In a recent article in the British Journal of Nutrition, Sklan & Dariel (1993) presented a method for diet planning employing a mixed-integer programming algorithm for meeting nutritional requirements at minimum costs for institutions or individuals. They recognized that most food items are generally consumed in whole units and as such they are represented as integer variables. However, as in most previous studies, they derived the minimum cost diets by optimizing over purchased food items. The present paper presents a computer-assisted, diet-planning modelling system for individuals by optimizing over recipes instead of food items. This is accomplished by restricting the integer programming solutions to those bundles of food that represent reasonably popular meal recipes. The modelling system is composed of three main components: recipe data entry, database management, and the model. The recipe data entry component creates and stores recipes. It aiso provides nutritional analysis of the recipes. The database management component creates and maintains several databases necessary to build the modelling data file. The modelling component solves the user-specified model. Currently, the model component can solve for the optimal diet by minimizing cost or minimizing cooking and preparation time. The optimal diet is prepared to satisfy the recommended nutritional guidelines for a predefined group of individuals for 1 week. The system currently has 895 popular recipes found in Hawaii. Diet plans generated using this modelling system with differing objectives are discussed and compared.

A slaughter experiment was carried out to study the effect of dietary protein quality on maintenance energy requirements and energy costs for protein accretion and fat deposition in fast-growing broiler-type male chickens. Three isonitrogenous (200 g crude protein/kg DM) and isoenergetic (14 kJ metabolizable energy (ME)/g DM) semipurified diets based on soyabean meal unsupplemented (diet S) or supplemented with 20 g L-lysine/kg (diet SL) or 2 g DL-methionine/kg (diet SM), in order to promote a decrease or an increase in growth rate respectively, were selected and given at four feeding levels (ad lib. or restricted to 40, 28 and 18 g DM/d, on average) to 10-d-old fast-growing male broiler-type chicks for 2 weeks. Both the efficiency with which ME was used to support growth (kg) and the maintenance requirements (MEm) significantly decreased inversely to the biological value of the dietary protein (kg = 0·660, 0·600 and 0·572; MEm = 597, 522 and 464 k.J/kg W0·75 per d, for diets SI, S and SM respectively). The partial efficiencies of use of ME for protein accretion (kp) or fat deposition (kf) were also inversely related, the former increasing with the quality of the protein offered. An alternative procedure was used to try to overcome the statistical problems inherent in the partition of ME between fat and protein.

The effect of dietary protein concentration on stress responses against injection of Escherichia coli lipopolysaccharide (LPS) was studied in male broiler chickens. Chickens (7 d of age) were fed on a 100 (low-protein; LP) or 300 g protein/kg (high-protein; HP) diet for 2 weeks. LPS was injected intraperitoneally every 2 d during the final 6 d, or once 16 h before the end of the experiment, at a concentration of 900 μg/chick. The LPS injection did not affect body-weight gain, feed intake, gain:intake ratio, or plasma Fe concentration. The single injection of LPS reduced plasma Zn concentration, but the repeated injections did not. Feeding the HP diet increased the response of plasma Zn concentration to the single injection of LPS. Plasma albumin concentration was reduced by LPS injection. Feeding the HP diet resulted in a higher plasma α 1-acid glycoprotein (AGP) concentration than feeding the LP diet, in chicks untreated with LPS. An increase in plasma AGP concentration observed after LPS injection in chicks fed on the LP diet was greater than that seen in chicks fed on the HP diet. No significant changes in plasma AGP concentration in response to repeated injections of LPS were observed in chicks fed on the HP diet. Plasma interleukin-1 (IL-l)-like activity was greater in chicks fed on the LP diet than in those fed on the HP diet, when LPS was injected. The response of plasma IL-1-like activity to the single injection of LPS in chicks fed on the LP diet was the greatest among the treatment groups. These results suggest that acute-phase responses to LPS injection are much greater in chicks fed on a LP diet than in those fed on a HP diet, and multiple injection of LPS weakens the responses.

