1. The influence of the nutrient composition of food on energy expenditure during a 24 h period was investigated in adult volunteers. The maximum probable effect was determined using iso-energetic diets high in either protein or in glucose.

2. Two men and four women took part in the study. Their body-weights and body composition were within the normal range. Each subject lived for 28 h in a whole-body calorimeterset at 26°, on two separate occasions. During each session they ate one of the following iso-energetic diets: high-protein–low-carbohydrate or high-glucose–low-protein.Energy expenditure was determined while the subject followed a pre-set pattern of activity. A 24 h collection of urine was made and total nitrogen, creatinine and urea excretions were determined, so that heat production could be corrected for protein metabolism.

3. Two independent measures of energy expenditure were made: direct calorimetry was used to obtain heat loss partitioned into its sensible and evaporative components, while indirect calorimetry was used to estimate heat production from oxygen consumption, carbon dioxide production and N excretion. There was good agreement between the two estimates of 24 h energy expenditure: for the twelve sessions in the calorimeter the mean difference between heat production and heat loss was only 0·4 (SEM 0·39)%.

4. The results showed that nutrient composition can have a marked influence on 24 h energy expenditure in adult humans. Mean values of 8659 (SEM 230) kJ and 7735 (SEM 250) kJ were obtained for the high-protein and high-glucose diets respectively. This 12% increasein energy expenditure on the high-protein intake was significant (P < 0·001). On the high-glucose intake, total heat loss comprised 22 and 78% evaporative and sensible heat losses respectively. The increase in heat loss onthe high-protein intake was accounted for by a 39% increase in evaporative heat loss and a 7% increase in sensible heat loss.

5. It is concluded that the composition of the nutrient intake has a greater influenceon the metabolic rate of adult humans than has been suggested by some groups of workers in recent years.

1. Iron availability in potatoes and ferrous sulphate was measured in rats in a 10 d balance study and from a single meal using 59Fe and 55Fe as extrinsic labels.

2. Dried potato samples were incubated in gastric juice in vitro and the amount solubilized was compared with other foods. The relationship between ascorbic acid content of dried potato and Fe solubilization was examined in vitro.

3. In the balance study, the rats absorbed (mean with SE) 15·2 (2·7)% Fe from the diet containing 660 g dried potato/kg and 32·1 (2·8)% Fe from the semi-synthetic diet containing FeSO4. Absorption was higher from the extrinsically-labelled single meal: 49·6 (1·1)% Fe from 59Fe-labelled potato and 62·4 (1·2)% Fe from 59FeSO4.

4. The in vitro experiments showed a much greater solubilization of Fe from potato than from the other foods examined. There was a correlation between Fe solubilization and ascorbic acid content of potatoes (rs 0·76, P < 0·00).

5. It appears that potatoes contain Fe of moderate availability, possibly higher than most vegetables. They also provide ascorbic acid which may enhance Fe absorption from a meal if present in sufficient quantities. Thus potatoes may make a useful contribution towards the Fe nutriture of the UK population.

1. In order to investigate the mechanism of the pellagragenic action of excess dietary leucine, rats were fed on diets providing a minimally-adequate amount of tryptophan, with no preformed niacin, with and without the addition of 15 g leucine/kg diet. This amount of leucine in the diet has been demonstrated previously to lead to depletion of blood and liver nicotinamide nucleotides. The metabolism of tryptophan was assessed by measurement of the production of 14CO2 after the administration of [methylene-14C]tryptophan to estimate the activity of kynureninase (L-kynurenine hydrolase, EC 3.7.1.3) and [benzene ring U-14C]tryptophan to estimate the activity of picolinate carboxylase (aminocarboxymuconate semialdehyde decarboxylase, EC 4.1.1.45).

2. A dietary excess of leucine led to inhibition of kynureninase and increased the activity of picolinate carboxylase. Both of these effects would result in a reduction in the rate of metabolism of acroleylaminofumarate (aminocarboxymuconate semialdehyde) to quinolinic acid and hence to nicotinamide nucleotides. These two effects provide an explanation for the pellagragenic effect of a dietary excess of leucine in animals that are wholly or partly reliant on endogenous synthesis from tryptophan to meet their requirements for nicotinamide nucleotides, and presumably also explain the pellagragenic effect of a dietary excess of leucine in man.

