This paper assesses critically the science base that underpins the argument that oxidative damage is a significant causative factor in the development of human diseases and that antioxidants are capable of preventing or ameliorating these disease processes. The assessment has been carried out under a number of headings, and some recommendations for future research are made based on the present day knowledge base.

Lutein, one of the major carotenoids present in serum, is also widely consumed by most populations. For the purpose of testing the potential health benefits of several carotenoids, lutein was supplied as part of an intervention trial to test whether the consumption of these food constituents reduces oxidative damage to human tissue components. Lutein from a natural source (15 mg/d as mixed ester forms) was supplied for 4 months to eighteen non-smoking, apparently healthy volunteers (nine men, nine women) aged 25–45 years. The serum carotenoid profile was analysed at baseline and monthly thereafter. On average, lutein concentrations increased 5-fold after the first month of supplementation (mean 1·34 (range 0·6–3·34) μmol/l). On reviewing the results, in those volunteers whose lutein levels surpassed 1·05 μmol/l (fourteeen of seventeen), we tentatively identified lutein monopalmitate along with another unidentified ester (possibly from a monoketocarotenoid) in serum. Lutein levels returned to baseline values and ester forms were not present 3 months after supplementation was discontinued. Their concentrations did not correlate with, and represented less than 3% of, lutein levels achieved in serum. They were observed before development of, and despite the presence of, carotenodermia. To our knowledge, this is the first time xanthophyll esters have been described in human serum. In view of the fact that xanthophyll esters have not been previously reported in serum and chylomicrons, it seems unlikely that these ester forms would be a reflection of the contents of the capsule. They may indicate a ‘ceiling effect’ on or saturation of the transport capacity for xanthophylls, and may have been re-esterified in vivo because of the unusual dietary conditions. The determination of the physiological importance of this finding will require further investigation, although neither haematological nor biochemical changes were detected.

I intake and I deficiency were investigated in thirty vegans (eleven males and nineteen females) consuming their habitual diet. I intake was estimated using the chemical analysis of 4 d weighed duplicate diet collections. The probability of I-deficiency disorders (IDD) was judged from the measurement of urinary I excretion in 24 h urine specimens during the 4 d. There was wide variation in I intake. Mean I intake in males was lower than the reference nutrient intake (RNI; Department of Health, 1991) and mean intake in females was above the RNI, although 36% males and 63% females had I intakes below the lower RNI. Mean I intake in subjects who consumed seaweed (n 3) was in excess of the RNI, and approached the provisional maximum tolerable daily intake (World Health Organization/Food and Agriculture Organization Joint Expert Committee on Food Additives, 1989). The probability of IDD in the group investigated was moderate to severe: three of five subgroups were classified as moderate and two subgroups were classified as severe IDD possibility. The findings highlight that vegans are an ‘at risk’ group for I deficiency. The I status of vegans and the subclinical effects of low I intakes and infrequent high I intakes on thyroid function in this group should be further studied. Our work has also raised the question of adequate I intakes in groups where cow's milk is not consumed, and has exposed a need for more research in this area.

To study the relationship between lycopene intake and plasma concentration, ten healthy female subjects were given one or more portions of tomato purée or fresh raw tomato containing 16.5mg total lycopene (all-trans + cis forms). In Expt 1 subjects (n 9) were randomly assigned the single portions of the two tomato products and blood samples were collected to follow the change in plasma carotenoid concentrations within the first 12 h and on each of the following 5 d (104 h). In Expt 2 subjects (n 10) were divided into two groups of five each receiving daily dietary portions of tomato purée or fresh raw tomato containing 16.5mg total lycopene for 7 d. Fasting blood samples were collected daily. In Expt 1 the plasma total lycopene (all-trans + cis forms) concentration, after the single portions of tomato purée and raw tomato, varied significantly over time, with a first peak reached after 6 h, a further increase after 12 h and a slow decrease until 104 h. In Expt 2, when the tomato products were given daily, there was a day-by-day increase in the plasma total lycopene concentration, and through the following week of a diet without tomato there was a gradual decrease. However, values did not return to basal concentrations. Plasma total lycopene concentration was higher after the tomato purée intake than after the raw tomato in both the first (F (1,8) 7.597; P < 0.025) and the second experiments (F (1,8) 12.193; P < 0.01) demonstrating a significant effect of food matrix on absorption.

