Deuterium dilution for the measurement of total body water (TBW) has been conducted using varying protocols for equilibration. We measured TBW from deuterium dilution in urine samples in twenty-eight subjects using three protocols: (1) early morning dosage without breakfast, measuring deuterium in a second voiding at 4h and 6h; (2) early morning dosage with breakfast with the same measurement times; (3) dosage as last consumption before overnight sleep, measuring deuterium in a second voiding at 10 h. Results were compared with TBW estimates from underwater weighing (UWW). Because UWW is an indirect measure of TBW, it is used as an independent reference method in order to compare only relative discrepancies between the two methods. TBW values in the fasted state were not significantly different from those obtained in the fed state. The urinary deuterium enrichment was higher at 4 h than at 6 h (resulting TBW differences: 0·6 (SD 0·4)I). At 4h and 6h, differences in TBW measurements from deuterium and densitometry were positively related to the amount of TBW, indicating incomplete equilibration in larger water compartments. At 10h no such relationship existed, indicating complete mixing of deuterium. It is concluded that 10h equilibration is preferable to the shorter 4h and 6h, for the determination of TBW.

Estimates of food consumption and macronutrient intake were obtained from a randomly selected population sample (2%) of 1015 adolescents aged 12 and 15 years in Northern Ireland during the 1990/1991 school year. Dietary intake was assessed by diet history with photographic album to estimate portion size. Reported median energy intakes were 11.0 and 13.1 MJ/d for boys aged 12 and 15 years respectively and 9.2 and 9.1 MJ/d for girls of these ages. Protein, carbohydrate and total sugars intakes as a percentage of total energy varied little between the age and sex groups and were approximately 11, 49 and 20 % respectively of daily total energy intakes. Median dietary fibre intakes were approximately 20 and 24 g/d for boys aged 12 and 15 years respectively and 18 and 19 g/d for girls of these ages. Major food sources of energy (as a percentage of total energy intakes) were bread and cereals (15–18 %), cakes and biscuits (12–14%), chips and crisps (13–14%), dairy products (9-ll%), meat and meat products (9–11%) and confectionery (9%). Fruit and vegetable intakes were low at about 2.5% and 1.5% respectively of total energy intakes. Median fat intakes were high at 39% of total daily energy intakes. Major food sources of fat as a percentage of total fat intakes were from the food groupings: chips and crisps (16–19%), meat and meat products (14–17%), fats and oils (14–16%), cakes and biscuits (13–16%) and dairy products (12–15%). Median intakes of saturated fatty acids were also high at approximately 15% of daily total energy intake while intakes of monounsaturated fatty acids averaged 12% of daily total energy intake. Median polyunsaturated fatty acid (PUFA) intakes were low, comprising 5.2 and 5.5 % of daily total energy intake for boys aged 12 and 15 years respectively and were lower than the PUFA intakes (59 and 6.3% of daily total energy intake) for girls of these ages. About 1.3 % for boys and 1.4 % for girls of daily total energy intake was in the form of n-3 PUFA. Ca and Mg intakes were adequate for both sexes. Based on these results, some concern about the dietary habits and related health consequences in Northern Ireland adolescents appears justified.

A 60 % reduction in maternal feed intake is known to cause a reduction of approximately 20 % in biceps brachii fibre number in the guinea-pig fetus. This investigation was designed to isolate the dietary component responsible by reducing all dietary components to 60 % of the ad lib. level and supplementing the protein, carbohydrate or fat component to the level of the ad lib. intake. Fetal muscles were examined at 50 d gestation to determine numbers of primary and secondary fibres, and at term to determine total fibre number. Fetal and neonatal weights were reduced in all restricted groups (P < 0.05) when compared with ad lib. controls. At term this reduction was significantly less (P < 0.05) in the protein-supplemented group (20%) than in the 60 %-restricted and fat-supplemented groups (43%) and the carbohydrate-supplemented group (34%). Biceps brachii fibre numbers were reduced in the 60%-restricted and fat-supplemented groups by 14–16%, but fibre numbers were similar in control, protein-supplemented and carbohydrate-supplemented groups. Any reduction in fibre number was in the secondary fibre component of total fibre number. Therefore, biceps brachii fibre numbers were reduced only when maternal diets were deficient in both protein and carbohydrate.

