Previous work in our laboratory demonstrated that a virus could undergo rapid mutation in a host deficient in Se, leading to a normally avirulent virus acquiring virulence due to genome changes. Once these mutations occur, even a host with adequate Se-nutriture is susceptible to the newly virulent virus. What influence does the deficiency in Se have on the immune response of the host? Infection with myocarditic strains of coxsackievirus induces an inflammatory response in the cardiac tissue. It is this immune response that induces the heart damage, rather than direct viral effects on the heart tissue. Chemokines are chemo-attractant molecules that are secreted during an infection in order to attract immune cells to the site of the injury, and have been found to be important for the development of coxsackievirus-induced myocarditis. We found that a deficiency in Se influences the expression of mRNA for the chemokine monocyte chemo-attractant protein-1, which may have implications for the development of myocarditis in the Se-deficient host. Expression of mRNA for interferon-γ was also greatly decreased in the Se-deficient animal. Thus, a deficiency in Se can have profound effects on the host as well as on the virus itself. How the alteration of the immune response of the Se-deficient animal affects the development of the virulent genotype remains to be answered.

The period of growth and development between birth and weaning is crucial for the long-term well-being of the organism. Protein deposition is very rapid, is achieved with a high nutritional efficiency, and is accompanied by marked differences in the growth rates of individual tissues and a series of maturational processes. These important aspects of development occur while the neonate is consuming a single and highly-specific food source, milk. Surprisingly, although there is a clear relationship between the nutrient density of milk and the growth rate of its recipient, this relationship does not apply to the overall amino acid composition of mixed milk proteins. Some amino acids, notably glycine and arginine, are supplied in milk in quantities that are much less than the needs of the neonate. The milk-fed neonate is therefore capable of carrying out a tightly-regulated transfer of N from amino acids in excess to those that are deficient. The rapid growth of the neonate is supported by a high rate of tissue protein synthesis. This process appears to be activated by the consumption of the first meals of colostrum. Recent research has identified that skeletal muscle and the brain are specifically responsive to an unidentified factor in colostrum. Following the initial anabolic response the rate of protein synthesis in some tissues, notably muscle, falls from birth to weaning. This decrease reflects a progressively smaller anabolic response to nutrient intake, which not only involves an overall fall in the capacity for protein synthesis, but also in responses to insulin and amino acids. The study of growth and protein metabolism, and their regulation in the neonate is not only important for pediatrics, but may provide important pointers to more general aspects of regulation that could be applied to the nutrition of the mature animal.

It has been proposed that there are critical periods during childhood that influence the development of obesity, including gestation and early infancy, the period of adiposity rebound that occurs between ages 5 and 7 years, and adolescence. Despite an extensive literature, there is to date only modest evidence for most of the factors such as nutrition, physical activity and other behavioural factors that are suspected as playing a role in the development of obesity. A recent review of this evidence (Parsons et al. 1999) showed, however, a consistent relationship between socio-economic status (SES) of origin and adult obesity, whereby those from lower SES backgrounds were fatter subsequently in adulthood. This association appeared to apply to both men and women, a finding that contrasts with the trends observed in cross-sectional studies, of an association with SES for women only. There are several potential explanations for the SES of origin–adult obesity relationship. SES of origin may be confounded by parental body size; studies to date provide insufficient evidence of an independent association with SES after allowing for parental body size. Alternatively, environment in early life (for which SES of origin is a proxy measure) may have a long-term impact on obesity later in adulthood, through one or more of several processes. Three major potential explanations can be identified: (1) nutrition in infancy and childhood, either over- or undernutrition, followed subsequently by overnutrition; (2) psychological factors, possibly involving emotional deprivation in childhood; (3) cultural or social norms regarding dietary restraint and attitudes to fatness that may be acquired during childhood.