1. The effects of the administration of oestradiol and vitamin B6 on tryptophan metabolism in the rat have been assessed by measurement of the release of 14CO2 from [14C]tryptophan, in vivo, in order to determine whether, and to what extent, the abnormalities of tryptophan metabolism that are associated with oestrogen administration can be attributed to drug-induced vitamin B6 deficiency or depletion. Two positional isomers of [14C]tryptophan have been used; [ring-2-14C]tryptophan as an index of the activity of tryptophan oxygenase (L-tryptophan: oxygen oxidoreductase (decyclizing), EC 1.13.11.11) and [methylene-14C]trytophan as an index of the activity of kynureninase (L-kynurenine hydrolase, EC 3.7.1.3).

2. The administration of 500 μg oestradiol/kg body-weight led to a reduction in the release of 14CO2 from both positional isomers of tryptophan, suggesting that the activities of both tryptophan oxygenase and kynureninase are reduced following oestrogen treatment. The kinetics of the release of 14CO2 from [methylene-14C]tryptophan after the administration of oestradiol were compatible with competitive inhibition of kynureninase by oestradiol or a metabolite.

3. The administration of 10 mg pyridoxine hydrochloride/kg body-weight also reduced the production of 14CO2 from both positional isomers of 14C]tryptophan, suggesting some toxicity of such a high dose of the vitamin.

4. In animals which had received the supplementary dose of vitamin B6, the administration of oestradiol led to further reduction in the production of 14CO2 from [ring-2-14C]tryptophan, suggesting a further reduction in the activity of tryptophan oxygenase, and an increase in the production of 14CO2 from [methylen-14C]tryptophan, but with a delay in the peak of production.

5. These results confirm that there is no induction of tryptophan oxygenase by oestradiol, but rather reduced activity of the enzyme after the administration of a relatively high dose of the hormone. They also confirm that the inhibition of kynureninase by oestrogen metabolites that has been reported previously in partially-purified enzyme preparations also occurs in vivo.

6. It is suggested that the abnormal results of the tryptophan load test that have been reported in women receiving oestrogens, and which have been interpreted as indicating some extent of drug-induced vitamin B6 deficiency, can be accounted for by the inhibition of tryptophan metabolism by oestrogens or their metabolites. Therefore it seems likely that the practice of administering supplements of vitamin B6 to women receiving oestrogens may not be appropriate, and indeed may exacerbate the changes in tryptophan metabolism that result from the administration of oestrogens. The tryptophan load test would appear to be unreliable as an index of vitamin B6 nutritional status in women receiving oestrogens.

1. A triple stable-isotope method was used to estimat simultaneously selenium absorption from poultry meat intrinsically labelled with 74Se and from an extrinsic tracer of 76SeO32− in four young adult men. The subjects received an experimental diet based on chicken meat as the source of protein. Two diet periods, lasting from 5 to 10 d, depending on the frequency of stool output for each subject, were conducted to allow duplicate determinations within each subject of Se absorption from both sources.

2. Absorption of Se was determined by the faecal isotope balance procedure through monitoring the stable isotopes 74Se, 76Se and 80Se by means of radiochemical neutron activation analysis.

3. For the separate periods, mean (with SEM) absorption of 74Se from the intrinsically-labelled poultry meat was 70·9 (1·5)% and 72·0 (2·5)%. The absorption of Se from 76SeO32− was 34·7 (5·5)% and 37·6 (3·2)% during the same periods.

4. From these results it is concluded that, under the present experimental conditions, the intrinsic and extrinsic Se isotopes did not form a common pool before absorption. Possible reasons for this are discussed.

1. The potential use of an extrinsic label to measure iron absorption from a ferric orthophosphate-fortified malted cocoa drink was examined by measuring the solubility of the FePO4 in 0·1 M-hydrochloric acid.

2. The validity of using the stable isotope 58Fe as an extrinsic label was tested by comparing Fe absorption by rats from wheat flour extrinsically-labelled with 58Fe or 59Fe.

3. Fe absorption from a malted cocoa drink (20 g powder made up with hot water) fortified with FePO4 (0·5 mg Fe/g powder) was measured in human subjects using 58Fe as an extrinsic label. Absorption was calculated by measuring unabsorbed 58Fe in faeces. Absorptions of Fe from the drink fortified with either FePO4 or ferrous sulphate were compared. The effect of the addition of ascorbic acid to the drink (1 mg/g powder) on Fe availability was also examined.

4. The effect of fasting on Fe absorption from the drink was determined in rats by giving the drink to fasting animals or shortly after they had consumed a small meal.