An experiment was designed to test the prediction that two genetically-very-different kinds of pigs would retain the same amounts of protein in their bodies when given the same allowances of the same feed for the same period of time, when these allowances were limiting for both. An allowance of 33·957 kg of a feed with 12·76 MJ metabolizable energy (ME) and 189 g crude protein (N × 6·25)/kg feed was given to Large White × Landrace (LW ×) and Chinese Meishan (CM) female pigs over three different periods of time: (1) ad lib. (AL) with the time taken by individual pigs to consume the allowance being a variable, (2) over a period of 7 weeks (H) and (3) over a period of 9 weeks (L). In addition, in a fourth treatment, pigs of both breeds received the same allowance but supplemented with starch also over a period of 7 weeks (HS). The performance of the pigs on treatment AL was affected by pig breed, with CM pigs gaining protein at a slower, and lipid at a faster, rate than LW × pigs. On treatments L, H and HS the average amounts of protein retained were 2·693 and 2·655 kg for the LW × (n 15) and CM (n 15) pigs respectively (SED 0·106 kg). There was a statistical indication that the LW × pigs may have been more efficient on L, and less efficient on HS, than the CM pigs but we have been unable to propose any biological reason for such an effect, if it was in fact a real one. Thus, the efficiency with which ideal protein was utilized was close to being constant, and apparently at its maximum, for the two breeds. However, although CM pigs had the same protein gain, and the same live weights, on the same feed allowances as the LW × pigs, they gained significantly more lipid. This was attributed in part to their digesting their feed better and in part to their having a lower energy requirement for maintenance through a lower level of physical activity. Given that these two very different kinds of pigs use limiting protein with the same efficiency, it is suggested that it is safe to make the assumption in models of pig growth that the material efficiency of using limiting protein is constant across genotypes of pig.

Propionate is a short-chain fatty acid formed in the colon and supposedly involved in the cholesterol-lowering effect of soluble fibre. To explore the underlying mechanism(s) of this fibre action, we have used human hepatocytes in primary culture to study the effects of propionate on hepatic lipid synthesis. Initial experiments with mevalonate and mevinolin, a competitive inhibitor of hydroxymethylglutaryl (HMG)-CoA reductase (EC 1·1·1·88) were performed to evaluate basic regulatory mechanisms in these cells; results were compared with those obtained with rat hepatocytes. Incubation for 24 h with mevalonate caused a similar, concentration-dependent inhibition of [14C]acetate incorporation. into cholesterol in human and rat hepatocytes. Likewise, mevinolin (100 μmol/l) inhibited the formation of cholesterol from radiolabelled acetate by about 80% in cells from both species. Propionate inhibited cholesterol as well as triacylglycerol synthesis from [14C]acetate with a similar concentration-dependency in rat hepatocytes. Fifty percent inhibition was obtained at a propionate concentration of only 0·1 mmol/l· This propionate-induced inhibition was not affected by a 100-fold excess of unlabelled acetate. Human hepatocytes were much less susceptible in this respect: propionate concentrations of 10–20 mmol/l were required to obtain similar inhibitory effects in these cells, i.e. values greatly exceeding reported portal propionate concentrations in humans. The results suggest the existence of differences in the regulation of hepatic cholesterol (and triacylglycerol) synthesis between human and rat liver cells. These results do not support the hypothesis that the fibre-induced decrease in plasma cholesterol concentration in man is mediated by a direct effect of propionate on hepatic cholesterol synthesis.

