Measurement of dietary exposure: a challenging problem which may be overcome thanks to metabolomics?

The diet is an important environmental exposure, and its measurement is an essential component of much health-related research. However, conventional tools for measuring dietary exposure have significant limitations being subject to an unknown degree of misreporting and dependent upon food composition tables to allow estimation of intakes of energy, nutrients and non-nutrient food constituents. In addition, such tools may be inappropriate for use with certain groups of people. As an alternative approach, the recent techniques of metabolite profiling or fingerprinting, which allows simultaneous monitoring of multiple and dynamic components of biological fluids, may provide metabolic signals indicative of food intake. Samples can be analysed through numerous analytical platforms, followed by multivariate data analysis. In humans, metabolomics has been applied successfully in pharmacology, toxicology and medical screening, but nutritional metabolomics is still in its infancy. Biomarkers of a small number of specific foods and nutrients have been developed successfully but less targeted and more high-throughput methods, that do not need prior knowledge of which signals might be discriminatory, and which may allow a more global characterisation of dietary intake, remain to be tested. A proof a principle project (the MEDE Study) is currently underway in our laboratories to test the hypothesis that high-throughput, non-targeted metabolite fingerprinting using flow injection electrospray mass spectrometry can be applied to human biofluids (blood and urine) to characterise dietary exposure in humans.     

Iodine uptake and loss-can frequent strenuous exercise induce iodine deficiency?

Most of the daily dietary iodine intake (approximately 90 %) will be excreted in the urine; measurement of urinary iodine excretion is thus routinely used as an index of dietary iodine intake. However, urinary excretion is not the only means of iodine loss. Subjects such as athletes or those participating in vigorous exercise can lose a considerable amount of iodine in sweat, depending on environmental factors such as temperature and humidity. In areas of lower to moderate dietary iodine intake, loss in sweat can equal that in urine. Although electrolyte loss in sweat is well-recognized and replacement strategies are adopted, there is less recognition of potential iodine loss. Crude calculations reveal that if sweat iodide losses are not replaced, dietary stores could be depleted in an athlete undergoing a regular training regime. The significance of these losses could be increased in areas where dietary iodine intake is lower in the summer months. Although there is little doubt that excessive sweating can induce a relative iodine deficiency state, there is no case as yet for iodine supplementation in those that take vigorous exercise. However, sustained iodine loss may have implications for thyroid status and possibly consequences for athletic performance.     

Linear measurement error models with restricted sampling

The relationship between nutrient consumption and chronic disease risk is the focus of a large number of epidemiological studies where food frequency questionnaires (FFQ) and food records are commonly used to assess dietary intake. However, these self-assessment tools are known to involve substantial random error for most nutrients, and probably important systematic error as well. Study subject selection in dietary intervention studies is sometimes conducted in two stages. At the first stage, FFQ-measured dietary intakes are observed and at the second stage another instrument, such as a 4-day food record, is administered only to participants who have fulfilled a prespecified criterion that is based on the baseline FFQ-measured dietary intake (e.g., only those reporting percent energy intake from fat above a prespecified quantity). Performing analysis without adjusting for this truncated sample design and for the measurement error in the nutrient consumption assessments will usually provide biased estimates for the population parameters. In this work we provide a general statistical analysis technique for such data with the classical additive measurement error that corrects for the two sources of bias. The proposed technique is based on multiple imputation for longitudinal data. Results of a simulation study along with a sensitivity analysis are presented, showing the performance of the proposed method under a simple linear regression model.     

Binary regression in truncated samples, with application to comparing dietary instruments in a large prospective study

Summary .   We examine two issues of importance in nutritional epidemiology: the relationship between dietary fat intake and breast cancer, and the comparison of different dietary assessment instruments, in our case the food frequency questionnaire (FFQ) and the multiple-day food record (FR). The data we use come from women participants in the control group of the Dietary Modification component of the Women's Health Initiative (WHI) Clinical Trial. The difficulty with the analysis of this important data set is that it comes from a truncated sample, namely those women for whom fat intake as measured by the FFQ amounted to 32% or more of total calories. We describe methods that allow estimation of logistic regression parameters in such samples, and also allow comparison of different dietary instruments. Because likelihood approaches that specify the full multivariate distribution can be difficult to implement, we develop approximate methods for both our main problems that are simple to compute and have high efficiency. Application of these approximate methods to the WHI study reveals statistically significant fat and breast cancer relationships when a FR is the instrument used, and demonstrate a marginally significant advantage of the FR over the FFQ in the local power to detect such relationships.     

