Progress in food & nutrition science最新文献

Studies done on dietary fiber (DF) over the past five years are presented in this Review. The involvement of dietary fiber in the control of plasma glucose and lipid levels is now established. Two dietary fiber sources (soybean and fenugreek) were studied in our laboratory and are discussed herein. These sources were found to be potentially beneficial in the reduction of plasma glucose in non-insulin dependent diabetes mellitus subjects. They are shown to be acceptable by human subjects and are easy to use either in a mixture of milk products and in cooking. The mechanism by which dietary fiber alters the nutrient absorption is also discussed. The effect of DF on gastric emptying, transit time, adsorption and glucose transport may contribute to reducing plasma glucose and lipid levels. DF was found to be effective in controlling blood glucose and lipid levels of pregnant diabetic women. Dietary fiber may also be potentially beneficial in the reduction of exogenous insulin requirements in these subjects. However, increased consumption of DF may cause adverse side effects; the binding capabilities of fiber may affect nutrient availability, particularly that of minerals and prolonged and high DF dosage supplementation must be regarded cautiously. This is particularly true when recommending such a diet for pregnant or lactating women, children or subjects with nutritional disorders. Physiological effects of DF appear to depend heavily on the source and composition of fiber. Using a combination of DF from a variety of sources may reduce the actual mass of fiber required to obtain the desired metabolic effects and will result in a more palatable diet. Previously observed problems, such as excess flatus, diarrhea and mineral malabsorption would also be minimized.

Human civilization and a concomitant increase in industrial activity has gradually redistributed many toxic metals from the earth's crust to the environment and increased the possibility of human exposure. Among the various toxic elements, heavy metals cadmium, lead, and mercury are specially prevalent in nature due to their high industrial use. These metals serve no biological function and their presence in tissues reflects contact of the organism with its environment. They are cumulative poison, and are toxic even at low dose. Studies of metabolism and toxicity of these elements have revealed important interactions between them and some essential dietary elements like calcium, zinc, iron, selenium, copper, chromium, and manganese. In general, a deficiency of these essential elements increases toxicity of heavy metals, whereas an excess appears to be protective. While most of the observations are on laboratory animals, limited human data are in agreement with the results of animal experiments. These suggest that the dietary presence of the essential elements may contribute to the protection of man and animal from the effects of heavy metal exposure, while their deficiency may increase toxicity. Appropriate dietary manipulation thus may be valuable in the prevention and treatment of heavy metal toxicity.

This review deals with compounds -mainly organic-which when present in the diet, may affect the health of livestock or interfere with normal feed utilization. The anti-nutrients occur as natural constituents of plants and animal feeds, as artificial factors added during processing, or as contaminants of the ecosystem. Their mode of action, metabolism in the living body, and detoxification mechanisms, are described briefly. It is stressed that ruminants and monogastric species frequently differ in susceptibility to the same toxicant, mainly due to the action of rumen microorganisms. The toxicants described are classified as follows: proteins depressing digestion (protease inhibitors and lectins); glucosides; phenolic substances; other toxicants occurring in plants; substances interfering with the utilization of vitamins; mycotoxins; pesticides and industrial chemicals.

Several domesticated species of mammals are raised to provide protein for human consumption. The goal of producers is to generate a product, lean meat, efficiently. Much of the weight gain of animals is fat, a large portion of which is not needed by the animal and unwanted by the human consumer. Thus, improvement in efficiency of animal growth must consider not only rate of weight gain and use of feed to support the gain but also the composition of the gain. One method to improve efficiency of growth, including body composition is to lower the energy intake of animals; feeding less than ad libitum is particularly effective for some species. There are three types of endocrines, anabolic steroids, growth hormone and adrenergic agonists, that have demonstrated ability to change mammalian growth and body composition. Exogenous anabolic steroids increase weight gain, improve efficiency of feed utilization and change body composition toward more muscle and less fat. They are especially effective in ruminant species and are used in beef cattle. Exogenous growth hormone has the same effects as anabolic steroids but is effective in nonruminant species as well. Exogenous adrenergic agonists, analogs of norepinephrine, have marginal effects on weight gain and feed efficiency but favorably change body composition in all species. As more is understood about the control of endocrine secretion, the possibility arises for animal manipulation by administration of exogenous releasing factors or release-inhibiting factors or by changing central nervous system neurotransmitter control of the hypothalamic production and release of these factors. It is also possible to use selective immunization to modify endogenous hormones. Thus, biological knowledge coupled with modern technology continues to open many frontiers to favorably change animal growth and composition. Some of these approaches are in use, several are in experimental use and others await experimental demonstration of utility.