In the present study the actual role of propionic acid in the control of fatty acid and cholesterol synthesis was investigated in isolated liver cells from fed rats maintained in the presence of near-physiological concentrations of glucose, glutamine and acetate. Using 3H2O for lipid labelling, propionate appears as an effective inhibitor of fatty acid synthesis and to a lesser extent of cholesterol synthesis, even at the lowest concentration used (0·6 mmol/l). Butyrate is a potent activator of both synthetic pathways, and the activating effect was not counteracted by propionate. Using 1-[14C]acetate, it was observed that propionate at a moderate concentration, or 1 mmol oleate/l, are both very effective inhibitors of 14C incorporation into fatty acid and cholesterol. This incorporation was drastically inhibited when propionate and oleate were present together in the incubation medium. The net utilization of acetate by rat hepatocytes was impaired by propionate, in contrast to oleate. 1-[14C]butyrate was utilized at a high rate for fatty acid synthesis, but to a lesser extent for cholesterol synthesis; both processes were unaffected by propionate. Intracellular citrate concentration was not markedly depressed by propionate, whereas it was strongly elevated by butyrate. In conclusion, propionate may represent an effective inhibitor of lipid synthesis when acetate is a major source of acetyl-CoA, a situation which is encountered with diets rich in readily-fermentable fibres. The present findings also suggest that propionate may be effective at concentrations close to values measured in vivo in the portal vein.

The association of radiolabelled taurocholic acid with the solid fraction of a faecal fermentation mixture was measured. A human faecal inoculum was incubated with [24-14C]taurocholic acid and several non-starch polysaccharide sources (pectin, wheat bran, ispaghula (Plantago ovata) husk and seed), glucose or a substrate-free control. Portions of fermentation mixture were taken at 0, 3, 6, 21 and 24 h and centrifuged to acquire a supernatant fraction and a pellet containing the fermentation residue. 14C was measured in supernatant fractions and pellets at all time points. Volatile fatty acids (VFA) were measured at 0 and 24 h to confirm bacterial growth. Radioactivity in the pellet increased over time for all substrates. Glucose resulted in the greatest incorporation of taurocholic acid into the pellet, followed by pectin. At 24 h the proportion of the total radioactivity found in the pellet was 92% for glucose, 79% for pectin, 60% for wheat bran, 59% for ispaghula seed, 53% for ispaghula husk and 26% for the control (mean of duplicates). Glucose and pectin produced the greatest quantity of VFA at 24 h. VFA production was highly correlated with radioactivity in the pellet (r 0·976, P <0·005). These results suggest that the bile acid binding capacity of a faecal culture mixture may be strongly influenced by the fermentability of the available substrate and hence related to bacterial metabolic activity.

The effects of oat saponins (a mixture of avenacosides A and B) and dietary fibre (cellulose and guar gum) on the disaccharidase activities in the proximal small intestine of the rat were investigated. The influence of avenacosides A and B on the activity of disaccharidases and α-amylase (EC 3·2·1·1) was also studied in vitro. In vivo, oat diets with three avenacoside contents (negligible, normal and twice normal) were used. No significant differences in sucrase (EC 3·2·1·48), maltase (EC 3·2·1·20), trehalase (EC 3·2·1·28) and lactase (EC 3·2·1·21) activities were found between the oat groups after 19 d feeding. The rats that were given cellulose tended to have higher disaccharidase activities compared with the other groups. The avenacosides inhibited the lactase activity significantly in vitro while no or small effects on the other disaccharidases were found. In contrast, the in vitro hydrolysis of starch by α-amylase was increased in the presence of saponins, probably due to their detergent effect. Thus, the in vitro studies showed that the avenacosides could influence the enzyme activities. In vivo, these effects are probably minor due to the low avenacoside concentrations found in oats.

