithin diets contained 200 g/kg high-fat commercial semi-purified soyabean lecithin (230 g/kg total lipids as soyabean phosphatidylcholine) or 200 g/kg high-fat purified soyabean lecithin (930 g/kg total lipids as soyabean phosphatidylcholine). The control diets were a low-fat diet (40 g fat/kg) and a high-fat triacylglycerol-rich diet (200 g fat/kg). The high-fat diets were isoenergetic. The cholesterol-lowering effect of the lecithin-enriched diets was associated with significantly lower levels of plasma total- and HDL-cholesterol and significantly higher levels of bile phosphatidylcholine (PC), bile salts and cholesterol. These findings suggest that the liver plays a major role in the reduction of plasma cholesterol, the increased biliary lipid being provided by both HDL and the hepatic microsomal pools of PC and cholesterol.

The effects of dietary fat and dietary fibres on blood pressure, serum lipids and platelet aggregation in spontaneously hypertensive and Wistar-Kyoto rats have been investigated. The systolic and diastolic blood pressure values were increased with increasing amounts of dietary fat and normalized by dietary fibre supplementation. The greatest reduction in blood pressure was obtained by a combination of reduced dietary fat and supplementary dietary fibre. Addition of dietary fibre when the amount of dietary fat was high or reduction of dietary fat when the amount of dietary fibre was low gave a smaller effect. In both rat strains the decreases in systolic and diastolic blood pressure values after reducing dietary fat and/or increasing dietary fibre were about 10-15 mmHg. Serum total cholesterol and serum HDL-cholesterol concentrations were reduced by reduction of dietary fat or a combination of dietary fat reduction and dietary fibre addition. A combination of dietary fat reduction and dietary fibre addition was the most effective dietary change for reducing serum triacylglycerol concentration and platelet aggregation. The present study demonstrates that in this experimental model it is possible to reduce risk indicators of coronary heart disease significantly by changing dietary habits.

Abstract Increased Ca intake by adolescents is desirable. In order to achieve this, information on the current dietary sources of Ca by this age group is essential to enable change to build on existing habits. This paper addresses two issues: first, the dietary sources of Ca for adolescents are reported and, second, the importance of fortification of flour with Ca to present-day Ca intakes was determined. In 1990 the diets of 379 children aged 12 years were assessed using the 3 d dietary diary and interview method. Computerized food tables were used to calculate the contributions of different food groups to total Ca intake. The Ca content of eachfood was subdivided into naturally occurring Ca and Ca from fortification, and data were analysed to give the daily intake of each. The four most important sources of Ca were milk (25%), beverages (12%), puddings (10%) and bread (9%). Fortification of flour accounted for 13% of total Ca intake. When the contribution of fortification was removed, the proportion of subjects with intakes of Ca below the lower reference nutrient intake (Department of Health, 1991) increased more than fourfold, to 10% of girls and 12% of boys. Milk is contributing less to Ca intake than in the past and increased consumption should be encouraged. Ca fortification of flour remains an important source of Ca. Therefore, unless dietary habits are modified to ensure adequate Ca from other sources, increased consumption of unfortified products from outside the UK will lead to a further reduction in Ca intake.