Fifty-one male and female volunteers aged 18–90 years from a wide variety of social and occupational backgrounds completed 7284 assessments of portion size in relation to food photographs. Subjects were shown six portion sizes (two small, two medium and two large) for each of six foods, and asked to compare the amount on the plate in front of them to (a) a series of eight photographs showing weights of portions from the 5th to the 95th centile of portion size (British Adult Dietary Survey), or (b) a single photograph of the average (median) portion size. Photographs were prepared either in colour or in black and white, and in two different sizes. The order of presentation of foods; use of black and white or colour; the size of photographs; and presentation of eight or average photographs were each randomized independently. On average, the mean differences between the portion size presented and the estimate of portion size using the photographs varied from -8 to + 6g (-4 to + 5%) for the series of eight photographs, and from -34 to −1g (-23 to + 9%) for the single average photograph. Large portion sizes tended to be underestimated more than medium or small portion sizes, especially when using the average photograph (from -79 to -14g, -37 to -13%). Being female, 65 years and over, or retired, or seeing photographs in colour, were all associated with small but statistically significant overestimations of portion size. Having a body mass index ≥ 30 kg/m2 was associated with an 8% underestimate of portion size. We conclude that use of a series of eight photographs is associated with relatively small errors in portion size perception, whereas use of an average photograph is consistently associated with substantial underestimation across a variety of foods.

To test the hypothesis that subclinical gastrointestinal parasitism, associated with an impairment in N digestion and metabolism and a reduction in the voluntary feed intake (VFI), could affect the diet selection of sheep given a choice between two feeds that differed in their crude protein (CP) content, twenty-four Texel ×Scottish Blackface ewe lambs growing from 28 to 48 kg live weight (LWT) were given a daily dose of 2500 larvae of the intestinal nematode Trichostrongylus colubriformis; twenty-four similar lambs were used as uninfected controls. Six infected and six control lambs were given a free choice between two pelleted feeds (10·4 MJ metabolizable energy/kg), wilh different CP contents (90 (L) and 214 (H) g CP/kg fresh feed respectively). In addition, eighteen parasitized and eighteen control sheep were given access ad lib. to either feed L, or feed H, or their mixture M (164 g CP/kg; twelve per feed), in order to quantify the effects of the feeds when offered alone, and to test for any interactions between feed CP content and parasitism on the performance of the lambs. Intestinal parasitism reduced significantly (P < 0·001) both the rates of LWT gain (by 30%) and VFI (by 10%). The adult and developing parasitic forms took 4 weeks to establish and develop to a significant adult worm population (as judged by the faecal egg counts and blood variables) and until then there was no effect of parasitism on the performance of the lambs. The diet selection of the lambs given a choice between two feeds was similar between the two groups in the first 4 weeks of the experiment, but differed significantly (P < 0·05) in the second part of the experiment (4th week to the end). Thus, while parasitized lambs had a reduced rate of feed intake, by changing their diet selection they achieved a daily rate of CP intake similar to the control ones. However, since the parasitized lambs had a reduced rate of LWT gain, they also consumed a higher total amount of CP to reach the same LWT. It is concluded that sheep infected daily with a small number of larvae of T. colubriformis and given a choice between two feeds that differ in their protein contents are able to modify their diet selection in order to meet the increased protein requirements resulting from such an infection.

Seventy piglets with no access to creep feed were weaned at 28 d of age and fed on one of four diets based on either skimmed-milk powder (SMP), soya-bean-protein concentrate (SPC), soya-bean meal (SBM) or fish meal (FM). At 0, 3, 6 and 10 d after weaning, piglets were killed and the pancreas and digesta from stomach and small intestine were collected, freeze-dried and analysed for dry matter (DM), N, and trypsin (EC3.4.21.4) and chymotrypsin (EC3.4.21.1) activities. Small-intestinal tissue samples were taken to examine gut wall morphology. Results indicated that dietary protein source affected post-weaning feed intake, pancreatic weight, gastric pH and gastric protein breakdown, and pancreatic and jejunal trypsin and chymotrypsin activities. Post-weaning feed intake appeared to be an important factor in digestive development of newly-weaned piglets.

