1. Anthropometric indices are presented for representative samples of elderly people in South Wales, based on over 1500 subjects seen during community surveys.

2. Body mass index declined with age after 70 years in both men and women. Estimates of fat and muscle volume based on upper arm measurements also showed a decline with age, which was particularly steep for triceps skinfold thickness in women.

3. These indices are in general similar to results that have been reported from other surveys within the UK; they suggest that Welsh old people have less fat and muscle than elderly Americans.

1. Protein utilization in young men under circumstances of one or two periods of work and both adequate and surfeit energy intake was determined by nitrogen balance; protein intake was constant at the FAO/WHO (1973) safe level (0.57 g/kg body–weight).

2. Physical activity affected protein utilization negatively by increasing sweat and faecal N losses, and positively by supporting increased energy intake.

3. Efficiency with which surfeit energy improved N utilization (mg N retained/added kJ) was greater under circumstances of increased activity.

4. Changes in body composition as determined by total body potassium and hydrostatic weighing supported the N retention values.

1. Iron retention and its subsequent distribution from 3 g 59Fe extrinsically-labelled wholewheat flour in rats given a low (8 μg Fe/g)- or high (566 μg Fe/g)-Fe diet during the previous 3 d was measured (Expt 1). The mean (with se) proportion of Fe retained from wholewheat flour was 0.46 (0.04) in the group given the low-Fe diet and 0.15 (0.01) in the group given the high-Fe diet (P < 0.001). There was no difference in distribution of absorbed 59Fe in the tissues examined.

2. The procedure was repeated in rats given diets containing a range of Fe concentrations, groups 1–6 respectively: 8, 77, 136, 334, 566, 1270 μg Fe/g (Expt 2). The mean (with se) proportions of Fe retained in groups 1–6 respectively were 0.60 (0.02), 0.34 (0.02), 0.30 (0.02), 0.20 (0.20), 0.17 (0.02), 0.09 (0.01). Regression analysis showed that Fe retention was a function of the logarithm of the Fe concentration of the diet consumed before the test meal (R -0.997, P < 0.0001) where Fe retained (μg) = 95–28 log10 Fe concentration of diet.

3. Rats were given a low-, medium- or high-Fe diet (8, 136 or 1270 μg Fe/g respectively) for 1 or 2 d instead of 3 d before measuring Fe retention from 3 g wholewheat flour (Expt 3). The mean (with se) proportions of Fe retained in rats given the low-, medium- or high-Fe diets for I d were 0.45 (0.02), 0.25 (0.02) and 0.13 (0.01) (P < 0.001) and for 2 d 0.47 (0.03), 0.31 (0.03) and 0.18 (0.02) (P < 0.001). There were no significant differences in Fe retention from animals given similar diets for 1 or 2 d before the test meal. As in Expt 2 regression analysis showed a highly-significant relationship between Fe retention and the logarithm of the previous dietary Fe concentration in both sets of groups.

4. It was concluded that the amount of Fe retained by rats from a 3 g meal of wholewheat flour depended on the previous dietary Fe intake. Only one meal in the previous 24 h was required to influence the ‘mucosal setting’ since there was no difference in response between rats preloaded for 1 or 2 d before the test meal.

1. The contribution of the fortification of flour with calcium carbonate to the Ca intake of 375, 11–14-year-old Northumbrian children has been calculated.

2. Mean Ca intakes were above those currently recommended for children of this age. The fortification of flour supplied 16% of the total Ca intakes.

3. Without the fortification, the percentage of these children with intakes below the recommended intake would be more than double. This would include the majority of girls (particularly those of social classes III, IV and V).

4. The recommendation to stop fortifying flour with calcium carbonate should be reviewed.

1. A new method has been developed for the study of zinc metabolism in man using the stable isotope 67Zn. The technique involves intravenous infusion of the isotope followed by measurements of the plasma and faecal enrichments over a period of days.

2. A procedure for the analysis of Zn isotopes in plasma and faeces is described which requires the separation of Zn from other elements using the chelator dithizone before analysis by thermal-ionization mass spectrometry.

3. The stable isotope technique has been used in conjunction with a metabolic balance study to obtain measurements of Zn absorption and gastrointestinal secretion in a normal subject. Preliminary measurements of the size of the exchangeable pool of Zn have been made as have estimates of the rates of plasma and whole-body Zn turnover.

4. Following an increase in dietary Zn the body appeared to respond in two ways. The gastrointestinal secretion of Zn increased immediately, but only by a relatively small amount. The absorption of Zn initially increased in proportion to the increase in dietary levels but then decreased within 4 d by an amount sufficient to restore Zn balance.