The substrate demands of lactation must be met by increased dietary intake or by mobilization of nutrients from tissues. The capacity of animals to rely on stored nutrients depends to a large extent on body size; large animals have greater stores, relative to the demands of lactation, than do small animals. The substrate demands of lactation depend on the composition and amount of milk produced. Animals that fast or feed little during lactation are expected to produce milks low in sugar but high in fat, in order to minimize needs for gluconeogenesis while sustaining energy transfers to the young. The patterns of nutrient transfer are reviewed for four taxonomic groups that fast during part of or throughout lactation: sea lions and fur seals (Carnivora: Otariidae), bears (Carnivora: Ursidae), true seals (Carnivora: Phocidae) and baleen whales (Cetacea: Mysticeti). All these groups produce low-sugar high-fat milks, although the length of lactation, rate of milk production and growth of the young are variable. Milk protein concentrations also tend to be low, if considered in relation to milk energy content. Maternal reserves are heavily exploited for milk production in these taxa. The amounts of lipid transferred to the young represent about one-fifth to one-third of maternal lipid stores; the relative amount of the gross energy of the body transferred in the milk is similar. Some seals and bears also transfer up to 16–18 % of the maternal body protein via milk. Reliance on maternal reserves has allowed some large mammals to give birth and lactate at sites and times far removed from food resources.

Complex inter-relationships exist between certain micronutrients, immune function and disease resistance in cattle. Several micronutrients have been shown to influence immune responses. The relationship between deficiencies of some micronutrients and disease resistance is less clear. A number of studies have indicated that Cr supplementation may improve cell-mediated and humoral immune response as well as resistance to respiratory infections in stressed cattle. With respiratory-disease challenge models Cr generally does not affect disease resistance. Deficiencies of Cu, Se, vitamin E and Co in cattle reduce the ability of isolated neutrophils to kill yeast and/or bacteria. Cu deficiency reduces antibody production, but cell-mediated immunity is generally not altered. However, Cu deficiency appears to reduce production of interferon and tumour necrosis factor by mononuclear cells. Numerous studies have linked low vitamin E and/or Se status to increased susceptibility of dairy cows to intramammary infections. In contrast to findings in laboratory animals, marginal Zn deficiency does not appear to impair antibody production or lymphocyte responsiveness to mitogen stimulation in ruminants. Co deficiency has been associated with reduced resistance to parasitic infections. It is well documented that vitamin A-deficient animals are more susceptible to various types of infections. β-Carotene, possibly via its antioxidant properties, may affect immune function and disease resistance independent of its role as a precursor of vitamin A.

Allergic diseases are a common cause of illness in most industrialized countries. Diet during early childhood is an important determinant of the development of allergy, particularly in high-risk infants who have a parental history of atopy. Maternal avoidance of highly-allergenic foods during pregnancy and lactation, prolonged exclusive breast-feeding, the use of a hydrolysed milk formula, and delayed introduction of dairy products, eggs, fish, nuts and soyabean are associated with a lower incidence of allergic symptoms and signs. These beneficial effects are observed for as long as 18 years of age. Similarly, nutrition and physical growth are important factors that influence immunocompetence and morbidity due to infections. Small-for-gestational age low-birth-weight infants show prolonged impairment of cell-mediated immunity, antibody responses and phagocyte function. Recent studies indicate the beneficial effect of moderate amounts of Zn given in the first 6 months of life. Thus, diet and nutrition in early life are crucial for the development of allergic and infectious disease throughout childhood and into adulthood.

Appropriate nutrient partitioning between the maternal body and gravid uterus is essential for optimum fetal growth and neonatal survival, and in adult sheep nutrient partitioning during pregnancy generally favours the conceptus at the expense of the dam. However, recent studies using an overnourished adolescent sheep model demonstrate that the hierarchy of nutrient partitioning during pregnancy can be dramatically altered in young growing females. Overnourishing the adolescent dams to promote rapid maternal growth throughout pregnancy results in a major restriction in placental mass and leads to a significant decrease in birth weight relative to moderately-fed adolescents of equivalent gynaecological age. High maternal feed intakes are also associated with an increased incidence of non-infectious spontaneous abortion, a reduction in gestation length and colostrum production, and a higher incidence of neonatal mortality. The present paper examines the putative role of a variety of endocrine regulators of nutrient partitioning in this unusual model system, where the dam is overnourished while the stunted placenta restricts nutrient supply to the fetus. The central role of nutritionally-mediated alterations in placental growth and development in setting the subsequent pattern of nutrient partitioning between the maternal body, placenta and fetus is examined, and critical periods of sensitivity to alterations in maternal nutritional status are defined. Finally, the consequences of this form of inappropriate nutrient partitioning on the growth and development of the fetus and neonate are described with particular emphasis on the reproductive axis.