Measurement of energy expenditure with doubly-labelled water and of body composition and breast milk output with 2H or 18O requires accurate and precise techniques for measuring isotopic enrichments. The possibility of an inaccuracy in measurements of 2H and 18O isotopic enrichment arising from the matrix in biological fluids was investigated (1) by simulating a dilution experiment in both water and urine samples and (2) by reconstituting urine samples, ranging from 10 to 60 g/kg in solid concentration, from freeze-dried urinary solids mixed with either natural abundance or doubly-labelled water. Current techniques involved in measuring 2H and 18O isotopic enrichments were used (reduction of the samples to H2 gas with either Zn or U, and CO2/H2O equilibration or direct measurement of mass 20:18 ratios on water vapour for 18O analysis). All four methods accurately measured serial dilutions in both urine and water. Dilution space calculated from isotopic enrichments, compared with the water content of urine (determined by freeze-drying and accounting for exchangeable isotopes) was overestimated by about 2.4 % by the Zn technique whereas other methods were accurate. The urinary solids content of a water solution was related to that inaccuracy. The use of the Zn technique with biological samples is likely to create biases in 2H distribution space. Examination of recent literature supports this view. Caution should therefore be used when physiological conclusions have to be made from the relative size of 2H and 18O distribution spaces.

Changes in tissue protein synthesis and an associated membrane transport system in rats were investigated during lactation and under conditions of dietary protein restriction. Following mating, female Sprague-Dawley rats (second parity) were caged individually and offered a high-protein diet (H; 215 g crude protein (N × 6.25; CP)/kg dry matter (DM)) ad lib. until day 12 of gestation. Subsequently half continued to receive diet H, whilst the remainder were offered a low-protein diet (L; 65 g CP/kg DM) until parturition. On day 1 of lactation females were then allocated to either diet H or another low-protein diet (L2; 90 g CP/kg DM) which were offered ad lib. until day 13 of lactation, giving four lactation groups HH, LH, HL2 and LL2. On days 1 and 13 of lactation groups of females were used in the estimation of tissue protein synthesis (flooding dose of [3H] phenylalanine) and Na+, K+-ATPase (EC 3.6.1.3) activity (polarographically) in skeletal muscle, mammary gland, liver and duodenal mucosa. By day 1 of lactation diet L had reduced fractional and absolute synthesis rates (FSR and ASR) of muscle protein (P < 0.05) and the O2 consumption associated with Na+,K+-ATPase, although not significantly (P < 0.10). Rates of protein synthesis in the other tissues studied were not affected on day 1 of lactation by the gestation dietary treatment. By day 13 of lactation the feeding of diet L2 had reduced muscle FSR and ASR of group HL2 to rates that were lower than those on day 1 (P < 0.05), comparable to those of group LL2 and lower than those of groups HH and LH (P < 0.05). Diet H had allowed group LH to increase their muscle protein synthesis compared with that on day 1 (P < 0.05). Muscle Na+,K+-ATPase activity on day 13 of lactation was also lower in groups offered diet L2 (P < 0.05). Mammary protein synthesis was increased during lactation with the feeding of diet H (P < 0.05), which was prevented by diet L2 such that rates of groups HL2 and LL2 were lower than those of the two high-protein groups on day 13 (P < 0.01). Mammary respiration and in particular Na+,K+-ATPase activity was increased during lactation by the feeding of diet H (P < 0.05). Rates of protein synthesis and respiration in liver and duodenal mucosa were not significantly affected by the gestational or lactational dietary treatments. Calculated rates of muscle protein degradation suggest that whilst the loss of muscle protein in group HL2 during lactation might have been promoted by the decline in synthesis, the increase in degradation may have been quantitatively more important.

The effect of dietary protein quality and quantity on fractional rates of protein synthesis (ks) and degradation (kd) in the skeletal muscle, liver, jejunum and skin of young growing chickens was studied. Chickens were either fasted overnight or were fed at frequent intervals, using continuous feeders, with equal amounts of a diet containing soya-bean meal as the sole protein source, unsupplemented, or supplemented with either lysine or methionine. Each of the three diets was provided at 2 or 0.9 × maintenance. On the higher intake, birds on the unsupplemented diet gained weight, lysine supplementation decreased and methionine supplementation increased body-weight gain (by −23% and + 22% respectively). Birds led at 0.9 × maintenance lost weight; supplementation with methionine or lysine did not influence this weight loss. None of the dietary regimens had significant effects on protein synthesis rates in any of the tissues, thus the mechanism whereby muscle mass increased in response to methionine supplementation appeared to be a decrease in the calculated rate of protein degradation. Similarly, on the 0.9 × maintenance diet the failure of the animals to grow appeared to be due to an increase in the rate of protein degradation rather than an effect on synthesis. Conversely, muscle ks was decreased in fasted chickens previously fed on the unsupplemented diet at 2 × maintenance, and in birds which had received the 0.9 × maintenance diet fasting resulted in a similar reduction in protein synthesis in muscle; ks in the liver and jejunum was also significantly decreased. The effect of fasting, unlike the effect of supplementation or restriction of the diet, appeared to be due to changes in the rate of protein synthesis.