1. Peripheral blood leucocytes from human male volunteers and from male rats were incubated in vitro in the presence of 14C-labelled linoleic acid ([14C]LA) or 3H-labelled arachidonic acid ([3H]AA). The time-course of [14C]LA and [3H]AA incorporation into human leucocyte total lipids was maximal at 80–90% of the initial dose within 20–30 min of dosing the cells.

2. Compared with mixed leucocytes, isolated polymorphonuclear leucocytes were only marginally different in the differential incorporation of [14C]LA and [3H]AA into total lipids.

3. In human leucocytes, [14C]LA was incorporated initially into triglycerides but predominantly into phosphatidylcholine thereafter. In the rat, [14C]LA remained as the free acid (63%), with lesser amounts entering the phospholipids (9%), monoglycerides-diglycerides (12%) and triglycerides (< 1%).

4. Utilization of [14C]LA by the Δ6-desaturase was only a minor route of its metabolism in both human and rat leucocytes.

5. 3H-labelled prostaglandins E2 and F2α accounted for up to 30% of the radioactivity released into the incubation medium from human leucocytes incubated with [3H]AA for 60 min.

6. Stimulation of phagocytosis in the human leucocytes with latex beads or with unopsonized zymosan did not alter the differential incorporation of [14C]LA or [3H]AA into the leucocyte lipid fractions.

1. The effect of the administration of oestrone sulphate on tryptophan metabolism has been assessed in rats in order to determine whether and to what extent inhibition of tryptophan metabolism by oestrogens may be a factor in the aetiology of pellagra, and might explain the reported twofold excess of females over males in many outbreaks of pellagra.

2. Feeding ovariectomized rats for 1 week on a diet containing 15 mg oestrone sulphate/kg led to significant inhibition of kynurenine hydroxylase (EC 1.14.13.9), kynureninase (EC 3.7.1.3) and 3-hydroxyanthranilate oxidase (EC 1.13.11.6). There was also a significant increase in plasma tryptophan, suggesting decreased activity of tryptophan oxygenase (EC 1.13.11.11). This inhibition of tryptophan metabolism will result in a considerable reduction in the synthesis of the nicotinamide nucleotide coenzymes (NAD and NADP) from tryptophan.

3. When ovariectomized rats were maintained for 4 weeks on a diet providing no preformed niacin and only a marginally adequate amount of tryptophan (1030 mg/kg), the addition of oestrone sulphate to the diet led to a significant reduction in the liver content of nicotinamide nucleotides and the urinary excretion of the end-product of NAD metabolism, N1-methyl nicotinamide.

4. It is suggested that when the diet is only marginally adequate in tryptophan and niacin, inhibition of tryptophan metabolism by endogenous or administered oestrogens may be an additional factor in the development of pellagra.

1. The energy metabolism of young pigs offered low-protein diets to appetite or a normal starter (diet 1, 225 g crude protein (nitrogen x 6·25; CP)/kg dry matter (DM)) to maintain zero energy balance was studied using indirect calorimetry and slaughter. The treatments were: T1, diet 1; T2, 46 g CP/kg DM; T3, 21 g CP/kg DM; T4, 17 g CP/kg DM; T5, 21 g CP/kg DM and no supplemental thiamin.

2. Daily heat production (kJ/d per kg body-weight (W)0·75) declined on all treatments from a pre-experimental value of 613. The greatest decline was observed in T1 pigs where the final value was 375.

3. There was a progressive reduction in energy intake from 5·4 MJ/d for T2 pigs to 3·0 MJ/d for T4 and T5 pigs (P < 0·001). The mean intake of T1 pigs was 2·3 MJ/d.

4. There were highly significant treatment differences (P < 0·001) in gain of live-weight and in the gain of carcass DM, CP, fat and energy.

5. There were marked treatment effects on body composition. T1 pigs showed a decrease in the proportion of carcass fat and an increase in the proportion of carcass CP during the experiment while the other four treatments caused large increases (P < 0·001) in carcass DM and fat content and no change in CP content. These changes resulted in large differences in the energy content of the gain, the mean values (MJ/kg) being 0·6, 35·5 and 88 for T1, T2 and T3 pigs respectively. T4 and T5 caused energy gain coupled with weight loss.

6. A linear regression of energy retention (ER; MJ/d per kg W0·75) on metabolizable energy (ME) intake yielded the equation

ER = 0·78 ME-0·365, r0·96.

7. These results indicate that heat production declines when the growth rate of young pigs is reduced either by restriction of energy or of protein intake. They do not support the suggestion that low-protein diets give rise to increased ‘diet-induced’ thermogenesis.

1. Protein utilization was determined by assay with low-protein diets limiting in one of nine essential amino acids. The diets contained 50 g protein/kg and the amino acid score of the protein was 0.50.

2. Protein utilization was found to be related to the particular limiting essential amino acids present.

3. The usefulness of Bender's (1965) standard amino acid requirement for the estimation of amino acid utilization from a low-protein diet is discussed.