Diet quality and the attractiveness of male body odor

Human axillary sweat may provide information pertaining to genetic relatedness and health status. A significant contributor to good health, both in the short and longer term, is a diet rich in fruit and vegetables. In this study we tested whether dietary fruit and vegetable intake, assessed indirectly by skin spectrophotometry (assessing dietary carotenoid intakes) and subjectively by food frequency questionnaire, was associated with more pleasant smelling sweat. Male participants provided axillary sweat samples and dietary information. Female participants then evaluated these samples on several affective, qualitative and psychophysical dimensions. The skin spectrophotometry measure (CIELab b*), indicative of greater fruit and vegetable intake, was significantly associated with more pleasant smelling sweat (with more floral, fruity, sweet and medicinal qualities), independent of sweat intensity. Self-report dietary data revealed that fat, meat, egg and tofu intake was associated with more pleasant smelling sweat, and greater carbohydrate intake with stronger smelling less pleasant sweat. These data parallel facial judgments, in which yellower more carotenoid rich skin, is found to be more attractive.     

Metagenomics in animal gastrointestinal ecosystem: Potential biotechnological prospects

Microbial metagenomics---the applications of the genomics suit of technologies to nonculturable microorganisms, is coming of age. These approaches can be used for the screening and identification of nonculturable gastrointestinal (GI) microflora for assessing and exploiting them in nutrition and the health of the host. Advances in technologies designed to access this wealth of genetic information through environmental nucleic acids extraction and analysis have provided the means of overcoming the limitations of conventional culture-dependent microbial genetic exploitation. The molecular techniques and bioinformatics tools will result in reliable insights into the animals' GI microbial structure and activity of the livestock gut microbes in relation to functional interactions, temporal and spatial relationships among different microbial consortia and dietary ingredients. Further developments and applications of these methods promise to provide the opportunity to link distribution and identity of various GI microbes in their natural habitats, and explore their use for promoting livestock health and industrial development.     

Limited-protein diet: a means of delaying the progression of chronic renal disease?

Recent studies suggest that restricting the dietary protein intake of patients with progressive renal disease slows their loss of renal function. Studies in animals have shown that an increase in the filtration rates of individual nephrons (hyper-filtration), an adaptive response to loss of renal mass, appears to induce progressive renal damage and that such damage may be prevented by dietary protein restriction. Preliminary evidence suggests that restriction of protein intake to less than 50 g/d in man has a similar beneficial effect in slowing the progression of chronic renal disease. Dietary therapy appears to be particularly effective for patients with early renal disease, allowing a doubling in the time until dialysis is required in many cases. Although large-scale clinical studies are planned, there is now sufficient evidence to warrant the use of moderate protein restriction (to less than 50 g/d) in most patients suffering from progressive renal disease. Such therapy should only be instituted with expert dietary and nephrologic consultation.     

Overview of marker vaccine and differential diagnostic test technology.

Recent advances in molecular biology, immunology, microbiology, genetics and microbial pathogenesis have lead to the development of a wide variety of new approaches for developing safer and more effective vaccines based on designs such as subunit vaccines, gene deleted vaccines, live vectored vaccines, and DNA mediated vaccines. Technology tools can be as basic as identifying naturally occurring strains with deletions that support differentiating infected from vaccinated animal (DIVA) needs or be based on higher technology developments such as improved protein expression and purification methods, transgenic plant- and plant virus-based antigen production, and novel adjuvants that target specific immune responses. These new approaches, when applied to the development of marker vaccines and companion diagnostic test kits hold tremendous potential for developing improved tools for eradication and control programs. Marker vaccines and companion diagnostic test kits must meet the established licensing requirements for purity, potency, safety and efficacy. Efficacy claims are based on evaluation of the level of protection demonstrated in host animal trials and may range from "prevents infection with (a specific agent)", to "for use as an aid in the reduction of disease due to (a specific agent)." The differences in claims and recommendations are a function of the variation in protection elicited by various vaccines. For designing effective eradication programs, vaccine efficacy characteristics such as for reducing susceptibility to infections and spread of infections must be well defined; similarly, diagnostic test performance characteristics (efficacy) must be determined. In addition to data to support efficacy claims, it is imperative that safety of production and use of vaccines be evaluated. During the design of marker vaccines and diagnostic tests, it is important to consider the application of appropriate technologies to improve the safety of these products. Use of recombinant technologies for production of vaccines and/or diagnostic test antigens can reduce the biosafety concerns during production and during use, including human exposure to zoonotic pathogens during production and use, and potential spread of foreign animal disease agents due to loss of biocontainment. In addition, vaccines may induce adverse reactions. It is important to determine the frequency of adverse events and to reduce the likelihood of induction of adverse reactions through proper design.     

