Trends in global fish catches are described together with fish landlings and fish consumption in the UK. The importance of n–6 and n–3 polyunsaturated fatty acids as essential constituents of human diets is considered and the role of oily fish as a dietary source of the long-chain n–3 polyunsaturates, docosahexaenoic acid and eicosapentaenoic acid, is emphasized. The origin ofn–3 polyunsaturates in the marine phytoplankton and their transmission via zooplankton to fish is described as a means of understanding the consumption of different fish body oils. The ease with which the fatty acid composition of fish body oils can be manipulated by altering the fatty acid composition of their feeds is emphasized and the dietary requirements of marine and freshwater fish for n–3 and n–6 polyunsaturates considered. Farming fish on diets containing principally fish meal and fish oil, as used in salmon production in Scotland, generates a high quality product with levels of long-chain n–3 polyunsaturates equalling or exceeding those of wild fish. Farming fish on high quality marine oils rich in docosahexaenoic and eicosapentaenoic acids is an efficient means of delivering these essential nutrients in human diets and also efficiently exploiting a strictly limited marine bioresource.

Fat digestion and metabolism differ widely between animal species. In ruminants, dietary fats are hydrogenated in the rumen before intestinal absorption so that absorbed fatty acids (FA) are more saturated than dietary FA. In non-ruminants, intestinal FA digestibility depends on the level of saturation of dietary FA. Fat supplementation of the diet of cows decreases milk protein and has a variable effect on milk fat, depending on the source of dietary lipids. When encapsulated lipids are used, the linoleic acid content of milk is increased, but the organoleptic quality of milk may be altered. Supplementary lipids are incorporated into non-ruminant body fat, whereas de novo lipogenesis is reduced. There is a close relationship between the nature of dietary FA and non-ruminant body FA.

The predominant fatty acids in milk are the long-chain fatty acids myristic, palmitic and stearic. These saturated fatty acids account for 75 % of the total fatty acids, with a further 21 % occurring as monounsaturated fatty acids of which the most prevalent is oleic acid. Only 4 g/lOO g of the milk fatty acids are polyunsaturated, occurring mainly as linoleic and linolenic acids. All milk fatty acids are derived, almost equally, from either de novo synthesis or directly from preformed fatty acids in the diet. There are four main dietary sources of fatty acids: forages, oilseeds, fish oil and fat supplements. The digestive tract exerts a profound influence on the fate of dietary fatty acids. The short-chain saturated free fatty acids are absorbed through the walls of the rumen or abomasum into the bloodstream. The medium- and longer-chain saturated fatty acids pass into the small intestine, diffuse across the membrane wall where they are incorporated into lipoproteins and enter the bloodstream via the lymphatic system. The majority of unsaturated fatty acids are extensively hydrogenated in the rumen. However, recent work has shown that the levels of certain saturated fatty acids can be reduced and the levels of oleic, linoleic and linolenic fatty acids increased by feeding oilseeds rich in mono- or polyunsaturated fatty acids. In addition, work reported here has confirmed that eicosapentaenoic and docosahexaenoic acids can be transferred to milk when a diet containing fish oil is fed, but the transfer efficiencies are low

Meat has been identified, often wrongly, as a food having a high fat content and an undesirable balance of fatty acids. In fact lean meat is very low in fat (20–50g/kg), pork and poultry have a favourable balance between polyunsaturated and saturated fatty acids (P:S) and grazing ruminants produce muscle with a desirable n–6:n–3 polyunsaturated fatty acid ratio. In all species, meat fatty acid composition can be changed via the diet, more easily in single-stomached pigs and poultry where the linoleic, α-linolenic and long-chain polyunsaturated fatty acid content responds quickly to raised dietary concentrations. Recent work in pigs has attempted to manipulate the n–6:n–3 ratio by feeding higher levels of α-linolenic acid (e.g. in rapeseed) or its products eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6) present in fish oils. In ruminants the challenge is to increase the P:S ratio whilst retaining values for n–6: n–3 found in cattle and sheep fed on forage diets. The saturating effect of the rumen can be overcome by feeding polyunsaturated fatty acids which are protected either chemically, by processing, or naturally e.g. within the seed coat. Some protection occurs when grain-based or grass-based diets are fed normally, leading to relatively more n–6 or n–3 fatty acids respectively. These produce different flavours in cooked meat due to the different oxidative changes occurring during storage and cooking. In pigs and poultry, high n–3 fatty acid concentrations in meat are associated with fishy flavours whose development can be prevented with high dietary (supranutritional) levels of the antioxidant vitamin E. In ruminants, supranutritional vitamin E delays the oxidative change of oxymyoglobin to brown metmyoglobin and may also influence the characteristic flavours of beef and lamb.