Oligofructose and inulin, selective fermentable chicory fructans, have been shown to stimulate the growth of bifidobacteria which are regarded as beneficial strains in the colon. Studies were designed to evaluate inulin (Raftiline) and oligofructose (Raftilose), for their potential inhibitory properties against aberrant crypt foci (ACF) formation in the colon of rats. ACF are putative preneoplastic lesions from which adenomas and carcinomas may develop. The results of this study demonstrate that dietary administration of oligofructose and inulin inhibits the formation of preneoplastic lesions in the colon suggesting the potential colon tumour inhibitory properties of chicory fructans. Since these prebiotics selectively stimulate the growth of bifidobacteria, tumour inhibitory activity of lyophilized cultures of Bifidobacterium longum (BL) against azoxymethane (AOM)-induced colon carcinogenesis in rats and modulating effect of these cultures on colonic tumour cell proliferation, ornithine decarboxylase (ODC) activity, and ras-p21 oncoprotein expression were investigated. Dietary administration of lyophilized cultures of BL strongly suppressed AOM-induced colon tumour development. Inhibition of colon carcinogenesis was associated with a decrease in colonic mucosal cell proliferation and colonic mucosal and tumour ODC and ras-p21 activities.

Thirty-six normal-weight, habitual snackers (eighteen males, eighteen females) completed a medium-term intervention study designed to examine the tendency of four different types of snacks, varying in nutrient (low- (LF) or high-fat (HF)) and sensory properties (sweet (SW) or non-sweet (NSW)), to influence the control of appetite and to adjust daily energy intake. Subjects were exposed to each snack category for a 3-week period and were asked to consume a minimum number of snacks each day so that at least 25% of their daily energy intake would be derived from the test snacks. Energy and macronutrient intakes from the test snacks were calculated every day and also from other eating episodes (using 3 d food diary records) during the third week of snack exposure. Subjects consumed more energy/d from the SW snacks than from the NSW snacks, with most energy being consumed from the HF/SW snacks (3213 kJ) and least energy from the LF/NSW snacks (1628 kJ). This differential snack intake remained stable across the whole snack exposure period. Total daily energy intake did not differ significantly during exposure to any of the four snack types. Furthermore, the encouragement to eat freely from the test snacks did not lead to daily overconsumption of energy when compared with pre-study intakes. Hence, the level of snack consumption was largely compensated for by the energy consumed from the rest of the eating pattern. Although daily energy intake during exposure to the HF snacks was an average of 364 kJ higher (NS) than that during exposure to the LF snacks, the clearest and most significant effect of snack consumption was on daily macronutrient intake. Appreciable consumption of the HF snacks raised the percentage of total daily energy intake consumed as fat from 37 to 41% (P < 0.01). In contrast, the LF snacks reduced daily fat intake to 33.5% (LF/SW, P < 0.05; LF/NSW, NS) of total daily energy. The results, therefore, suggest that, in habitual snackers, generous consumption of LF snacks, when compared with HF snacks, is an effective strategy to reduce fat intake so that it approaches the recommendations of dietary guidelines without increasing total daily energy intake.