Evaluation of methods used to assess dietary intake: simulation analyses

The choice of dietary methodology can affect the ability to detect and describe the relationship between dietary sodium intake and blood pressure. This is illustrated in this paper through the use of simulation modelling of the effect of using different dietary methods (food recalls or records covering different numbers of days, food frequency questionnaire estimates of a single diet component) and using urinary excretion as a proxy for intake. Both epidemiologic studies and experimental interventions are simulated. Although the data base used was simulated rather than real, an attempt was made to keep it realistic in relation to what might be seen in actual populations. From these analyses it can be inferred that with appropriate choice of methodology and study design, even low order relationships between sodium intake and blood pressure should be detectable. At a more general level, it may be concluded that while there is no perfect dietary methodology, there are preferred methodologies for defined purposes.     

Virus-host interactomes and global models of virus-infected cells

Novel high-throughput technologies such as yeast two-hybrid and RNA interference (RNAi) screens provide the tools to study interactions between viral proteins and the host on a genomic scale. In this review, we provide an overview of studies in which these technologies were applied and of computational approaches for the analysis of the identified viral interactors in the context of the host cell. The results of these studies illustrate the advantages of integrative systems biology approaches in the investigation of viral pathogens.     

Biomarkers in nutritional epidemiology: applications, needs and new horizons

Modern epidemiology suggests a potential interactive association between diet, lifestyle, genetics and the risk of many chronic diseases. As such, many epidemiologic studies attempt to consider assessment of dietary intake alongside genetic measures and other variables of interest. However, given the multi-factorial complexities of dietary exposures, all dietary intake assessment methods are associated with measurement errors which affect dietary estimates and may obscure disease risk associations. For this reason, dietary biomarkers measured in biological specimens are being increasingly used as additional or substitute estimates of dietary intake and nutrient status. Genetic variation may influence dietary intake and nutrient metabolism and may affect the utility of a dietary biomarker to properly reflect dietary exposures. Although there are many functional dietary biomarkers that, if utilized appropriately, can be very informative, a better understanding of the interactions between diet and genes as potentially determining factors in the validity, application and interpretation of dietary biomarkers is necessary. It is the aim of this review to highlight how some important biomarkers are being applied in nutrition epidemiology and to address some associated questions and limitations. This review also emphasizes the need to identify new dietary biomarkers and highlights the emerging field of nutritional metabonomics as an analytical method to assess metabolic profiles as measures of dietary exposures and indicators of dietary patterns, dietary changes or effectiveness of dietary interventions. The review will also touch upon new statistical methodologies for the combination of dietary questionnaire and biomarker data for disease risk assessment. It is clear that dietary biomarkers require much further research in order to be better applied and interpreted. Future priorities should be to integrate high quality dietary intake information, measurements of dietary biomarkers, metabolic profiles of specific dietary patterns, genetics and novel statistical methodology in order to provide important new insights into gene-diet-lifestyle-disease risk associations.     

Hormones in meat: different approaches in the EU and in the USA

The use of hormonal active growth promoters ("hormones") in farm animals can increase the production of veal and beef significantly up to 15%. However, in the different parts of the world the regulation regarding the use of such hormones differs sharply. In the European Union there exists a total ban on such use in contrast to the United States of American where the use of some hormones is authorized under strict conditions. An overview is given of the different opposing aspects and their consequences are discussed. It has to be concluded that in some EU Member States an extended black market exists. For the USA no experimental evidence is available for such a black market. In the EU the number of ascertained different illegal "hormones" ranges between about 35 and 55. In the USA the number of legal hormones in total is six. The levels of hormone residues found in beef originating from the USA are in the fast majority of cases below the Maximum Residue Limit as recommended by the FAO/WHO Joint Expert Committee of Food Additives. No comparable experimental data are available for the EU. Finally other food commodities have to be taken into account to assess potential risks of the dietary intake of "hormones". Eggs, example given, contribute more to the dietary intake of estradiol than beef, whether the animal is legally treated with hormones or not.     