The immune system works best if the lymphoid cells have a delicately balanced intermediate level of glutathione. Even moderate changes in the intracellular glutathione level have profound effects on lymphocyte functions. Certain functions, such as the DNA synthetic response, are exquisitely sensitive to reactive oxygen intermediates and, therefore, are favoured by high levels of the antioxidant glutathione. Certain signal pathways, in contrast, are enhanced by oxidative conditions and favoured by low intracellular glutathione levels. The available evidence suggests that the lymphocytes from healthy human subjects have, on average, an optimal glutathione level. There is no indication that immunological functions such as resistance to infection or the response to vaccination may be enhanced in healthy human subjects by administration of glutathione or its precursor amino acid cysteine. However, immunological functions in diseases that are associated with a cysteine and glutathione deficiency may be significantly enhanced and potentially restored by cysteine supplementation. This factor has been studied most extensively in the case of human immunodeficiency virus (HIV)-infected patients who were found to experience, on average, a massive loss of S equivalent to a net loss of approximately 4 g cysteine/d. Two randomized placebo-controlled trials have shown that treatment of HIV-infected patients with N-acetyl-cysteine caused in both cases a significant increase in all immunological functions under test, including an almost complete restoration of natural killer cell activity. It remains to be tested whether cysteine supplementation may be useful also in other diseases and conditions that are associated with a low mean plasma cystine level and impaired immunological functions.

When children and adolescents are the target population in dietary surveys many different respondent and observer considerations surface. The cognitive abilities required to self-report food intake include an adequately developed concept of time, a good memory and attention span, and a knowledge of the names of foods. From the age of 8 years there is a rapid increase in the ability of children to self-report food intake. However, while cognitive abilities should be fully developed by adolescence, issues of motivation and body image may hinder willingness to report. Ten validation studies of energy intake data have demonstrated that mis-reporting, usually in the direction of under-reporting, is likely. Patterns of under-reporting vary with age, and are influenced by weight status and the dietary survey method used. Furthermore, evidence for the existence of subject-specific responding in dietary assessment challenges the assumption that repeated measurements of dietary intake will eventually obtain valid data. Unfortunately, the ability to detect mis-reporters, by comparison with presumed energy requirements, is limited unless detailed activity information is available to allow the energy intake of each subject to be evaluated individually. In addition, high variability in nutrient intakes implies that, if intakes are valid, prolonged dietary recording will be required to rank children correctly for distribution analysis. Future research should focus on refining dietary survey methods to make them more sensitive to different ages and cognitive abilities. The development of improved techniques for identification of mis-reporters and investigation of the issue of differential reporting of foods should also be given priority.

The number of US children who are overweight has more than doubled over the last decade. This change has broadened the focus of dietary guidance for children to address nutrient overconsumption and physical activity patterns. Total fat consumption expressed as a percentage of energy intake has decreased among US children. However, this decrease is largely the result of increased total energy intake in the form of carbohydrates and not necessarily due to decreased fat consumption. The majority of children aged 5–17 years are not meeting recommendations for Ca intakes. Much of this deficit is attributed to changing beverage consumption patterns, characterized by declining milk intakes and substantial increases in soft-drink consumption. On average, US children are not eating the recommended amounts of fruits and vegetables. US adolescents become less active as they get older, and one-quarter of all US children watch 4 h television each day, which is positively associated with increased BMI and skinfold thickness. There is an urgent need in the USA for effective prevention strategies aimed at helping children grow up with healthful eating and physical activity habits to achieve optimal health.

Empirical evidence suggests that prolonged underfeeding of protein to late-pregnant dry cows can have modest negative carry-over effects on milk volume and/or protein yield during early lactation, and may also cause increased incidence of metabolic diseases associated with fatty liver. However, assessment of requirements is hampered by lack of information on relationships between dietary intake of crude protein (N × 6·25) and metabolizable protein supply during late pregnancy, and by incomplete understanding of the quantitative metabolism of amino acids in maternal and conceptus tissues. Inability of the postparturient cow to consume sufficient protein to meet mammary and extra-mammary amino acid requirements, including a significant demand for hepatic gluconeogenesis, necessitates a substantial, albeit transient, mobilization of tissue protein during the first 2 weeks of lactation. Ultimately, much of this mobilized protein appears to be derived from peripheral tissues, especially skeletal muscle and, to a lesser extent, skin, through suppression of tissue protein synthesis, and possibly increased proteolysis. In the shorter term, soon after calving, it is likely that amino acids required for hepatic glucose synthesis are diverted from high rates of synthesis of splanchnic tissue and export proteins, including serum albumin. The prevailing endocrine milieu of the periparturient cow, including major reductions in plasma levels of insulin and insulin-like growth factor-I, together with insulin resistance in peripheral tissues, must permissively facilitate, if not actively promote, net mobilization of amino acids from these tissues.

