Progress in food & nutrition science最新文献

The renewed interest in fish and fish oil has led to a re-examination of the biochemical and physiological basis of the preventive and therapeutic effects of fish and its components. Fatty acids are produced by a complex synthetic process. Unsaturated fatty acid derived from dietary sources are required for eicosanoid formation and are an integral part of cell wall and mitochondrial membranes. The beneficial role of fish oils is believed to stem from their being rich sources of omega-3 fatty acids. The dietary requirement of these fatty acids is a controversial issue but their essentiality for human health is being increasingly demonstrated and recognized. This review focusses on general aspects of lipid metabolism, biochemistry and physiological role of omega-3 fatty acids, and the unique characteristics of fatty acids found in fish. A subsequent review article will deal with metabolic and clinical aspects.

A model has been developed to describe zinc metabolism in humans. The model was developed from a series of studies in normal volunteers and patients with various clinical disorders. Zinc metabolism was studied with radiotracers for 9-12 mo before and after a daily oral zinc load of 100 mg. Data were analysed by compartmental analysis and a model was developed that consists of compartments for zinc in the gut, plasma, red blood cells, liver, muscle, bone and other tissues with excretion via urine and feces. Using the model parameters of zinc metabolism including absorption, tissue exchange, secretion and excretion have been determined, together with mass of zinc in tissues and in the whole body. The model has been used to identify five sites of long-term regulation of zinc metabolism in humans. These sites are absorption, excretion, exchange with red blood cells, release of zinc from muscle and secretion of zinc into gut. The model is currently being applied to several areas of nutrition including the effects of dietary fiber on zinc stores, the effects of aging on zinc metabolism and the zinc requirements of neonates.

By first using some simple linear curve fitting method, (such as spline fitting), on data following a compartmental model, direct application of linear regression can then be made to the system of differential equations describing this data. This allows information about the parameters governing the system to be obtained from tracer and tracee measurements. It simplifies both the process of determining which parameters are estimable from various measurements, as well as the estimation process itself. Since it does not rely on knowledge of a simple closed form of the solution it has the potential to make full use of data measured over very long time periods under nonequilibrium conditions. Essentially it allows introduction of sequential estimation methods of statistics. These results can then be used to predict future substrate concentration from known substrate production, or determine substrate production from concentration measurements. A byproduct of these methods is the ability to estimate parameters in data assumed to be a finite linear combination of exponentials or sinusoids of unknown exponents or frequencies, without use of complicated nonlinear regression methods.

Several major physiological changes or disease states occur more frequently in alcohol abusers or prolonged high users. These include: cancer, immunosuppression, and nutritional deficiencies. They interact with potential enhancement of cancer growth or survival. Clearly alcohol abuse yielding cirrhosis is associated with immunosuppression of cellular immune functions. Severe, prolonged ethanol consumption frequently is associated with one or more nutrient deficiency. Such deficiencies are more common when there are other major problems such as liver or pancreas damage and in prolonged alcohol abusers should influence the host defenses against pathogens and tumors. The amount and frequency of nutritional and immunological deficiencies with "binge" or less severe alcohol abuse is less clear, but animal studies suggest they are frequently present. Clearly, nutrient deficiencies are common in alcohol abusers and could play significant roles in ethanol associated problems including immunosuppression. Data summarized suggest that immunosuppression caused by nutritional deficiencies and/or direct effects of ethanol and its' metabolites on lymphoid cells is a potential component of cancer in alcohol abusers. However the frequent occurrence of nutritional deficiencies, immunosuppression, and certain cancers in severe, prolonged ethanol abusers is an association, not proven cause and effect.

Fundamentals of modeling of in vivo nutritional and metabolic systems are discussed. Emphasis is placed upon the potential usefulness of models, and the relationship between utility and model complexity. With the glucose regulating system used as a metaphoric example, the balance between available data and model simplification is drawn, with the goal of obtaining a representation of optimal complexity. From such an optimization procedure, it is argued that the maximum usefulness of models can be obtained with respect to the testing of specific physiological hypotheses, and the estimation of unmeasurable parameters or variables. The view is expressed that only with careful modeling procedures, in which principles of optimal complexity are applied, will the impact of models of nutritional systems be significant.

The shape of the labelling curve for urinary pyridoxic acid following a single dose of labelled pyridoxine can be most easily described by a two compartment model. However, the usefulness of such a model is limited because the two pools have no physiological identity; the model does not describe the many metabolic interconversions associated with vitamin B6 metabolism; and the predictions of the total size of the vitamin B6 pool are not consistent with data from direct measurements. Therefore, we have been using the Simulation, Analysis, and Modelling program (SAAM) developed at the National Cancer Institute to develop an improved model. Since the SAAM 29 program is limited to 25 pools, only a few of the many tissue vitamin B6 pools could be included. Muscle and liver were chosen because they contain 80 to 90% of the vitamin B6 in the body. Plasma and erythrocytes were selected because of their importance in transport. This review traces the development of the model to its current stage and shows comparisons between the predictions of the model and a variety of data from the literature. At this point the emphasis has been on describing metabolism in rats because the most detailed kinetic data available were obtained from rats. The predictions of the current model do not match all available observations. However, the results are sufficiently encouraging to warrant continued development.

Saturation kinetics experiments, in which uptake U of a substance across a transport barrier is measured as a function of initial concentration difference C, are used to describe transport of nutrients. Many such processes are characterized by low- and high-affinity systems in which kinetic parameters Vmax and Km differ by orders of magnitude. Transformations of equations to straight-line relationships between U and C are popular methods of parameter estimation. The aims of this study are (1) to show effects of random errors in U measurement on Vmax and Km estimation in a two-affinity process under several transformations: Lineweaver-Burk (1/U vs. 1/C), Hanes (C/U vs. C), Eadie-Hofstee (U/C vs. U), and Wolff (U vs. U/C), and (2) to indicate strategies for minimizing effects of errors. Two transport properties will illustrate: an ideal process of low- (Vmax = 100, Km = 10) and high-affinity (Vmax = 1, Km = .1) systems to which random error is added, and experimental uptake of 5-methyltetrahydrofolic acid by isolated hepatocytes.

The effect of zinc nutriture and metabolism on brain function has been reviewed. Zinc nutriture and its effect on the concentration and metabolism of essential elements (e.g. zinc, copper, manganese, magnesium, sodium, potassium and calcium) and on the concentration and metabolism of toxic elements (e.g. aluminum and lead) are discussed in relationship to brain function. In addition, possible interrelationships between zinc nutriture and metabolism and its effect on a number of diseases including acrodermatitis enteropathica, Pick's disease, Alzheimer's disease, schizophrenia, fifth day fits, and epilepsy are discussed. Descriptions and comparisons of methods to measure brain zinc are presented. Behavioral changes and the altered brain morphology which have been associated with zinc deficiency are reviewed. Some possible mechanisms for the association of anorexia with zinc deficiency are outlined. Perinatal brain damage produced by early zinc deficiency followed by rehabilitation with adequate zinc appears to be long term, maybe permanent. Interrelationships between zinc nutriture and aspects of neurochemistry are outlined. Some of the neurochemistries discussed include nucleic acid and protein synthesis, cytoskeletal proteins, neurotransmitters (e.g. catecholamines, indoleamines, glutamate, gamma-aminobutyric acid, and neuropeptides), neurotransmitter receptors, 7S nerve growth factor and zinc-binding proteins. Recent evidence linking zinc and neurotransmission is discussed.