The nutritional manipulation of the diets of laying hens to include sources of n–3 fatty acids promotes the deposition of these nutrients into egg yolk. n–3 Fatty acid-rich eggs may provide an exciting alternative food source for enhancing consumer intake of these proposed healthful fatty acids. Care must be taken when designing n–3 fatty acid-rich poultry rations, however, to assure that the resulting egg fatty acid profile is useful for promoting consumer health yet maintaining egg sensory quality. In study 1 laying hens were fed on diets supplemented with graded levels of menhaden oil (MO), rich in both eicosapentaenoic acid (EPA; 20:5n–3) and docosahexaenoic acid (DHA; 22: 6n–3), for 4 weeks to determine maximal yolk fatty acid deposition attainable without sensory compromise. Yolk fatty acids were analysed for an additional 4 weeks, post-MO removal, to investigate yolk n–3 fatty acid tenacity. Dietary MO levels between 15 and 30g/kg yielded the greatest yolk n–3 fatty acid content; however, only eggs from birds fed with 15g MO/kg were considered acceptable by trained flavour panelists. Evaluation of eggs from hens fed with 15g MO/kg during storage verified that the shelf-life of enriched eggs was comparable with that of typical eggs. In study 2, graded levels of whole or ground flaxseed were used for the deposition of linolenic acid (LNA; 18:3n–3) and to determine in vivo production of DHA from dietary LNA for yolk deposition. Flaxseed form influenced yolk n–3 fatty acids only when given at 150 g/kg diet. In vivo production of DHA, while significant, was not enhanced by increasing the level of dietary flaxseed nor by grinding the seed. In the third study, a DHA-rich natural marine alga (MA) was investigated as an n–3 fatty acid supplement. Despite similar DHA profiles, dietary MA was found to be more efficient for yolk DHA deposition than dietary MO. These studies suggest that there are numerous viable n–3 fatty acid supplements for poultry rations. It must be realized, however, that the fatty acid profile of the final product varies substantially depending on which supplement is fed.

The dietary customs of people of South Asian origin living in Britain are important determinants of health but have been relatively little studied. As part of the Coventry study of diabetes carried out in the Foleshill ward of the city, subjects undergoing oral glucose tolerance tests provided information on this aspect of lifestyle. A questionnaire was completed by all of the last 612 subjects undergoing testing. These included 304 of European origin, 118 Punjabi Sikhs, seventy-six Pakistani/Punjabi Moslems, twenty-eight Gujerati Moslems, twenty-five Punjabi Hindus and forty-seven Gujerati Hindus. There were no discernible differences in the dietary customs of those with normal glucose tolerance, impaired glucose tolerance and newly diagnosed diabetes. Subjects of South Asian origin ate significantly fewer meals per day than European subjects. Evening meal times were 2–3 h later among South Asians. Europeans ate less fruit but more vegetables and more brown rice than South Asians. Gujeratis ate more rice, fried snacks and white flour. Moslems were least likely to be vegetarians, to drink alcohol and to use home-made ghee and yoghurt, and Punjabi Sikhs and Hindus ate dhal more frequently than Pakistani Moslems, Gujerati Moslems or Hindus. Most South Asians ate Indian sweets and ‘Western’ snacks.

The purpose of the present study was to investigate the interrelationship between carbohydrate and fat metabolism at rest after isoenergetic meals of varying proportions of carbohydrate and fat. Eight physically-active subjects (BMI 18·1–23·4 kg/m2) were studied at rest on three occasions after an overnight fast. In a balanced design they were given meals containing carbohydrate, protein and fat in the following amounts respectively (g/70 kg body weight): meal 1 121,16,48; meal 2 70,16,70; meal 3 50, 14, 80. All meals were isoenergetic, containing 4·0 MJ/70 kg body weight, and were of similar appearance. In addition, on a fourth occasion five of the eight subjects consumed meal 4 (g/70 kg body weight): Carbohydrate 0, protein 0, fat 108. Blood samples were taken before eating the meal and at intervals following the meal to determine metabolic and hormonal responses. Energy expenditure and substrate oxidation were measured by indirect calorimetry and balance was calculated over the 5 h postprandial period. The incremental areas under the time curves for fat oxidation were greatest after meals 3 and 4 (P<0·05), whereas incremental areas under thecarbohydrate oxidation v. time curves were relatively reduced after these two meals (P<0·05). This was accompanied by lesser suppression of plasma non-esterified fatty acid concentrations (P<0·001) and reduced plasma insulin concentrations (P<0·001) following these meals. Energy balance was almost identical after the three isoenergetic meals. In contrast, there was an inverse relationship between Carbohydrate and fat balance following these meals, with carbohydrate balance decreasing as carbohydrate intake decreased and fat balance increasing as fat intake increased. We conclude that there is a close interrelationship between carbohydrate and fat metabolism following isoenergetic meals in resting subjects.