We have compared the effects on lipoproteins and haemostatic variables of two hard margarines with similar functional properties, one traditional margarine containing partially hydrogenated fish oil (PHFO), and one experimental margarine based on vegetable oil (VO). Both were all-purpose cooking margarines with nearly identical functional properties. Trans fatty acids from PHFO in the traditional margarine were replaced mostly by saturated, monounsaturated and trans fatty acids of vegetable origin in the new formulation. Both test margarines contained approximately the same amount of cis polyunsaturated fatty acids. Sixteen female normolipidaemic students consumed each diet with the two test margarines for 14 d in random order (crossover design). The amount of fat was 31 % energy in the PHFO diet and 32 % energy in the VO diet. The test margarines provided approximately 26% energy in both diets. In the PHFO diet 7.8 % of the energy was derived from trans fatty acids and 9.2 % from saturated fatty acids (12:0, 14:0 and 16:0) while in the VO diet, 1.1 % energy was derived from trans fatty acids and 13.3% from saturated fatty acids (12:0, 14:0 and 16:0). The natural content of cholesterol in PHFO was deliberately not balanced by addition of cholesterol to the VO diet, thus the PHFO diet contained 215 mg and the VO diet 86 mg cholesterol per 8.5 MJ. LDL-cholesterol concentration was 19 % higher in subjects on the PHFO diet compared with the VO diet (P < 0.01). The ratio LDL-cholesterol:HDL-cholesterol was 12.6 % higher in subjects on the PHFO diet compared with the VO diet (P < 0.01). The level of apolipoprotein (apo)A-I was 6 % lower in subjects on the PHFO diet compared with the VO diet (P < 0.01). The ratio apoB:apoA-I was 10.4 % higher in subjects on the PHFO diet than on the VO diet (P < 0.01). There were no significant differences in total cholesterol, HDL-cholesterol, triacylglycerols, apoB, lipoprotein(a) and haemostatic variables between the diets. Our results demonstrate that PHFO, with its unfavourable effects on plasma lipids, can be replaced by vegetable oils in margarine without appreciable loss of functional properties but with significant improvement in the effects on plasma lipoproteins.

The effects of gestational age at delivery (GA), postnatal age (PNA) and post-menstrual age (PMA=PNA+GA, an indicator of autonomous developmental processes not affected by the moment of birth) on macronutrient composition of very preterm milk were studied. Total N, fat, lactose and carbohydrate concentrations, energy density and 24 h volume were determined in 282 24 h milk samples collected at weekly intervals (days 7–55 of lactation) from seventy-nine women delivering their babies between 25 and 29 weeks of gestation. GA related differences were found for carbohydrate concentration only: carbohydrate concentration was lower with increasing GA. PNA was related to a decrease in total N and an increase in lactose concentration. PMA was not related to milk composition. Our data indicate that PNA strongly influences the development of the composition of very preterm human milk, while GA affects carbohydrate content with a negligible effect on the nutritional value of the milk. We conclude that in accordance with current opinion in paediatrics, human milk is the best source of nutrients even for very preterm (< 30 weeks GA) infants.

Two N balance experiments using growing pigs were conducted to study the effect of essential:total (E:T) N ratio on N retention and utilization. Purified diets contained casein and crystalline amino acids as the sole sources of N. E:T values ranged from 0·25 to 0·86 while either the concentration of total N (Expt. 1) or essential N (Expt 2) was kept constant. At a constant concentration of total dietary N, N retention and total N utilization were maximized with an E:T value of approximately 0·6, while essential N utilization gradually decreased as E:T increased. At a constant level of essential N, N retention remained unchanged until the E:T value reached 0·48 and then decreased. In Expt 2, maximum total N utilization was attained with an E:T value of 0·66 while N excretion and essential N utilization decreased with increased E:T value. These results suggest that under conditions of optimal protein utilization, essential amino acids are partially degraded and used for the synthesis of non-essential amino acids.

