An ideal diet is one that promotes optimal health and longevity. Throughout history, human societies have developed varieties of dietary patterns based on available food plants and animals that successfully supported growth and reproduction. As economies changed from scarcity to abundance, principal diet-related diseases have shifted from nutrient deficiencies to chronic diseases related to dietary excesses. This shift has led to increasing scientific consensus that eating more plant foods but fewer animal foods would best promote health. This consensus is based on research relating dietary factors to chronic disease risks, and to observations of exceptionally low chronic disease rates among people consuming vegetarian, Mediterranean and Asian diets. One challenge to this consensus is the idea that palaeolithic man consumed more meat than currently recommended, and that this pattern is genetically determined. If such exists, a genetic basis for ideal proportions of plant or animal foods is difficult to determine; hominoid primates are largely vegetarian, current hunter—gatherer groups rely on foods that can be obtained most conveniently, and the archeological record is insufficient to determine whether plants or animals predominated. Most evidence suggests that a shift to largely plant-based diets would reduce chronic disease risks among industrialized and rapidly industrializing populations. To accomplish this shift, it will be necessary to overcome market-place barriers and to develop new policies that will encourage greater consump-tion of fruits, vegetables and grains as a means to promote public health.

Fundamental changes in the global structure of food demand will lead to an extra-ordinary increase in the importance of developing countries in global food markets. Economic growth in developing countries is changing consumption patterns, with slower growth (and in many countries actual declines) in per capita food consumption of grains and rapidly growing per capita and total meat consumption, combined with induced growth in cereal feed consumption. The present paper examines the hypothesis, suggested by some researchers, that high-meat diets in developed countries limit improvement in food security in developing countries. These analysts argue that reduced meat consumption in developed countries would release cereals from livestock feed to food for poorer populations, thus improving food security in developing countries. Using the International Food Policy Research Institute (Washington, DC, USA) global food projections model, the international model for policy analysis of agricultural com-modities and trade (see Rosegrant et al. 1995), we first analyse the implications for future global cereal and meat supply and demand resulting from changes in global income, population growth and other structural changes, then simulate alternative sce-narios to examine the effect of large reductions in meat consumption in developed coun-tries on food consumption and food security in developing countries. The paper shows that while the long-term prospects for food supply, demand and trade indicate a strength-ening of world cereal and livestock markets, the improvement in food security in the developing world will be slow, and changes in the dietary patterns in developed countries are not an effective route to improvement in food security in developing countries.

Fe seems to be the only nutrient deficiency that industrialized and low-income countries have in common. Thus, Fe is one of the most critical nutrition requirements to be met in most diets in human subjects. Fe deficiency is caused not only by too low an intake, but is also the result of low bioavailability, as well as an increased Fe requirement due to physiological variables or clinical problems which are not met by an increased dietary intake of Fe. In low-income countries poor dietary quality rather than Fe intake seems to be the key determinant of impaired Fe status. Sometimes the Fe intake even exceeds that in populations of industrialized countries. The interaction of all enhancers (e.g. ascorbic acid and meat), as well as inhibitors (such as bran, polyphenols, egg yolk, soyabean products, Ca, Ca3(PO4)2 and phytic acid (or phytate)) is what determines the bioavailability of non-haem-Fe in the meal. Dietary composition seems to be particularly important when Fe reserves are low, or in the presence of Fe deficiency. Furthermore, the development of anaemia as a result of Fe deficiency, secondary to Fe-stress situations, is dependent on the Fe balance in the host. With respect to the dietary intake of Fe, other products in the food consumed as well as previous treatment of the product (e.g. heat treatment and processing) may also influence bioavailability. Despite all efforts to counteract Fe deficiency it still represents one of the dominant problems in the micronutrient sphere. It is apparent that there is no simple solution to the problem, and the fact that Fe deficiency still occurs in affluent societies consuming a mixed diet speaks for itself; a more holistic view of total dietary composition and the role of enhancers and inhibitors is needed.