Energy expenditure was measured over 10 d using the doubly-labelled water (DLW) and activity diary methods in summer and winter in subjects with ‘light’ occupations but leisure activities which ranged from ‘non-active’ to ‘very active’. The basal metabolic rate (BMR) and the energy cost of activities were determined by indirect calorimetry. The Department of Health (1991) predicted BMR for the group (6·89 (SD 0·30) MJ/d; n 18) was not significantly different from the measured value (7·17 (SD 0·70) MJ/d; n 18). The range of DLW-derived expenditure values within the group was BMR X 1·41 to 2·41. The largest seasonal change within individuals was BMR X 0·5. The energy expenditure of the group as a whole was lower in winter (BMR X 1·88; SD 0·33; n 9) than summer (BMR X 2·01; SD 0·30; n 9) though the difference was not statistically significant. The average summer and winter DLW-derived expenditure was BMR X 1·96 (SD 0·31; n 17). The activity diary estimate of expenditure was BMR X 1·79 (SD 0·32; n 17). In a subset of the group who were representative of the most active 26% of all adult males in the UK, the DLW-derived expenditure was BMR X 2·08 (SD 0·24; n 11). This is higher than the highest Department of Health (1991) estimate of BMR X 1·6 for individuals in light occupations. The measured energy costs of low-intensity activities were similar to those presented in the Department of Health (1991) report but the value determined for running (BMR X 13·08; SD 2·4; n 6) was higher than the highest value in the report (BMR X 6 to 8). The results indicate that the recent Department of Health (1991) reference values for energy may underestimate the expenditure of a significant proportion of the UK population largely because the energy costs of activity used in the report to calculate expenditure do not accurately reflect those achieved during active leisure in individuals who take regular exercise.

Changes in tissue composition and protein synthesis ratio were studied in the major tissues of the body in young rats fed on lipid-rich, isonitrogenous purified liquid diets, a convenient method for inducing voluntary overfeeding under controlled nutritional conditions. Overfed rats showed faster growth induced by the energy excess. Analysis of tissue composition (protein, DNA and RNA contents) revealed that growth was due mainly to tissue hyperplasia in which protein and DNA contents increased in parallel. Fractional protein synthesis ratio measured in vivo by the flooding-dose method of phenylalanine showed a marked increase in all tissues. This change could be attributed to an increase in the ribosomal activity for protein synthesis in most tissues. Therefore, our results indicate that addition of a supplementary energy source (as lipids) to a well-balanced diet improves growth and protein synthesis in growing rats.

A modified mathematical model is described that simulates the dynamics of rumen micro-organisms, with specific emphasis on the rumen protozoa. The model is driven by continuous inputs of nutrients and consists of nineteen state variables, which represent the N, carbohydrate, fatty acid and microbial pools in the rumen. Several protozoal characteristics were represented in the model, including preference for utilization of starch and sugars compared with fibre, and of insoluble compared with soluble protein; engulfment and storage of starch; no utilization of NH3 to synthesize amino acids; engulfment and digestion of bacteria and protozoa; selective retention within the rumen; death and lysis related to nutrient availability. Comparisons between model predictions and experimental observations showed reasonable agreement for protozoal biomass in the rumen, but protozoal turnover time was not predicted well. Sensitivity analyses highlighted the need for more reliable estimates of bacterial engulfment rate, protozoal maintenance requirement, and death rate. Simulated protozoal biomass was increased rapidly in response to increases in dietary starch content, but further increases in starch content of a high-concentrate diet caused protozoal mass to decline. Increasing the sugar content of a concentrate diet, decreased protozoa, while moderate elevations of the sugar content on a roughage diet increased protozoal biomass. Simulated protozoal biomass did not change in response to variations in dietary neutral-detergent fibre (NDF) content. Reductions in dietary N resulted in an increased protozoal biomass. Depending on the basal intake level and dietary composition, protozoal concentration in the rumen was either increased or decreased by changes in feed intake level. Such changes in relative amounts of protozoal and bacterial biomass markedly affected the supply of nutrients available for absorption. The integration of protozoal, bacterial and dietary characteristics through mathematical representation provided an improved understanding of mechanisms of protozoal responses to changes in dietary inputs.