Sucrose polyester (SPE) is a tasteless, odourless substance which reduces plasma cholesterol concentrations and may therefore be valuable as a fat substitute in human foodstuffs. It has recently been approved for use in snack foods by the United States Federal Drug Administration. The current study was designed to investigate its effects on gastrointestinal physiology and nutrient absorption in human subjects. A 6-month (2×3-month periods) double-blind, lacebo-controlled, randomized, cross-over trial of SPE and control fat was performed in healthy free-living volunteers. Subjects consumed 20–40 g of SPE daily (mean 26·8 (se 6·8) g) which reduced the intake of total and saturated fat but had no effect on energy intake or body weight. Plasma cholesterol and triacylglycerols were reduced. The frequency of bowel movements and their urgency were increased and anal leakage occured in 7·2% of subjects. Abdominal pain was more frequent in subjects receiving SPE and was significantly greater than in the control group after 8 weeks feeding. The plasma concentrations of vitamin E and six carotenoids were significantly reduced. Routine haematology and biochemistry, other vitamins, intestinal biopsies, bile-salt retention, rectal prostaglandins, fractional Ca absorption and aminopyrine metabolism were unaffected. The ingestion of foods containing 20–40 g SPE daily provoked significant gastro-intestinal problems. This intake is greater than that to be expected from the use of SPE in savoury snack foods, for which it has been approved by the United States Federal Drug Administration. However, the favourable effects on lipid profiles must be balanced against the reduction in the concentrations of vitamins and carotenoids, as these compounds may have beneficial effects on health through protection from free-radical oxidative stress.

Cardiovascular disease has a multifactorial aetiology, as is illustrated by the existence of numerous risk indicators, many of which can be influenced by dietary means. It should be recalled, however, that only after a cause-and-effect relationship has been established between the disease and a given risk indicator (called a risk factor in that case), can modifying this factor be expected to affect disease morbidity and mortality. In this paper, effects of diet on cardiovascular risk are reviewed, with special emphasis on modification of the plasma lipoprotein profile and of hypertension. In addition, dietary influences on arterial thrombotic processes, immunological interactions, insulin resistance and hyperhomocysteinaemia are discussed. Diet-ary lipids are able to affect lipoprotein metabolism in a significant way, thereby modifying the risk of cardiovascular disease. However, more research is required concerning the possible interactions between the various dietary fatty acids, and between fatty acids and dietary cholesterol. In addition, more studies are needed with respect to the possible importance of the postprandial state. Although in the aetiology of hypertension the genetic component is definitely stronger than environmental factors, some benefit in terms of the development and coronary complications of atherosclerosis in hypertensive patients can be expected from fatty acids such as α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid. This particularly holds for those subjects where the hypertensive mechanism involves the formation of thromboxane A2 and/or α1-adrenergic activities. However, large-scale trials are required to test this contention. Certain aspects of blood platelet function, blood coagulability, and fibrinolytic activity are associated with cardiovascular risk, but causality has been insufficiently proven. Nonetheless, well-designed intervention studies should be initiated to further evaluate such promising dietary components as the various n−3 and n−6 fatty acids and their combination, antioxidants, fibre, etc. for their effect on processes participating in arterial thrombus formation. Long-chain polyenes of the n−3 family and antioxidants can modify the activity of immunocompetent cells, but we are at an early stage of examining the role of immune function on the development of atherosclerotic plaques. Actually, there is little, if any, evidence that dietary modulation of immune system responses of cells participating in atherogenesis exerts beneficial effects. Although it seems feasible to modulate insulin sensitivity and subsequent cardiovascular risk factors by decreasing the total amount of dietary fat and increasing the proportion of polyunsaturated fatty acids, additional studies on the efficacy of specific fatty acids, dietary fibre, and low-energy diets, as well as on the mechanisms involved are required to understand the real function of these dietary components. Finally, dietary supplements containing folate and vitamins B6 and/or B12 should be tested for their potential to reduce cardiovascular risk by lowering the plasma level of homocysteine.