5. The FePO4 was totally soluble in 0·1 M-HCl and there were no differences in absorption between 58Fe- and 59Fe-labelled wheat flour. In the human experiment the proportion of Fe absorbed from the drink plus FePO4 and ascorbic acid was (mean with SE) 0·25 (0·02), from the drink plus FePO4 0·24 (0·02) and from the drink plus FeSO4 0·23 (0·03). Fasting had a significant effect on Fe availability; rats given the drink shortly after a small meal absorbed less than half as much Fe as those given the drink on a fasted stomach.

6. It was concluded that the FePO4 used to fortify the malted cocoa drink was as well absorbed as FeSO4 but that the high levels of absorption were a reflection of the fasting condition of the subjects. The level of ascorbic acid was not great enough to enhance the availability of the FePO4 any further.

1. Twelve young adult male volunteers were given a low-fibre white bread diet (9 g neutral-detergent fibre (NDF)/d) and a medium-fibre coarse-bran bread diet (22 g NDF/d), each lasting 20 d. In a third period of 20 d the volunteers were subdivided in groups of four, consuming a high-fibre coarse-bran bread diet (35 g NDF/d), a medium-fibre fine-bran diet (22 g NDF/d, bran particle size > 0.35 mm) or a wholemeal bread diet (22 g NDF/d). Digestion of dietary fibre and its components hemicellulose, cellulose and lignin were determined as well as colonic function.

2. An increase of the amount of dietary fibre (through bran in bread) from 9 to 22 g NDF/d resulted in the following significant changes (P < 0.01): increase in faecal wet weight of 63 g/d, decrease in the percentage of faecal dry weight from 27 to 24, increase in defaecation frequency of 0.2 stools/d and reduction of the intestinal transit time of 36 h.

3. Further significant changes with regard to all factors mentioned were observed during the high-fibre diet. Faecal wet weight was significantly (P < 0.05) lower with the fine-bran bread diet than with the coarse-bran bread on a similar fibre intake of 22 g NDF/d. Results obtained in the wholemeal-bread period did not show significant differences compared with those from the coarse-bran bread period of 22 g NDF/d.

4. Mean digestibilities for the fibre from bread were: for NDF 0.34, for hemicellulose 0.46, for cellulose 0.20 and for lignin 0.04.

5. The results obtained suggest that the theory of sponge activity of the fibre matrix structure is the predominant factor accounting for the water binding capacity of fibre in the colon.

1. To evaluate the role of gestational protein-energy malnutrition on fetal hard-tissue growth and metabolism, we measured several variables in the growth centres of mandibles and long bones of newborn rats.

2. Control pups and pups of malnourished dams had approximately the same extent of reduction in body-weight, mandibular weight and long-bone weight.

3. The malnourished group had more cells in the mandible although cell size was the same as that of controls.

4. In contrast, in the long bones, the malnourished group had fewer cells than did controls whereas cell size was unchanged.

5. Calcium content was the same in long bones of both groups, but was less in the mandibles of pups from malnourished dams. Ca metabolism as measured by 45Ca uptake was unchanged in the long bones, but was increased in the mandibles of the malnourished group shortly after birth. Calcification patterns at birth in these bones correlated well with alkaline phosphatase (EC 3.1.3.1) activity.

6. These findings indicate that the mandibles and long bones of offspring are affected differently by protein–energy malnutrition during the mother's gestation. Prenatal nutritional stress resulted in a disturbance of the pituitary–adrenal system. Increased adrenal corticosterone could possibly be related to the different observed changes in bone metabolism.

1. Changes in concentrations of metabolites in blood and rumen fluid were measured in cows when fat and when thin and when given hay and concentrates at a restricted level or ad lib.

2. When fed ad lib., cows consumed 24% more food when thin than when fat.

3. Concentrations in rumen fluid of acetate and propionate after feeding at both levels did not differ significantly between fat and thin cows.

4. Concentrations in blood of the lipogenic substrates acetate and 3-hydroxybutyrate did not differ between fat and thin cows after feeding, but glucose concentration fell more rapidly in thin cows especially when fed ad lib. Propionate rose more in thin cows than in fat cows when fed ad lib. Non-esterified fatty acids were higher in fat cows before feeding, but fell to similar levels to those in thin cows after feeding.

5. The results are interpreted as indicating a more rapid rate of fatty acid synthesis in adipose tissue of thin cows. This in turn tends to lower blood levels of fatty acid precursors and so enhance the rate of their absorption from the rumen. This in turn permits higher intake of food before short-term chemical regulators of intake start to operate.

1. Various methods of estimating intestinal mass and cell proliferation were used to compare the effects of a pelleted laboratory diet (diet A), an elemental diet (Flexical; diet B), Flexical plus kaolin (diet C) and Flexical plus cellulose (diet D) on the mucosa and other tissues of the mouse small intestine and colon.