Proteins associated with metals serve many important biological functions. The amino acid residues provide the functional groups in a protein which are the potential ligands for a metallic cation. Metals impart various effects on protein structure and bring about overall structural stability. These effects are seen in quarternary, secondary and tertiary structures of the protein. There are varieties of approaches to study metal protein interactions. The earliest technique being the equilibrium dialysis which is still used extensibly to determine the binding strength and the number of metals bound per protein molecule. There are a number of other techniques available which provide precise information about the nature of metal binding sites. They include electron spin resonance, UV and visible spectoscopy, nuclear magnetic resonance, resonance Raman, X-ray crystallography, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (XAFS), etc. Selected metal protein interactions are discussed in this review. Albumin is the major plasma protein in blood which transports a number of metals. Detailed studies of Cu(II) and Ni(II) binding to albumin suggests that both metals have the same specific binding site at the NH2-terminal tripeptide sequence (Asp1-Ala2-His3...) involving the Asp alpha-NH2, His3 N (1) imidazole, two deprotonated peptide nitrogens (Ala2NH and His3NH), and Asp1 COO- group. Transferrin transports Fe(III) in blood. The protein possesses two metal-binding sites, each within a domain of bilobal proteins. Presence of carbonate is an important feature of Fe(III)-binding to transferrin. The binding site has been postulated as one involving Tyr 185 and Tyr 188 and suggests that two of the three histidines His 119, His 207 and His 249 also serve as ligands. Arginine 145 is a likely anchor for the carbonate anion. Superoxide dismutase is an enzyme found in erythrocytes which catalyzes the dismutation of superoxide radical. The protein is a dimer made up of two equivalent subunits. The subunits are held together by noncovalent interactions. For optimal enzymatic activity, at least two of the protein's four metal ions must be cupric. The results of the X-ray crystal structural analysis for Cu(II) and Zn(II) containing protein have been reported. In the metal-binding region of one subunit, Cu(II) and Zn(II) are separated by approximately 6A. The Cu(II) is bound to imidazole side chains of histidines 44, 46, 61 and 118 in a distorted square planar arrangement. The imidazole ring of histidine 61 is believed to be deprotonated and to serve as a bridge between Cu(II) and Zn(II).(ABSTRACT TRUNCATED AT 400 WORDS)

Cultural nutrition encompasses a wide sweep of food-related themes within three major categories: arts and humanities, social sciences, and biological-natural sciences. The paper, first of three, considers the arts and humanities. Topics include food and diet expressed through art, film, music, and dance. The essay then examines food and diet in representative works of literature, both ancient and modern. The place of food and diet within folklore, mythology, and religion is treated, with consideration of symbolic roles played by food throughout the human life cycle, especially with birth and infancy, coming-of-age, marriage, and death. Religion, a major theme in cultural nutrition, is explored and the food-dietary patterns of Jews, Christians, Moslems, Hindus, and Shintos are treated. Ethics and philosophy are examined as both relate to programs of international food relief and vegetarianism. The essay concludes with a review of work by historians, especially themes of famine and approaches taken to refeed populations during combat and hostilities.

Vitamin A, an unsaturated 20 carbon cyclic alcohol, has a variety of physiological functions including a role in vision, reproduction, growth and maintenance of epithelial and bone structures. The main sources of vitamin A are from preformed vitamin A in animal foods or from -carotene in green plants. Carotene is cleaved in the intestinal mucosa to retinol, which is transported in chylomicrons mainly to the liver which is the major storage site of vitamin A, where stores are mainly of retinyl palmitate. Utilization of vitamin A appears to be a highly regulated process; retinol is transported in the serum bound to a specific binding protein. There also may be some control of the level of retinol in cells possibly through membrane receptors or of excretion from the cell. Intracellular cytosolic retinol binding proteins transport retinol to the nucleus where specific receptors for retinol have been found. Intracellular binding proteins for retinoic acid and retinal, metabolites of retinol have also been found, and an interstitial protein transporting retinol is present in the eye. Vitamin A deficiency causes cessation of growth, night blindness, and renders the organism more susceptible to infection, and vitamin A supplementation has been shown to enhance immune response. Epidemiological studies have shown low vitamin A and carotene to be correlated with incidence of cancer. Excess vitamin A intake results in hypervitaminosis with severe detrimental effects. Vitamin A requirements appear to be met in most developed countries although in the populations at greatest risk, newborns and pregnant and nursing women, cases of deficiency are observed. However, in large areas of the world vitamin A deficiency is endemic, causing widespread blindness and mortality.

Given the heightened interest in nutritional aspects of exercise, and an increase in athletic participation by women, it appeared timely to review the nutritional implications of exercise in women. The initial part of this paper contains a compilation of published studies on the nutrient intakes of female athletes. These reveal that most groups of athletes have adequate nutrient intakes, and that their vitamin and mineral intakes appear to be superior to those of nonathletic women. The average energy intake of athletes in studies summarized in this paper was 2069 kcal, and for certain groups of athletes, energy intakes were even lower. How these women manage to train intensely while consuming energy intakes similar to those of sedentary women is not readily apparent, and for this reason, the remainder of the paper discusses energy balance as affected by activity. Methodological considerations related to assessment of the components of the energy balance equation (food intake, energy expenditure, and body energy stores) are presented, with a focus on considerations in women. The effects of activity on each of these components are then discussed in an attempt to determine whether some form of energy conservation may occur. Finally, effects of activity on the menstrual cycle are reviewed. The observed changes are discussed in relation to nutrition 1) in terms of how nutrition may play a role in their causation; and 2) in terms of their nutritional implications for the amenorrheic athlete, specifically as regards energy balance and bone density.

Metallothionein is an important metal-binding protein which occurs in varying amounts in a wide range of tissues but particularly in liver, kidneys, intestine and pancreas. Synthesis of the protein is induced by zinc and copper and also by cadmium and many other non-essential elements. The concentration of the protein in tissues depend on zinc and copper status and on patho-physiological state. A variety of stress factors stimulate metallothionein synthesis, particularly in liver. The turnover rate of metallothionein in tissues is relatively high but depends to a large extent on its metal content. There has been much speculation as to the function of the protein and one important role appears to lie in the cellular detoxification of copper, zinc and other metals. Metallothionein also appears to participate in metabolic interactions between zinc and copper. The protein occurs in small amounts in blood and urine and assay of these concentrations may be used in the assessment of trace element status.