The aim of the present study was to investigate in human subjects whether or not the ingestion of two liquid meals that differed only in their fatty acid composition (due to the addition of olive oil (group O) or sunflowerseed oil (group S) as the source of dietary fat) would lead to differences in the pancreatic enzyme activities secreted into the duodenum. The experiments were performed in eighteen cholecystectomized subjects who, during the 30d period immediately before surgery, modified their habitual diets in such a way that their fat composition would reflect, as far as possible, that of the experimental meals. Lipase (EC 3.1.1.3), colipase, amylase (EC 3.2.1.1), chymotrypsin (EC 3.4.21.1) and trypsin (EC 3.4.21.4) activities were measured in duodenal contents aspirated before and after the ingestion of the test meals. The plasma levels of secretin and cholecystokinin (CCK) were also examined. Duodenal enzyme activities were similar in resting conditions. No significant differences were revealed in postprandial enzyme activities, except for lipase activity, which was higher in group O, probably in relation to the greater plasma CCK concentrations observed in this group. In the absence of enzyme output data, we should not exclude the possibility that the type of dietary fat will affect human pancreatic enzyme secretion to a greater extent than is evident from the present study, for instance through a flow-mediated effect, as we previously observed in dogs.

Thirty-one men (47 (SD 14) years) and thirty-four women (35 (SD 13) years) took part in a 4-week randomized cross-over trial to compare the effect of six mugs of black tea daily v. placebo (water, caffeine, milk and sugar) on blood lipids, bowel habit and blood pressure, measured during a run-in period and at the end of weeks 2, 3 and 4 of the test periods. Compliance was established by adding a known amount of p–aminobenzoic acid (PABA) to selected tea bags, and then measuring its excretion in urine. Mean serum cholesterol values during run-in, placebo and on tea drinking were 5·67 (SD 1·05), 5·76 (SD 1·11) and 5·69 (SD 1·09)mmol/l (P=0·16). There were also no significant changes in diet, LDL-cholesterol, HDL-cholesterol, triacylglycerols, and blood pressure in the tea intervention period compared with placebo. Compared with placebo, stool consistency was softened with tea (P=0·04), and no other differences were found in bowel habit. Results were unchanged when fifteen ‘non-compliers’, whose PABA excretion indicated that fewer than six tea bags had been used, were excluded from the analysis, and when differences between run-in and tea periods were considered separately for those who were given tea first or second.

The clinical significance of low serum vitamin B12 levels in elderly people is controversial. We aimed to document the prevalence of a low serum vitamin B12 (<175pmol/l) in patients referred to a geriatric medical unit, and to determine whether haemopoiesis is commonly affected in elderly patients with low serum vitamin B12. We studied prospectively 472 consecutive referrals to a geriatric medical unit; fifty-six (13%) had a low serum vitamin B12 level, of whom nineteen (34%) of the fifty-six also had evidence of Fe deficiency (serum ferritin<45ng/ml). Low vitamin B12 was associated with a raised mean erythrocyte volume (MCV; mean 96·0 (SD 6·7) fl), compared with a control group (91·7 (SD 6·0) fl; P=0·001). However, only thirteen (23%) of the fifty-six patients with a low vitamin Blz had an MCV≥100 fl. Mean haemoglobin (Hb) levels were not significantly reduced in those with a low vitamin B12. In a subsequent study the haematological response to intramuscular hydroxocobalamin was examined in thirty-four patients with a low serum vitamin B12. Treatment resulted in a significant fall in MCV and rise in Hb; these effects could be detected both in those patients with an initially normal full blood count (change in MCV -1·2 (SD 1·2); Hb + 0·5 (SD 0·6); P<0·01) and in those with macrocytosis and/or anaemia (-9·1 (SD 11·8); + 0·8 (SD 1·2); P<0·05). A low serum vitamin B12 is common in geriatric medical patients. This is usually associated with an upset in erythropoiesis, although the abnormalities are often subtle and may not be apparent on inspection of the full blood count. Elderly patients with serum vitamin B12<175pmol/l should be assumed to have vitamin deficiency even if their full blood count is normal.