2. The weight of the distal third of the small intestine was significantly decreased in mice given diets B, C and D (P < 0·001). The length of the colon was significantly decreased in the mice given diets B (P < 0·001), C (P < 0·01) and D (P < 0·05); however, the weight of the colon was only decreased in the mice given diet B or diet C (P < 0·001).

Similar changes were noted in the weights of the intestinal muscle and serosa layers; however, no such changes were noted in the weight or DNA content of the mucosa.

3. No changes were observed in the crypt cell production rate in the small intestine, apart from an increase in the mid-region (P < 0·01) of mice given diet C, which was associated with a similar increase in the mucosal content of DNA.

Crypt-cell production was significantly decreased (P < 0·01, 0·001) in the two sites of the colon studied in the mice given diets B or C, but the crypt-cell production rates were not significantly different from control levels at either site in the mice given diet D.

4. The length of the colonic crypts was significantly decreased (P < 0·05, 0·02) in mice given diets B and C, but not in those given diet D; total cell number showed a similar change (P < 0·01, 0·05).

The correlation coefficient between the length of the colonic crypts and absolute cell number was 0·513.

5. The conclusion of the present study was that dietary fibre (cellulose), but not inert bulk (kaolin), prevents mucosal atrophy of the colon of mice given a fibre-free diet, and that many of the observed changes in intestinal weight are due to reduction in the bulk of the muscle layer.

1. Two dairy cows were maintained by intragastric infusion of volatile fatty acids and casein. Except when fasting, the casein-nitrogen was held constant, while total gross energy supply was varied from zero during fasting to 650 kJ/kg body-weight (W)0·75.

2. One cow was estimated to attain zero N balance at an energy intake of 255 kJ/kg W0·75 and the other at 307 kJ/kg W0·75, which was calculated to be substantially below the estimated energy required for zero energy balance.

3. When the cows were later given an N-free infusion for a period preceding the trial, N balance occurred at 98 kJ/kg W0·75 for one cow and 115 kJ/kg W0·75 for the other.

4. Four steers were similarly nourished by intragastric infusion and the energy nutrient increased from 0 at fasting to 450 kJ/kg W0·75. The protein was held constant at 1 g N/kg W0·75 except at fasting. The energy level at which N balance occurred was 154 (SE 38) kJ/kg W0·75 or approximately equal to the energy content of the protein. The practical implications of these findings are discussed.

1. The effect of xylitol feeding on the iron content of rat tissues was studied.

2. Adult male rats were fed on the basal diet containing (g/kg) 200 glucose, or 50 or 200 xylitol, or the same diet containing no added carbohydrates for 8 weeks. Each feeding group comprised nine animals.

3. Xylitol at 200 g/kg diet retarded the growth rate of the rats, whereas 200 g glucose/kg increased the weight gains compared with animals given no added carbohydrates.

4. Xylitol at 50 g/kg did not affect the tissue Fe concentrations, but 200 g xylitol/kg increased the Fe content of the livers, duodenum wall, spleen, bone marrow and serum.

5. Cadmium and lead contents of the livers were similar in all groups.

6. Xylitol–Fe complexes are suggested to be responsible for the increased Fe absorption during xylitol feeding.

1. The absorption of 64Cu from closed duodeno-jejunal loops in anaesthetized rats was significantly less in the presence of pancreatic juice compared with that in the presence of saline (9 g sodium chloride/1). The inhibition of 64Cu absorption caused by pancreatic juice was similar to that achieved with bile.

2. Studies using solutions of electrolytes and of pancreatic extracts showed that the inhibitory effect of pancreatic secretions was due to its protein-enzyme content and not to its bicarbonate content.

Pancreatic secretion and bile influence Cu absorption and thereby affect Cu homeostasis.

1. For a period of 8 weeks, rainbow trout (Salmo gairdneri), mean initial weight 21 g, were given either a low-magnesium or control diet containing 0·03 and 0·58 g Mg/kg diet respectively. Both groups of trout were then given the control diet for a further 11 weeks.

2. Weight gains over the initial 8-week period were lowest in the Mg-deficient trout. Feeding the deficient fish the control diet rapidly improved growth rate until it was the same as that of the control trout.

3. Plasma Mg was significantly lower in the Mg-deficient trout at week 8. Feeding with the control diet for 11 weeks did not increase plasma Mg. Few changes were observed in the plasma concentrations of the other electrolytes.

4. Renal calcium concentrations were unaffected by dietary Mg levels. Similarly, the renal levels of phosphorus, sodium and potassium all fell within the range found in normal rainbow trout.