The effect of partial dietary replacement of linoleic acid (18:2n-6; linoleic acid-rich diet) with α-linolenic acid (18:3n-3; α-linolenic acid-rich diet) on plasma lipids was investigated in twenty-nine healthy young men. After a 2-week stabilization period subjects were randomly assigned to either the α-linolenic acid-rich diet group (n 15), receiving a mean of 10.1 g of α-linolenic acid and 12.1 g of linoleic acid/d, or the linoleic acid-rich diet group (n 14), receiving a mean of 1.0 g of α-linolenic acid and 21.0 g of linoleic acid/d, for a 6-week test period. Blood samples were taken at the commencement of the stabilization period and at the start (week 0), midpoint (week 3) and endpoint (week 6) of the test period and plasma lipids analysed. The changes occurring on the linoleic acid-rich diet and α-linolenic acid-rich diet were compared but no significant differences in the changes in plasma total cholesterol, LDL-cholesterol, HDL-cholesterol, the subfractions HDL2 and HDL3 or triacylglycerols were found. These results indicate that dietary replacement of linoleic acid with α-linolenic acid in the diet of healthy male subjects offers similar cardioprotective benefits with respect to lipid metabolism.

In a longitudinal study of child growth and nutritional status in Bangladesh, child morbidity was recorded using health interviews with the mother. The aim of the present study was to establish whether maternal reports of child illness were associated with the biochemical health status of the child. Children aged 2–5 years (n 117) took part in the study and their mothers were interviewed every fortnight by Bangladeshi fieldworkers. Maternal reports of diarrhoea were associated with significantly lower plasma albumin concentrations (P < 0·001), poorer intestinal permeability (P < 0·001), higher plasma immunoglobulin A levels (P < 0·005) and higher α-1-antichymotrypsin (ACT) levels (P < 0·05) compared with children reported to be healthy. Children with fever had significantly higher ACT (P < 0·001) and lower albumin (P < 0·05) levels compared with their healthy counterparts. Respiratory infections (RI) were not associated with any significant changes; however, reports of RI with fever were associated with significantly higher levels of ACT than either illness individually (interaction P < 0·05). These highly significant associations between maternal reports of illness and biochemical profiles of child health support the use of health interviews in developing countries.

Since the early work of Mann and Spoerry, probiotics in the form of fermented milk products have been reputed to have cholesterol-lowering properties in humans. However, studies conducted since the early 1970s have produced equivocal findings, with interpretation of the outcomes complicated by use of excessive quantities of product, inadequate sample sizes, failure to control nutrient intake and energy expenditure and variations in baseline blood lipids. More recent studies are of better quality, but fail to provide convincing evidence that ‘live’ fermented milk products have cholesterol-lowering efficacy in man. Future studies using probiotics should ensure adequate sample sizes sufficient to detect relatively small changes in blood cholesterol and should be conducted over longer periods of time. The recent introduction of the concept of prebiotics has directed attention towards the possibility that alterations in gut microflora induced by the fermentation of non-digestible components of the diet may also have the potential to influence systemic lipid metabolism. This possibility has been strengthened by the observation that in animals, dietary oligofructosaccharides cause suppression of hepatic triglyceride and VLDL synthesis, resulting in marked reductions in triglyceride, and to a lesser extent cholesterol, levels. Evidence for similar effects in humans is sparse and more studies are needed, particularly with respect to effects on postprandial triglyceride concentrations.

The present study investigated whether the extent of fermentation of NSP in human subjects could be predicted by an in vitro batch system. Fibre sources studied were five mixed diets containing different amounts and types of fibre and three single fibre sources (citrus fibre concentrate, coarse and fine wholemeal rye bread). Fermentation in human subjects was determined in balance experiments in women who were also donors of the faecal inocula. In vitro fermentations were performed with fibre residues prepared from duplicates of the fibre-containing foods consumed during the balance trials. Fermentation of total NSP in vivo was between 65.8 and 88.6% for the mixed diets and 54.4, 58.0 and 96.9 % for the coarse and fine wholemeal rye breads and the citrus fibre concentrate respectively. For the mixed diets and the citrus fibre concentrate, mean differences between the extent of NSP degradation after 24 h in vitro incubation and that in vivo were between −0.7 and 5.0 %. Differences were significant for one diet (P < 0.05). For the wholemeal rye breads, the fermentation in vitro exceeded that in vivo significantly, but the magnitude of the difference in each case was small and without physiological importance. Particle size of breads had no influence on the extent of NSP degradation. These results indicate that the in vitro batch system used could provide quantitative data on the fermentation in vivo of NSP in mixed diets and some single fibre sources. An in vitro incubation time of 24 h was sufficient to mimic the NSP degradation in vivo.