Up to 80 % of breast, bowel and prostate cancers are attributed to dietary practices, and international comparisons show strong positive associations with meat consumption. Estimates of relative risk obtained from cohort investigations are in the same direction, although generally weak, and red and processed meats rather than white meat seem to be associated with elevated risk of colon cancer. In breast cancer, there are consistent associations with total meat intake and there is evidence of a dose response. Despite these associations with meat, existing studies suggest that vegetarians do not have reduced risk of breast, bowel or prostate cancer, but there are no quantitative estimates of amounts of meat consumed by meat eaters in these cohort studies. Possible mecha-nisms underlying epidemiological associations include the formation of heterocyclic amines in meat when it is cooked. These heterocyclic amines require acetylation by P450 enzymes, and individuals with the fast-acetylating genotype who eat high amounts of meat may be at increased risk of large-bowel cancer. NH3 and N-nitroso compounds (NOC) formed from residues by bacteria in the large bowel are probably also important. NH3 is a promotor of large-bowel tumours chemically induced by NOC, and some of the chromosomal mutations found in human colo-rectal cancer are consistent with effects of NOC and heterocyclic amines. However, the type, amount, and cooking method of meat or protein associated with increased risk are not certain. The effects of high levels of meat on NH3 and NOC output are not reduced by increasing the amount of fermenta-ble carbohydrate in the diet, but interaction between meat, NSP and vegetable intakes on the risk of cancer has not been studied comprehensively. The interaction between dietary low-penetrance genetic polymorphic and somatic mutation factors has also been investigated to a limited extent. Current Department of Health (1998) recommendations are that meat consumption should not rise, and that consumers at the top end of the distribution should consider a reduction in intakes.

The adequacy of plant-based diets in developed and developing countries as sources of protein and amino acids for human subjects of all ages is examined. Protein quantity is shown not to be an issue. Digestibility is identified as a problem for some cereals (millet (Panicum miliaceum) and sorghum (Sorghum sp.)) and generally is poorly understood. Direct measurements of biological value in children are reviewed and scoring is consid-ered. Various existing requirement values for amino acids and especially lysine are reviewed, and it is concluded that stable-isotope studies do not yet provide adequate alternative values to N balance data, which for lysine are robust after recalculation and adjustment. A new maintenance requirement pattern is developed, with higher values than those of Food and Agriculture Organization/World Health Organization/United Nations University (1985) but lower values than the Massachusetts Institute of Technol-ogy pattern (Young et al. 1989). Calculations of age-related amino acid requirements are based on most recent estimates of human growth and maintenance protein requirements, a tissue amino acid pattern and the new maintenance amino acid pattern. These values appear valid when used to score plant proteins, since they indicate values similar to or less than the biological value measured directly in young children. When used to score plant-based diets in India, no marked deficiencies are identified. All regions score > 1 for adults, whilst for children scores range from > 1, (Tamil Nadhu) from 6 months of age to 0.78 (West Bengal), rising to 0.9 in the 2–5 year old, consistent with reports that high-lysine maize supports similar weight and height growth to that of casein. Inadequate amino acid supply is not an issue with most cereal-based diets.

In early epidemiological studies of diet and cancer the stress was on the search for causal factors. Population (ecological) studies tended to show a strong correlation between meat intake, particularly red meat, and the risk of colo-rectal cancer. They also tended to show meat to be strongly inversely correlated with cancers of the stomach and oesophagus and liver. Early case- control studies tended to support the postulated role for red meat in colo-rectal carcinogenesis, although more recent case-control studies, particularly those from Europe, have tended to show no relationship. The cohort studies in general failed to detect any relationship between meat intake and colo-rectal cancer risk. The available evidence points to the intake of protective factors such as vegetables and whole-grain cereals being the main determinants of colo-rectal cancer risk, with meat intake only coincidentally related.

The nutritional adequacy of plant-based diets is discussed. Energy and protein intakes are similar for plant-based diets compared with those containing meat. Fe and vitamin B12 are the nutrients most likely to be found lacking in such diets. Bioactive substances present in foods of plant origin significantly influence the bioavailability of minerals and requirements for vitamins. Well-balanced vegetarian diets are able to support normal growth and development. It is concluded that meat is an optional rather than an essential constituent of human diets.