1. Retinol esterification in the small intestine, liver and kidney of rats given a normal diet or a vitamin-A-free diet and of rats given large doses of vitamin A was studied. The active enzyme is a microsomal acyl CoA: retinol acyl transferase (ARAT).

2. In the small intestine ARAT activity was 0.37 nmol ester/mg microsomal protein per min. Large doses of vitamin A increased the activity significantly, while the enzyme activity in the vitamin-A-deficient rats was in the range of that of the controls. Retinoic acid in physiological doses (0.064 mg three times per week) had no influence on ARAT activity.

3. In the liver, ARAT activity of the controls was 0.58 nmol ester/mg microsomal protein per min. The activity was increased after large doses of vitamin A. It was not significantly reduced in vitamin-A-deficient animals.

4. The kidney had a low, but significant ARAT activity, both in normal and vitamin-A-deficient animals and after large doses of vitamin A (range 0.08–0.14 nmol ester/mg microsomal protein per min).

5. The vitamin-A-esterifying enzyme in the small intestine and liver of the rat seems to be influenced by the amount of retinol in the diet.

1. The present study was done to clarify the relationship between the amount of dietary protein given to, and the gut microflora of, the host. Day-old chicks were given diets containing three concentrations of dietary protein (50, 200 and 400 g/kg) for 14 d. Body-weight gain, food consumption, body consumption, and protein and energy utilization were measured.

2. There was no difference in body-weight gain and food consumption between germ-free (GF) and conventional (CV) chicks, but food conversion efficiency (g body-weight gained/g food consumed) was significantly higher in GF than in CV chicks.

3. Little difference was found in protein retention (g protein retained/14 d), but protein retention rate (g protein retained/g protein consumed) tended to be higher in GF chicks, particularly those given the diet with the lowest protein.

4. The presence of micro-organisms improved metabolizable energy (ME) values of the diets, but not all of the digested energy in CV chicks was utilized for growth. Therefore there was little difference in energy retention (kJ energy retained/14 d) between environments, although energy retention rate (kJ energy retained/kJ ME consumed) was significantly lower in CV chicks. The amount of body fat in GF chicks was higher than that in CV chicks, especially in those fed on the low-protein diet.

5. It is suggested that although the gut microflora may have beneficial effects on the digestion of dietary energy components, they may have detrimental effects on utilization of ME by their hosts, because chicks harbouring a gut microflora seem to have higher energy requirements for maintenance.

1. Volatile fatty acids (VFA) absorption in the large intestine of the anaesthetized rabbit was evaluated by measuring variations in the concentration of VFA in intestinal loops and plasma arteriovenous differences. Metabolic conversions were studied using [1-14C]acetate, [1-14C]propionate and [3,4-14C]butyrate.

2. The hind-gut tissues metabolized the three VFA, although this metabolism varied with the segment studied. Butyrate was the best respiratory fuel for the colonic wall, followed by propionate; acetate participated also, but it was mainly converted to glutamate.

3. The liver was the main organ metabolizing absorbed propionate and butyrate; acetate was available for extrahepatic tissue metabolism.

4. For the rabbit, VFA represented about 40% of the maintenance energy requirement.

1. Groups of rainbow trout (Salmo gairdneri) (mean weight 14 g) were given diets containing 0.8, 1.3, 2, 3, 4 or 6 g tryptophan/kg diet for 12 weeks.

2. By analysis of the growth results, the dietary requirement of tryptophan was found to be 2.5 g/kg diet (equivalent to 50 mg/kg biomass per d).

3. Carbon dioxide expired by trout following intraperitoneal injection of [14COOH]tryptophan contained little radioactivity when dietary tryptophan level was low but, above 2.0 g/kg diet, it increased rapidly with increasing dietary tryptophan level. The break point in the dose-response curve did not, however, coincide with that from the growth results.

4. Changes in concentrations of free tryptophan in blood and liver and activity of hepatic tryptophan pyrrolase (EC 1.13.11.11) in response to changes in dietary tryptophan concentration did not provide reliable indicators for quantifying dietary requirement. Unlike the situation in mammals, blood tryptophan was not protein-bound to any appreciable extent. Tryptophan pyrrolase of trout has properties which suggest it has no apoenzyme form.

5. In fish given adequate levels of tryptophan injected intraperitoneally with a tracer dose of [14COOH]tryptophan, 60% of the dose was incorporated into body protein within 1 d. The turnover of the label in this protein is very slow.

6. Those trout given diets deficient in tryptophan suffered from severe scoliosis and lordosis as well as having increased liver and kidney levels of calcium, magnesium, sodium and potassium.

1. Effects of sodium hydroxide treatment on intake and digestion of straw organic matter (OM), and microbial protein synthesis were examined in comparison with untreated and treated straws.