The physiological importance and mechanism of the postprandial fall in plasma Zn concentration is not well understood. In order to gain further information on this apparent redistribution of plasma Zn, a stable isotope, 70Zn, was used to study the effect of a breakfast meal on plasma Zn kinetics. Nine women participated in two trials, a fasting trial and a breakfast-meal trial; five of the women participated in a third trial in which the energy content of the breakfast meal was doubled. At each trial, 0.1mg of 70Zn was infused intravenously, and the plasma disappearance of the isotope was analysed using a two-compartment model of Zn kinetics. Plasma Zn concentration fell significantly following the two trials in which the subjects were given meals, reaching low points that were 13 and 19 %, respectively, below concentrations at comparable times during the fasting trial. Kinetic analysis revealed that after the doubled breakfast meal there was a significant fall (P < 0.007) in the size of the most rapidly turning over Zn pool (pool (a)) from 2.90 (se 0.13)mg in the fasting state to 2.47 (se 0.14) mg postprandially. The fractional turnover rate of pool (a) to other extravascular Zn pools, i.e. outside the two-compartment system, was also significantly elevated after the doubled breakfast meal (P < 0.05). These results suggest that the decline in plasma Zn concentration following a meal is due to a redistribution of Zn from the plasma to other more slowly turning over extravascular pools that may be involved in the assimilation and metabolism of fuels following food intake.

The gut is an obvious target for the development of functional foods, acting as it does as the interface between diet and the metabolic events which sustain life. The key processes in digestive physiology which can be regulated by modifying diet are satiety, the rate and extent of macronutrient breakdown and absorption from the small bowel, sterol metabolism, the colonic microflora, fermentation, mucosal function and bowel habit, and the gut immune system. The intestinal microflora is the main focus of many current functional foods. Probiotics are foods which contain live bacteria which are beneficial to health whilst prebiotics, such as certain non-digestible oligosaccharides which selectively stimulate the growth of bifidobacteria in the colon, are already on the market. Their claimed benefits are to alleviate lactose maldigestion, increase resistance to invasion by pathogenic species of bacteria in the gut, stimulate the immune system and possibly protect against cancer. There are very few reports of well-designed human intervention studies with prebiotics as yet. Certain probiotic species have been shown to shorten the duration of rotavirus diarrhoea in children but much more work is needed on the mechanism of immunomodulation and of competitive exclusion and microflora modification. The develop-ment of functional foods for the gut is in its infancy and will be successful only if more fundamental research is done on digestive physiology, the gut microflora, immune system and mucosal function.

The demand for glycine to satisfy normal growth during early life is considerable and most has to be made endogenously. The extent to which adequate glycine is available can be assessed by measuring the urinary excretion of 5-L-oxoproline. The excretion of 5-L-oxoproline at 6 weeks of age for infants in Trinidad of African, Indian or mixed parentage (398 μmol/mmol creatinine) was significantly greater than for infants born in England of Caucasian parentage (194 μmol/mmol creatinine). There was no relationship between 5-L-oxoproline excretion and either sex or pattern of feeding. There were significant inverse relationships between 5-L-oxoproline/creatinine and birth weight, and head circumference either at birth or 6 weeks of age, suggesting that limited availability of glycine is associated with poorer growth before and after birth. For a group of infants born in England of Indian parentage, excretion of 5-L-oxoproline (155 μmol/mmol creatinine) was not different to infants of Caucasian parentage, but significantly less than infants born in Trinidad. The demonstration that 5-L-oxoproline/creatinine was similar in infants born in England, regardless of parentage, shows that the differences between England and Trinidad are related to environment and are unlikely to be accounted for by genetic differences or ethnicity.