Compared with non-vegetarians, Western vegetarians have a lower mean BMI (by about 1 kg/m2), a lower mean plasma total cholesterol concentration (by about 0.5 mmol/l), and a lower mortality from IHD (by about 25 %). They may also have a lower risk for some other diseases such as constipation, diverticular disease, gallstones and appendicitis. No differences in mortality from common cancers have been established. There is no evidence of adverse effects on mortality. Much more information is needed, particularly on other causes of death, other morbidity including osteoporosis, and long-term health in vegans. The evidence available suggests that widespread adoption of a vegetarian diet could prevent approximately 40 000 deaths from IHD in Britain each year.

The prevalence of obesity in children, as in adults, is increasing dramatically. The extent to which this is due to reduced energy expenditure, increased energy intake, or both, is unclear at present. This in part reflects the limitations of existing models of the pre-obese state. In childhood acute lymphoblastic leukaemia (ALL), patients typically gain weight excessively during and after 2 years of therapy, and are at high risk of becoming obese. Previous studies have failed to identify the cause of obesity in these patients. We have tested the hypothesis that excess weight gain in ALL is due to reduced total energy expenditure (TEE), measured using the doubly-labelled water method, and have identified risk factors for excess weight gain in ALL. Pre-obese children with ALL in the dynamic phase of weight gain are less physically active than their peers, with a reduced TEE of approximately 1.2 (95 % CI 0.2, 2.2) MJ/d. While other factors might contribute to excess weight gain, lifestyle (i.e. reduced habitual physical activity) plays a central role in ALL. Several considerations suggest that ALL might be a useful model of the pre-obese state: lifestyle is critical to development of obesity in ALL; ALL is relatively common; approximately 70 % of patients survive; patients are readily accessible during the 2 years of therapy and beyond.

Placental weight is a primary factor determining size at birth in many species. In sheep, placental weight peaks at approximately mid-gestation, with structural remodelling occurring over the second half of pregnancy to meet the increasing nutritional demands of the growing fetus. Numerous factors influence placental growth and development in sheep, and many workers (see Kelly, 1992) have investigated the role of maternal nutrition as a regulator of placental and fetal size. We have studied the effects of feeding ewes approximately 50 % of their recommended energy requirements during early to mid-pregnancy on fetal and placental indices measured at mid-gestation (i.e. 80 d) and close to term (i.e. 145 d). Maternal nutrient restriction is associated with a reduction in placental weight at 80 d, but an increase in placental weight at 145 d of gestation, compared with ewes fed adequately in early pregnancy. No significant effect on fetal weight was observed at either 80 or 145 d gestation, although differences in body dimensions and the insulin-like growth factor-1 axis were found in lambs from nutrient-restricted ewes delivered close to term. Maternal nutrition during pregnancy plays a pivotal role in the regulation of fetal and placental development in sheep, and therefore has the potential to influence both short- and longer-term health outcomes.

Vitamin A is the generic term for a variety of fat-soluble substances including retinol, retinyl palmitate and the provitamin A carotenoids such as all-trans-β-carotene. Vitamin A is commonly known as the anti-infective vitamin and has an essential role in vision and cellular differentiation, the latter providing a unique core mechanism helping to explain the influence of vitamin A on epithelial barriers. Alterations in the epithelial lining of vital organs occur early in deficiency, suggesting a potentially important role for the barrier function. Vitamin A deficiency (VAD) is most commonly recognized in the eye. The conjunctival-impression cytology test detects the presence of larger irregular keratinized cells and the absence of mucous-secreting goblet cells, indicative of VAD. The method is simple, quick and sensitive in populations where VAD is present. In the respiratory tract, observational studies all show an association with VAD, although vitamin A supplementation studies appear to have little effect on respiratory disease. Organ-specific targeting may improve success rates. The dual-sugar intestinal-permeability test allows the effect of vitamin A supplementation to be monitored on the gastrointestinal tract. Two vitamin A supplementation studies were carried out recently in Orissa State, India. Healthy infants of weaning age were administered orally eight weekly doses of 5.0 mg retinol equivalents and hospitalized infants received one large oral dose 60 mg retinol equivalents in the form of retinyl palmitate. Improvements in gut integrity and haematological status were observed in both studies. In summary, the response of the eye to vitamin A supplementation is well established; the present review highlights some of the more recent observations examining the effects of vitamin A.