2. Intakes (kg dry matter (DM)/d) of untreated, NaOH- and sodium carbonate-treated straws were 5.21, 7.04 and 6.48 respectively and intakes (kg/d) of digestible organic matter (DOM) for the respective diets were 2.57, 3.73 and 2.98 respectively. NaOH-treated straw ranked higher than untreated straw in intakes of DM and DOM (P < 0.01).

3. The proportion of DOM intake that was apparently digested in the rumen was 0.74, 0.77 and 0.66 on untreated, NaOH- and Na2CO3-treated straws respectively.

4. Although the amount of bacterial N leaving the abomasum was higher with NaOH-treated than with untreated straw (74.6 v. 56.8 g/d, P < 0.01), efficiencies of bacterial N synthesis were not different between these treatments (28.6 v. 31.5 g bacterial N/kg OM apparently digested, P > 0.05).

5. The live-weight gain which the NaOH-treated straw could support was predicted to be 350 g/d and it was concluded that a protein supplement would have provided further increase in production in diets based on NaOH-treated straw.

1. The effect of body fatness on the fasting heat production and energetic efficiency of adult sheep was studied.

2. Energy balance and heat production were determined in adult wether sheep at three fatness levels given a diet of grass hay and maize at four feeding levels, including fasting, in open-circuit respiration chambers. The sheep weighed approximately 60 kg at the start and were fed over a period of 4–7 months to obtain one of three levels of bodyfatness: fat 90 kg, medium 70 kg and thin 55 kg.

3. Neither the digestibility nor the metabolizability of the diet was affected by body fatness or feeding level.

4. Average fasting heat production was 6.47, 7.00 and 8.20 MJ/d for the thin, medium and fat sheep respectively, but when expressed as a multiple of metabolic body size (kg W0.75) remained constant at 0.31 MJ/kg W0.75.

5. At each level of feeding the fat sheep produced most heat, but when heat production was expressed as a multiple of fasting heat production or metabolic body size, the differences due to level of fatness disappeared. Heat increment was not affected by fatness and there was no suggestion that energy utilization was improved by loss of condition.

6. It is concluded that white adipose tissue is highly active and contributes significantly to the maintenance energy requirements of adult sheep. Metabolic body size is a good unit of reference for comparison of energy metabolism in adult animals of the same species but varying in body size.

1. Two nitrogen-balance experiments were performed with growing rats to test the effect of dietary fibre level, protein quality and antibiotic inclusion on microbial activity, N excretion patterns and energy digestibility. Each experiment involved eight dietary treatments in a 2 x 2 x 2 factorial design, with five rats per treatment. The eight treatments resulted from a combination of two protein treatments, two fibre treatments and two antibiotic treatments. In Expt 1 the protein was provided as barley, or barley plus 2 g L-lysine hydrochloride/kg dry matter (DM) (at 15 g N/kg DM) and in Expt 2 as soya-bean meal or soya-bean meal plus 2 g DL-methionine/kg DM (at 15 g N/kg DM). In both experiments the basal diet was provided with or without additional fibre as 100 g barley husk/kg DM and with or without antibiotic as 7 g Nebacitin/kg DM.

2. With both barley and soya-bean meal, true protein digestibility (TD) was improved with the addition of amino acids. Only with the soya-bean meal diets was TD increased with Nebacitin treatment, with the effect of Nebacitin and methionine being additive. Barley husk slightly reduced the TD of soya-bean meal.

3. The effect of treatments on biological value (BV) was considerable. Lysine increased BV of the barley diet from 0.741 to 0.815 whereas Nebacitin reduced BV from 0.799 to 0.757. Methionine increased the BV of soya-bean meal from 0.754 to 0.911 while BV was reduced by Nebacitin from 0.843 to 0.821 and by barley husk from 0.845 to 0.820.

4. Net protein utilization (NPU) was markedly improved by the addition of amino acids and reduced by the addition of Nebacitin. Barley husk reduced NPU with soya-bean meal diets only.

5. Amino acid addition had no effect on energy digestibility of either diet, but Nebacitin reduced this value by approximately 5% on the barley diets, with a smaller reduction on the soya-bean meal diets. Fibre reduced energy digestibility of both diets.

6. On both diets, blood urea (BU) decreased with addition of amino acids. Nebacitin increased BU with the barley diets, but decreased BU with the soya-bean meal diets. With the soya-bean meal diets, the decrease with a combination of barley husk and methionine was particularly marked.

7. Microbial activity, as measured by caecal ATP activity, was strongly reduced by antibiotic addition with both protein sources. On the soya-bean meal diets ATP activity was increased by the addition of methionine.

8. The results demonstrated a difference in response to the addition of fibre and the first limiting amino acid to barley and soya-bean meal, as measured by several indicators of protein and energy utilization.