5. Muscle Mg concentrations were reduced in those trout given the Mg-deficient diet. Feeding with the control diet for a further 11 weeks increased muscle Mg but the level was still significantly lower than that found in trout given the control diet for 19 weeks.

6. The bone ash Mg concentration was significantly lower, and the Ca higher, in the deficient fish at week 8, when compared with the control group.

7. When compared with the value at the start of the experiment, total bone Mg fell slightly in the deficient trout over the initial 8-week period, but increased in the control group of fish. Feeding with the control diet for a further 11 weeks increased total bone Mg in both Mg-deficient trout and control trout.

8. The results show that the Mg deficiency imposed on the rainbow trout was of limited severity and almost complete recovery was obtained when the control diet was fed.

1. [125I]iodoinsulin-binding studies in the presence of a concentration range of bovine insulin were conducted to establish specific insulin-binding levels in skeletal muscle plasma membranes and isolated hepatocytes of rainbow trout (Salmo gairdneri) reared on control, high-protein or high-carbohydrate diets.

2. Negative co-operativity was observed and receptor concentrations and apparent dissociation constants established for each preparation.

3. No differences of specific binding attributed to diet were detected in skeletal muscle plasma membrane preparations; however, the receptor concentration of isolated hepatocytes from high-carbohydrate-reared trout was increased. This contrasted to comparable mammalian studies.

1. Emulsions of C18 unsaturated fatty acids (FA) were infused for 2 h into the intestine of conscious sheep while motility of the reticulum and rumen was recorded.

2. Statistically-significant depression of motility was found when 3 or 5 g FA/h were infused. At 1 g/h there were minor disruptions of motility.

3. The inhibitory potency was not related to the extent of unsaturation of the FA.

4. Receptors mediating the inhibitory effect were postulated to be distal to the iliac flexure of the duodenum, but the possible role of bile and pancreatic juice is discussed in relation to this problem.

5. The probability that the effect was hormonally mediated is discussed.

1. Clun Forest ewes with single and twin lambs were exposed to neutral (20°) or cold (−1°) environmental temperatures, beginning soon after parturition, for 4 d. The intakes of milk, lactose and glycerides by the lambs were calculated from measurements of the rate of displacement of tritiated water (injected into the lambs) by non-radioactive water in milk from the ewes, and measurements of the concentration of lactose and glyceride glycerol in small samples of milk.

2. The yield of milk from ewes bearing twin lambs was greater than the yield from single-bearing ewes in the neutral environment but, in both environments, twin lambs had lower intakes of milk and milk lactose and glycerides, and gained body-weight more slowly, than single lambs. Milk from twin-bearing ewes had a lower lactose concentration than milk from single-bearing ewes.

3. Cold exposure reduced the intake of milk and milk lactose, and reduced the rate of weight gain, of single and twin lambs. Glyceride intake was not different in the two environments.

4. There appears to be a conflict between reduced supply of milk by the ewe and increased demand for milk by the lamb in cold temperatures. Such a conflict is sharpened when twin lambs are born.

1. The fractional rates of loss of 14C and body-weight were measured in growing female rats after a single dose of [1-14C]methionine. After the dose, the rats were maintained for 30 d on diets containing graded amounts of methionine and killed at 30 d.

2. By 20 d after the dose the level of labelling of body proteins was fairly uniform. From 20 to 30 d, 14CO2 was collected at intervals. The rats were killed at 30 d and the total radioactivity remaining in the body was measured.

3. The fractional loss of 14CO2 between days 20 and 30 was constant regardless of methionine intake except at the highest intake level.

4. After correcting the fractional loss of 14CO2 for urinary 14C loss, a value of 35 mg/kg body-weight (20 mg/kg body-weight0·75) was obtained for the rate of endogenous methionine oxidation.

1. The loss of body water of eight sows in the 7 d following weaning was determined using the deuterium oxide dilution technique. Four of the sows had received a concentrate diet in restricted amounts while the other four had been given the same diet mixed with two-thirds its weight of oat husks ad lib. during the whole of the preceding lactation. Certain blood and urine constituents were also measured.

2. Loss of body water was significantly less (P < 0·05) than weight loss of fasted animals, but body water losses were considerable in six of the eight animals.

3. Excretion of urinary nitrogen, urea and creatinine and levels of plasma urea were higher, while levels of plasma non-esterified fatty acids and the hydroxyproline index were lower 1 week after weaning compared with values obtained on the day following weaning.

4. These results indicate that in addition to water loss, depletion of body tissue, including protein, occurs in the newly-weaned sow.