The influence of dietary Ca on peak bone mass and on subsequent bone loss is controversial. Despite this an assessment of nutritional status is often included in the clinical evaluation of osteoporosis risk. To assess the value of this we investigated the relationship between current diet and bone mineral density (BMD) in 426 postmenopausal women, aged 45–59 years, who were enrolled into an international multi-centre trial of alendronate for the prevention of postmenopausal osteoporosis. BMD of the lumbar spine and proximal femur was measured on two occasions approximately 2 weeks apart by dual-energy X-ray absorptiometry. Serum osteocalcin was measured by immunoradiometric assay and serum 25-hydroxycholecalciferol by radioimmunoassay. Dietary assessment was performed by analysis of a 3d unweighed dietary record, using Salford University's Microdiet software. BMD at both the lumbar spine and femoral neck correlated significantly with BMI, age, and average serum osteocalcin concentration. We therefore corrected for these variables in subsequent analyses. Dietary Ca intake ranged from 223 to 2197mg/d (median 852mg/d). Neither dietary Ca intake nor any other nutritional variable correlated significantly with BMD. There was a weak, but significant correlation between Ca intake and serum osteocalcin. We conclude that current diet does not correlate with BMD in early postmenopausal women. However, present diet may affect the rate of change of BMD, and this is supported by the finding of a significant relationship between dietary Ca and serum osteocalcin, a marker of bone formation rate.

The influence of Na load on bone metabolism was investigated in postmenopausal women using urinary deoxypyridinoline (DPD) as a marker of bone resorption. In a cross-over study, fourteen postmenopausal women were divided into two groups of seven. A fixed diet providing 816 mg Ca/d with either 60 or 170 mmol Na/d was consumed. At the end of an 8 d period the groups switched diets for a further 8d period. Urine was collected daily for the last 4d of each period. There was no significant difference in DPD excretion between high-Na and low-Na diets (129 nmol/d v. 132 nmol/d; P = 0·18). There was, however, a significant relationship (P = 0·02) between the changes in DPD excretion and urinary Ca. Plasma Mg fell from 0·83 to 0·81mmol/l on the high Na intake (P<0·001), but there was no significant effect on plasma Ca or intact parathyroid hormone levels. It is concluded that varying dietary Na intake may affect Ca and Mg metabolism, but we were unable to demonstrate an effect on bone resorption at the levels of intake used

Ten adult female mink (Mustela vison) were studied in a 7 d balance experiment consisting of a 2 d pre-surgery feeding period, followed by surgery, 1 d of recovery, 4 d of ad libitum feeding, and a 2d fasting period. In this experiment (Expt A) the animals had osmoticpumps implanted for continuous release of radioactively-labelled p–aminohippuric acid (p–aminobenzoyl-2-[3H]glycine; [3H]PAH;n10) and 14C-labelled inulin ([14C]IN; n 5). Repeated 24 h collections of urine, corrected to 100%[3H]PAH or [14C]IN recovery, were used for accurate determination of N balances, 24 h urinary excretion of urea, creatinine, and total N, and calculation of mean 24 h renal clearance rates for endogenous creatinine and inulin. N balances were slightly below zero, but not significantly different between feeding and fasting periods, indicating that correction to 100% [3H]PAH recovery resulted in slight overestimation of thefinal balances. During fasting, withdrawal of the dietary water and protein loads resulted in a dramatic decline in 24 h urinary volume, and urea and creatinine excretion. Large individualvariations in 24h urinary creatinine excretion (with relative variation coefficients up to 30%) confirmed that this is an unreliable index of the completeness of urine collection. In this respect, recovery rates of [3H]PAH proved far more consistent. Renal clearance values obtained in fed mink were in fair agreement with published data from cats, dogs and ferrets (Mustela putorius furo). Inulin clearance was about 30% higher than endogenous creatinine clearance, although its decline in response to fasting was not significant. In a separate study (Expt B)another ten female mink were equipped with osmotic pumps containing [3H]PAH for determination of 24 h excretion rates of purine derivatives. During feeding, allantoin accounted for more than 97 % of the excretion of purine derivatives in urine, uric acid making up less than 2·5%, xanthine and hypoxanthine less than 1 %. In fasted animals, urinary excretion of each of these purine derivatives declined to less than 50% of the feeding value. In conclusion, an experimental technique is presented for efficient and accurate measurements of daily urinary excretion of nitrogenous constituents, which allows for correct determination of N balances in adult mink and, presumably, in other mammalian species.