Numerous dietary treatments that purport to promote something unique for stimulating weight loss have been published. These treatments include fad diets, diets formulated by various commercial slimming clubs, very-low-energy diets (VLCD) and conventional diets. Fad diets may possibly reduce some weight short-term; however, there is no scientific basis to their long-term use. Commercial slimming clubs may be suitable for some individuals but they need to be properly assessed professionally. There are specific guidelines for the use of VLCD, which are only appropriate for short-term use. There is scientific evidence to suggest that conventional diets can produce both short- and long-term weight loss. A successful weight-loss programme depends on a multidisciplinary team approach. Management strategies should be devised for addressing issues such as goals, monitoring, follow-up, relapse and evaluation. Initial assessments should include medical, laboratory and anthropometric data, fitness level and dietary and behavioural attitudes. These results will form the basis of the treatment plan. Frequent visits to the clinic are fundamental in promoting continuing weight loss during the long-term maintenance stage of treatment. The visits should be made worthwhile for the patient. Realistic and attainable goals for diet, exercise and behaviour modification should be made. The diet should have a novel approach and be tailored to the needs of the patient. It should be adequate nutritionally, low in energy and fat. The overall aim should be to promote lifelong changes in lifestyle, improvement in quality of life and health risks.

Certain developments in the agricultural and food sciences have far-reaching implications for society and the environment, which suggest the need to examine their ethical acceptability as a standard component of technology assessment. Such considerations have led to the emergence of a new academic discipline, food ethics. The present paper describes how ethical theory may be applied to the analysis of the impacts of prospective food biotechnologies to assess potential effects on four 'interest groups', i.e. consumers, producers, treated organisms and the biota (fauna and flora). The principles which structure the framework used, i.e. the ethical matrix, are adapted to the field of agriculture and food from those applied in medical ethics. Use of the ethical matrix is illustrated by applying it to the specific case of bovine somatotrophin, the genetically-engineered protein hormone which is injected into lactating cattle to increase their milk yields. Ethical analysis is seen to depend on a number of critical requirements, i.e. scientific data, non-scientific evidence and predictions, suitably-qualified assessors ('competent moral judges'), the 'world-views' of the assessors and application of the precautionary principle to cope with 'uncertainty'.

Changes in the amount and metabolism of adipose tissue (AT) occur in underfed ruminants, and are amplified during lactation, or in fat animals. The fat depot of the tail of some ovine breeds seems to play a particular role in adaptation to undernutrition; this role could be linked to its smaller adipocytes and high sensitivity to the lipolytic effect of catecholamines. Glucocorticoids and growth hormone probably interact to induce teleophoretic changes in the AT responses to adenosine and catecholamines during lactation. Fat mobilization in dry ewes is related both to body fatness and to energy balance. The in vivo β-adrenergic lipolytic potential is primarily related to energy balance, whereas basal postprandial plasma non-esterified fatty acids (NEFA) are related to body fatness, and preprandial plasma NEFA is the best predictor of the actual body lipid loss. Several mechanisms seem to be aimed at avoiding excessive fat mobilization and/or insuring a return to the body fatness homeostatic set point. As well as providing the underfed animal with fatty acids as oxidative fuels, AT acts as an endocrine gland. The yield of leptin by ruminant AT is positively related to body fatness, decreased by underfeeding, β-adrenergic stimulation and short day length, and increased by insulin and glucocorticoids. This finding suggests that the leptin chronic (or acute) decrease in lean (or underfed respectively) ruminants is, as in rodents, a signal for endocrine, metabolic and behavioural adaptations aimed at restoring homeostasis.

Ca is the major mineral in bone, and 99 % of the Ca in the body resides in the skeleton. Skeletal mass is a determinant of risk of fracture in childhood as well as adulthood. Over 40 % of adult peak bone mass is acquired during adolescence. This period is when lifestyle choices, including ensuring adequate dietary Ca, regular weight-bearing exercise and avoiding hormonal insufficiency, are especially important. Current Ca intakes for adolescent females are woefully inadequate.