Fatty acid composition of adipose tissue and blood in humans and its use as a biomarker of dietary intake

Accurate assessment of fat intake is essential to examine the relationships between diet and disease risk but the process of estimating individual intakes of fat quality by dietary assessment is difficult. Tissue and blood fatty acids, because they are mainly derived from the diet, have been used as biomarkers of dietary intake for a number of years. We review evidence from a wide variety of cross-sectional and intervention studies and summarise typical values for fatty acid composition in adipose tissue and blood lipids and changes that can be expected in response to varying dietary intake. Studies in which dietary intake was strictly controlled confirm that fatty acid biomarkers can complement dietary assessment methodologies and have the potential to be used more quantitatively. Factors affecting adipose tissue and blood lipid composition are discussed, such as the physical properties of triacylglycerol, total dietary fat intake and endogenous fatty acid synthesis. The relationship between plasma lipoprotein concentrations and total plasma fatty acid composition, and the use of fatty acid ratios as indices of enzyme activity are also addressed.     

Application of mass spectrometry to the discovery of biomarkers for detection of prostate cancer

There has been an impressive emergence of mass spectrometry based technologies applied toward the study of proteins. Equally notable is the rapid adaptation of these technologies to biomedical approaches in the realm of clinical proteomics. Concerted efforts toward the elucidation of the proteomes of organ sites or specific disease state are proliferating and from these efforts come the promise of better diagnostics/prognostics and therapeutic intervention. Prostate cancer has been a focus of many such studies with the promise of improved care to patients via biomarkers derived from these proteomic approaches. The newer technologies provide higher analytical capabilities, employ automated liquid handling systems, fractionation techniques and bioinformatics tools for greater sensitivity and resolving power, more robust and higher throughput sample processing, and greater confidence in analytical results. In this prospects, we summarize the proteomic technologies applied to date in prostate cancer, along with their respective advantages and disadvantages. The development of newer proteomic strategies for use in future applications is also discussed.     

Vitamin D in foods and as supplements

Numerous studies have shown that the vitamin D status is far from optimal in many countries all over the world. The main reason for this is lack of sunshine. Only a limited number of foods naturally contain vitamin D. Good sources of vitamin D(3) are fish (not only fatty fish), egg yolk, and offal such as liver. Some foods such as milk are fortified with vitamin D in some countries. Dietary vitamin D intake is low in many countries, especially as the dietary sources are limited. The use of supplements is important and seems to be high in some countries. Current dietary intake recommendations are too low to preserve/reach optimal S-25-OHD concentrations, when UVB radiation is not available. We suggest that the recommendations should be increased to at least 10 microg per day in all age groups when solar UVB is scarce. The elderly may need a daily vitamin D intake of 25 microg. If dietary intake of vitamin D is to be increased, food habits will have to change. From a public health point of view it is better to increase the potential sources of vitamin D by fortifying specific products that are consumed commonly in a whole population, or if necessary by especially vulnerable groups. Supplement use is probably the right alternative for vulnerable groups such as infants and inactive elderly in whom this is more easily implemented.     

Cost-effectiveness of interventions to promote fruit and vegetable consumption

Background

Fruits and vegetables are an essential part of the human diet, but many people do not consume the recommended serves to prevent cardiovascular disease and cancer. In this research, we evaluate the cost-effectiveness of interventions to promote fruit and vegetable consumption to determine which interventions are good value for money, and by how much current strategies can reduce the population disease burden.

Methods/Principal Findings

In a review of published literature, we identified 23 interventions for promoting fruit and vegetable intake in the healthy adult population that have sufficient evidence for cost-effectiveness analysis. For each intervention, we model the health impacts in disability-adjusted life years (DALYs), the costs of intervention and the potential cost-savings from averting disease treatment, to determine cost-effectiveness of each intervention over the lifetime of the population, from an Australian health sector perspective. Interventions that rely on dietary counselling, telephone contact, worksite promotion or other methods to encourage change in dietary behaviour are not highly effective or cost-effective. Only five out of 23 interventions are less than an A$50,000 per disability-adjusted life year cost-effectiveness threshold, and even the most effective intervention can avert only 5% of the disease burden attributed to insufficient fruit and vegetable intake.

Conclusions/Significance

We recommend more investment in evaluating interventions that address the whole population, such as changing policies influencing price or availability of fruits and vegetables, to see if these approaches can provide more effective and cost-effective incentives for improving fruit and vegetable intake.