The aim of the study was to evaluate the functional role of reticular contractions for digesta passage in sheep. Feed intake, mean retention time of fluid and plastic particles in the reticulo-rumen, rumen fluid volume, forestomach motility and particle size distribution in the faeces were determined in five rumen-fistulated sheep fed on hay ad libitum (Expt 1). The same variables were determined when reticular movements were impaired for 10 d by introducing a silicone-covered lead weight (500 g) into the reticulum (Expt 2). As feed intake dropped in Expt 2 by 27% compared with Expt 1, the sheep received in an additional experiment exactly the amount of feed which had been consumed during Expt 2 and measurements were repeated without impairing reticular movements (Expt 3). The introduction of the weight did not affect the frequency of A- or B-cycles, but elevation of the reticular floor in a cranio-dorsal direction during the biphasic contraction was markedly reduced. The pattern of marker excretion indicated a drastically changed composition of reticular outflow in Expt 2 compared with Expts 1 and 3. During Expt 2, rumen fluid volume was similar to that in Expt 1 but about 25% higher than that in Expt 3; the amount of large feed particles in the faeces was increased compared with Expt 1 ( + 49%) and Expt 3 ( + 76%). In at least two sheep, abomasal emptying was inhibited during Expt 2, as indicated by an enlarged impacted abomasum. In conclusion, the results emphasize the central role of reticular motility for the separation of particles in the forestomach, the outflow of digesta from the reticulo-rumen and transpyloric digesta flow.

Broiler chicks were fed on chemically-defined crystalline amino acid diets containing graded levels of L-threonine (Thr) during the period 10–20 d post-hatching. Doses of Thr represented 5,10,15,40,55,70 and 95% of its ideal level for maximal weight gain and feed efficiency. Other amino acids were maintained at minimized excess levels that were 15% (of ideal) above the various doses of Thr. Following 10d of feeding and a 24h fast, chicks were killed for whole-body protein and amino acid analysis. Using pen accretion means, weight gain (r20·98), protein accretion (r2 0·99), and Thr accretion (r2 0·99) were linear (P<0·01) functions of Thr intake. Slope of the Thr accretion regression line indicated that 82% of the Thr intake was recovered in whole-body protein. At zero Thr intake, chicks lost 11·9 mg Thr/d. The Thr maintenance requirement was 45·7 mg/d per kg body weight 0·75. Increasing doses of Thr resulted in increased (P<0·05) concentrations of methionine, isoleucine, histidine and lysine in whole-body protein. Other indispensable amino acids, including Thr, also tended to increase. Whole-body glycine, proline, serine and cystine concentrations decreased (P<0·05) as Thr was increased in the diet. The maintenance need for Thr represented 5·5% of the total need for Thr. The data suggest that efficiency of Thr utilization is constant at all levels of Thr intake between 5 and 95% of the level required for maximal weight gain and feed efficiency.

It is becoming well established that poor fetal and early postnatal growth can have long-term effects on adult health, including susceptibility to non-insulin-dependent diabetes mellitus, cardiovascular disease and hypertension. It is suggested that this results from poor nutrition during early life having permanent effects on the structure and metabolism of certain organs and tissues. In the present study we investigated the effect of a low-protein diet during pregnancy and lactation on adipocyte properties and glucose tolerance. Rat dams were fed on a diet containing either 200 (control) or 80 (low protein) g protein/kg during pregnancy and lactation. In addition cross-fostering techniques were employed to enable a separate evaluation of the prenatal and postnatal periods. All offspring were weaned onto a 200 g protein/kg diet at 21 d of age and then studied at 6 weeks of age. The mothers' protein supply during lactation appeared to be the most critical time window for longterm growth. In contrast, the offspring of mothers fed on a low-protein diet during pregnancy or lactation were significantly more glucose tolerant than controls, suggesting that both time windows can have long-term effects on glucose tolerance. In addition off spring of mothers fed on a lowprotein diet during pregnancy or lactation had significantly smaller adipocytes than controls. However the largest reduction in adipocyte size was observed when there was a low-protein diet during both pregnancy and lactation. The amount of insulin receptor present in adipocyte membranes was increased in the three animal groups that had been exposed to the low-protein diets while levels of the insulin responsive glucose transporter (GLUT 4) were similar in adipocyte membranes from all groups.