The effect of acute (4.5 h) infusions into the mesenteric vein of an amino acid (AA) mixture, which simulated the composition of rumen microbial protein, on net transfers of NH3, urea and total AA across the portal-drained viscera (PDV) and liver in the ovine has been examined. Four wether sheep were surgically prepared with vascular catheters across the PDV and liver (Lobley et al. 1995) and were offered a basal diet of 1000 g grass pellets/d (approximately 1.4 × energy maintenance). Each animal was infused at weekly intervals with one of four dilutions of the AA mixture. These dilutions provided 0.44, 0.88, 1.32 and 1.84mmol AA-N/min infused, the lowest of which approximately doubled the net absorption of AA-N from the basal diet. Animals were treated with heparin to allow continuous collection of blood by peristaltic pump for 2 h preceding, and between 0.5–2.5 and 2.5–4.5 h after, the start of the AA infusions. Blood flow in the hepatic artery increased (100 v. 208 g/min; P = 0.002) in response to AA infusion, while hepatic portal venous flow decreased (2090 v. 1854 g/min; P = 0.006). The AA infusion also stimulated O2 uptake by the PDV (P < 0.001) and liver (P = 0.016). Absorption across the PDV and hepatic removal of NH3 were unchanged between basal and amino acid infusion conditions. Urea-N removal across the PDV was unaltered, but hepatic production increased (P < 0.001) with level of AA infusion. During infusions, net appearance of AA across the PDV was below the theoretical level. This may have been due to inhibition of AA uptake from the small intestine, and/or increased removal by the digestive tract of AA from the systemic circulation associated with greater arterial concentrations. Hepatic extraction of AA increased with level of infusion, both for total AA and those included in the infusate. Total hepatic urea-N production tended towards a maximum (estimated as 2 μmol N/g liver wet weight per min). The AA removed by the liver and not used for ureagenesis remained similar (170 μmol AA-N/min) between basal and AA infusions. This was presumed available for anabolic purposes (mainly synthesis of export proteins). The proportion of net AA-N appearance (absorption plus infused) across the PDV removed by the liver declined from 0.71 to 0.53 between basal and AA infusions. In contrast to findings from cattle (Wray-Cahen et al. 1997), increased AA infusion did not alter the net removal of glutamine across the liver. This may reflect differences between the studies in NH3: AA-N absorbed. Further differences between the cattle study and the current findings may relate to the different physiological state (pregnancy v. growth), which may alter the partition of AA between anabolic and catabolic fates.

A growing number of food manufacturers in western Europe are beginning to explore the commercial opportunities for foodstuffs containing health-promoting microbial food supplements (probiotics) and health-promoting non-digestible food ingredients (prebiotics). A prebiotic is considered to affect the host beneficially by selectively stimulating the growth and/or activity of one or a limited number of naturally present or introduced bacterial species in the colon, also leading to a claimed improvement in host health. Increasingly, probiotics and prebiotics are used in combination, this being termed a synbiotic (Gibson & Roberfroid, 1995). Throughout European history, fermented milk products in particular have been considered beneficial to health, but only in recent years has there been scientific support for these beliefs. Issues considered important to the continuing development of this growing market are proof of safety, proof of efficacy, consumer education, market positioning, price and appropriate health claims strategies. Until recently, much of the innovation in the use of probiotics and prebiotics has been in the dairy cabinet, with an ever-growing number and range of ‘health-promoting’ yoghurts and yoghurt-type fermented milk being made available to the European consumer, a market which is currently estimated to be worth in excess of $US2 billion per annum (Hilliam et al. 1997). However, prebiotics are beginning to find increasing application outside the dairy sector, particularly in baked goods. A key driver behind the broadening application of prebiotics has been the pro-active stance taken by key prebiotic suppliers such as Beghin-Say, Orafti and Cosucra. To date, market activity in probiotic- and prebiotic-containing foods has centred around three health propositions, namely improving general gut health, lowering blood cholesterol and improving the body's natural defences.