While many experimental studies have shown a protective effect of vitamin C in age-related cataract, other studies have revealed contrasting roles for this nutrient. Oxidative damage in the lens can be prevented by vitamin C. However, a pro-oxidant effect of vitamin C through H2O2 generation has been suggested. Vitamin C has also been shown to play a role in protein glycation, which is observed in cataract formation. A protective effect of dietary energy restriction appears to be inversely related to plasma vitamin C levels in rodents. Moreover, conclusions from human epidemiological and intervention studies are not uniform. The available evidence suggests that maintenance of sufficient plasma vitamin C is needed to prevent oxidative damage in the lens. More research will be needed in order to confirm the relative importance of the different roles of vitamin C in the eye lens.

There is an increasing interest in the relationship between nutrition and lung health. Epidemiological studies suggest that dietary habits may have an influence on lung function and the tendency to common lung diseases such as asthma, chronic obstructive pulmonary disease (COPD) and lung cancer. In particular, a diet rich in fresh fruit and fish has been associated with a salutary effect on lung health. End-stage COPD is associated with a state of nutritional depletion which is refractory to conventional nutritional supplementation. In contrast, malnutrition associated with cystic fibrosis is amenable to nutritional therapy, which has been shown to improve prognosis in this disease.

The epidemiological evidence for a relationship between diet and indicators of asthma and chronic obstructive pulmonary disease (COPD) is evaluated. The review focuses on the intake of Na, n−3 fatty acids, and antioxidant vitamins as well as fruit and vegetables. Experimental studies suggest that a high-Na diet has a small adverse effect on airway reactivity in asthma patients. However, observational studies provide no clear evidence that high Na intake has adverse effects on airway reactivity or asthma symptoms in open populations. n−3 Polyunsaturated fatty acids, which are present in fish oils, are metabolized into less broncho-constricting and inflammatory mediators than n−6 polyunsaturated fatty acids. Studies in the general adult population suggest that a high fish intake has a beneficial effect on lung function, but the relationship with respiratory symptoms and clinically-manifest asthma or COPD is less evident. Also, experimental studies in asthma patients have not demonstrated an improvement in asthma severity after supplementation with fish oil. Several studies showed a beneficial association between fruit and vegetable intake and lung function, but the relationship with respiratory symptoms and the clinically-manifest disease was less convincing. A similar pattern was found for vitamin C in relation to indicators of asthma and COPD, but there are still conflicting results with respect to vitamin E and β-carotene. In conclusion, the epidemiological evidence for a beneficial effect on indicators of asthma and COPD of eating fish, fruit and vegetables is increasing. However, the effectiveness of dietary supplementation in open-population samples is often not demonstrated. Several unresolved questions are raised, which should be addressed in future studies on the relationship between diet and respiratory disease.

The present paper reviews current knowledge of the pulmonary cachexia syndrome with reference to chronic obstructive pulmonary disease (COPD). Aspects of incidence, aetiology and management are discussed. Malnutrition occurs in approximately one-quarter to one-third of patients with moderate to severe COPD. Both fat mass and fat-free mass become depleted. Loss of fat-free mass is the more important and appears to be due to a depression of protein synthesis. Weight loss is an independent prognostic indicator of mortality, and is associated with increased morbidity and decreased health-related quality of life. The aetiology of malnutrition in COPD is not well understood. Reduced food intake does not seem to be the primary cause. Resting energy expenditure (REE) is elevated in a proportion of patients and probably contributes to negative energy balance. Measurement of actual REE is helpful when considering the adequacy of nutritional supplementation. The underlying reason for a hypermetabolic state is not known. Although weight-losing COPD patients are not catabolic, nutritional supplementation alone does not appear to reverse the loss of fat-free mass. Strategies involving nutritional supplementation in combination with a second intervention are being explored, and there are some encouraging results using anabolic hormones.