It is known that the physico-chemical characteristics of fibre modify their fermentation characteristics in the colon. Previously we showed the varying effects of inulin and different types of fibre on the hepatic and intestinal xenobiotic-metabolizing enzymes (XME) in initially germ-free rats inoculated with a human, methanogenic, whole-faecal flora (Roland et al. 1994). The aim of the present work was to assess whether or not these effects could be related to differences in production of fermentation metabolites (gases excreted in vivo and caecal metabolites) due to the different compositions of fibre. The different types of fibres were analysed with regard to their solubility and their composition of neutral monomers and uronic acids. Inulin was totally soluble, carrot (Daucus carota), cocoa (Theobroma cacao) and wheat bran were partially soluble; pea (Pisum sativum) and oat were nearly totally insoluble. Uronic acids were found mostly in carrot and cocoa fibre. Glucose was present as the main neutral monomer in each fibre type. Xylose was found also in wheat bran, pea and oat fibres, and arabinose was found in wheat bran. Inulin consumption led to high levels of H2 production but no CH4 production, to a 4-fold greater caecal concentration of butyrate than with the other fibres and to a decrease in caecal pH. Conversely, rats fed on carrot or cocoa fibre produced a large amount of CH4 but no H2 and generated a different profile of short-chain fatty acids (SCFA). The lowest amounts of gases and SCFA were found in rats fed on wheat bran, pea and oat fibre. We observed a relationship between the caecal concentration of SCFA and the activity of hepatic glutathione-S-transferase (EC 2·5·1·18) but no direct link was shown between the other XME and the fermentation profile.

Milk and yoghurt proteins were 15N-labelled in order to measure the flow rate of exogenous N during digestion in the human intestine. After fasting overnight, sixteen healthy volunteers, each with a naso-jejunal tube, ingested either [15N]milk (n 7) or [15N]yoghurt (n 9). Jejunal samples were collected every 20 min for 4 h. A significant stimulation of endogenous N secretion was observed during the 20–60 min period after yoghurt ingestion and the 20–40 min period after milk ingestion. The endogenous N flows over a 4 h period did not differ between the groups (44·3 (SEM 6·5) mmol for milk and 63·5 (SEM 5·9) mmol for yoghurt). The flow rates of exogenous N indicated a delayed gastric emptying of the yoghurt N compared with N from milk. The jejunal non-protein N (NPN) flow rate increased significantly after milk and yoghurt ingestion due to an increase in the exogenous NPN flow rate. The NPN fraction of exogenous N ranged between 40 and 80%. The net gastro-jejunal absorption of exogenous N did not differ significantly between milk (56·7 (SEM 8·5)%) and yoghurt (50·9 (SEM 7)%). The high level of exogenous N hydrolysis is in accordance with the good digestibility of milk products. Fermentation modifies only the gastric emptying rate of N and does not affect the level of diet hydrolysis, the endogenous N stimulation or the digestibility rate.

A defective thermic response to food may be an energy-sparing adaptation in both obesity and pregnancy. To evaluate the combined effect of obesity and pregnancy on postprandial thermogenesis, the thermic effect of food was assessed for a 240 min period following a high-carbohydrate meal and a typical mixed meal in nine normal-weight non-pregnant, eight overweight non-pregnant, eight normal-weight pregnant and six overweight pregnant women using indirect calorimetry. A test meal that provided 60% of each subject's measured daily requirement for basal metabolism was used. Pregnant women were studied during weeks 30–35 of gestation. Neither obesity nor pregnancy altered the thermic effect of food, although the response to the mixed meal was greater (P <0·01) than that to the high-carbohydrate meal in all cases. The mean responses for the high-carbohydrate and mixed meals were 26·9 (SD 6·0) and 30·1 (SD 6·2)% baseline energy expenditure respectively, and 7·4 (SD 1·6) and 8·3 (SD 1·6)% of the meal energy load respectively. Obesity and pregnancy were associated with hyperinsulinaemia (P <0·005) following both test meals, suggesting that postprandial thermogenesis was not altered by insulin resistance in this group. The incremental glucose response was elevated (P <0·001) in the pregnant women following both test meals; overweight women tended to have a greater incremental glucose response following the high-carbohydrate meal, but it was not significant (P = 0·065). These results do not provide evidence of an impaired thermic response to food in either overweight or third trimester pregnant women.