Lung cancer is the most common cancer in the world, and smoking is the major risk factor, accounting for about 90% of the cases. Diet has also been implicated in the development of lung cancer, although the specific nutrients remain to be elucidated. Vitamins with antioxidant activity have received much attention. β-Carotene, the most efficient provitamin A, was found to be inversely related to the risk of lung cancer in many prospective epidemiological studies, especially in studies measuring serum concentrations of β-carotene. The findings from controlled trials, however, contradict the hypothesis that β-carotene could prevent lung cancer, but rather suggest increased risk of lung cancer with supplementary β-carotene. Data from both prospective studies and a controlled trial suggest no role for vitamin E in lung carcinogenesis. Some prospective epidemiological studies suggest an inverse relationship between dietary vitamin C and the risk of lung cancer, but due to the high correlation between dietary vitamin C and vegetable and fruit intake the independent role of dietary vitamin C is difficult to estimate. Studies using prediagnostic plasma concentrations of ascorbic acid do not support the involvement of vitamin C in lung carcinogenesis, and no controlled trials of vitamin C on lung cancer have been published. Thus, supplementation with antioxidant vitamins cannot be recommended for the prevention of lung cancer. Non-smoking is the most important target in the prevention of lung cancer. High i ntakes of vegetables and fruits may provide additional protection and are unlikely to be harmful.

The present paper explores possible implications of the globalization of the food system for diet and health. The paper poses five key questions to clarify the relationship between food and globalization. The first question is what is globalization. The paper suggests that it is helpful to distinguish between economic, political, ideological and cultural processes. Globalization is also marked by internal oppositional dynamics: there are re-localization and regional tendencies which counter the global. The second question is whether there is anything new about globalization. Food has been a much traded commodity for millennia. The paper concludes that what is new about the current phases of globalization is the pace and scale of the change, and the fact that power is being concentrated into so few hands. New marketing techniques and supply-chain management consolidate these features. The third question is who is in control of the globalization era and who benefits and loses from the processes of globalization. It is argued that modern food economies are hypermarket rather than market economies, with power accruing to the distributor more than has been recognized. The fourth question concerns governance of the food system. Historically, systems of local and national government have regulated the food supply where appropriate. Now, new international systems are emerging, partly using existing bodies and partly creating new ones. The final question is of the future. Globalization is a value-laden area of study, yet its implications for dietary change and for health are considerable. The paper argues that dimensions of change can be discerned, although it would be rash to bet on which end of each dimension will emerge as dominant in the 21st century.

In 1996 the population of China reached 1.23 billion, 22 % of the world population, and is expected to increase to 1.5 billion by 2020. As China has only 7 % of the world's arable land such population increases are likely to have an important impact on food supply in China and the world. Projections of the potential impact are discussed. The restructuring of Chinese agriculture at the end of the 1970s has led to dramatic increases in agricultural production and food consumption, in particular of animal products, fruit and vegetables. Along with these rapid changes there is evidence of a nutrition transition in which diseases associated with affluence are becoming more prevalent than deficiency diseases. This transition has led to concern about the evolving dietary pattern. The replacement of legumes, including soyabean, by meat and other animal products as rich sources of protein and other nutrients has been controversially argued on grounds of nutritional health, ecological impact, economic effects and world food supply. These arguments are reviewed and the pressures internal and external to China concerning the production and consumption of animal v. legume products are presented. It is concluded that nutritional policies to promote the consumption of soyabean are unlikely to be effective in the context of an increasingly free and global market.

As disasters and conflict increase, a higher proportion of total food aid is given as humanitarian aid. Most food aid is in the form of cereals, primarily wheat. The main donors are the USA and the EU, but there is an increase in the numbers of donors, including non-governmental organizations, buying food rather than using surpluses. Alongside the greater diversity and complexity of food aid, there is more controversy about policy and practice. If disasters are development failures, emergency food aid must be a step in the continuum from relief to rehabilitation. Comparisons of the seventeen countries that were major recipients of food aid (> 10 000 t) in 1997, show diversity in social development, dietary pattern, number of refugees, relative food inadequacy and wasting (i.e. % standard weight-for-height > 2 SD). In the absence of information of consistent quality, what influences the scale of emergency aid is unclear and susceptible to politicization, so that need and supply may not be matched. Local considerations seem to be as important as external food aid for the nutrition of the recipients. Challenges for the future include assuring the nutritional quality of rations to solve deficiency problems. The implications for the professional public health nutritionist working on emergency food provision include continuing professional development to enhance the technical expertise necessary to design appropriate feeds or rations. These public health nutritionists, more than others, require a grounding in social science theories that underpin management, ethics of professionalism and the politics of food aid.