Dietary Constituents

Due to the potency of the redox system of vitamin C s two forms, several further interactions with readily oxidizable nutrients exist. The redox system is able to protect sulfhydryl groups of proteins as well as polyunsaturated fatty acids from oxidation. The close relationship of the nutritive antioxidants vitamin C, vitamin E, and P-carotene can be seen not only in cellular antioxidative metabolism but also during absorption. In the presence of ascorbic acid the absorption of these antioxidants is improved due to the protecting characteristics of vitamin C. 

Interactions of ascorbic acid with folic acid have also been observed. Studies with guinea pigs have shown that folic acid deficiency is related to decreased concentrations of ascorbic acid in liver and adrenals (Lewis et ai, 1982). 

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Any substance that destroys, inactivates, or in other ways renders unavailable an essential dietary constituent can be termed an antinutrient. The most... 

At various times, antivitamin factors specific to vitamin folic acid, and choline have been reported. However, it is uncertain whether these are tme antimetaboHtes or if they may result from metaboHc interrelationships with other dietary constituents. 

A wide variety of animal species are subjected to the administration of drugs during their lifetime.The various animal species can encounter drugs and other dietary additives by different routes and this is dependent on the environment in which they are kept. Intensively reared animals tend to have considerable consistency in the components of their diets and thus are much less likely to encounter the range of naturally produced compounds that extensively produced animals encounter. The desire for less expensive dietary constituents and increased efficiency of use has induced feed manufacturers and producers to add enzyme supplements to diets of most farmed animals to reduce the negative effects of indigestible dietary carbohydrates, refactory proteins and unavailable minerals such as phosphorus. This use of dietary additives to improve nutrient utilization and environmental consequences of feeding animals intensively has been the subject of intense research activity in the last five years. " The... 

SEERAM N P and NAIR M G (2002) Inhibition of lipid peroxidation and structure-activity-related studies of the dietary constituents autocyanins, autocyanidins, and catechins, JAgric Food Chem, 50, 5308-12. 

Of dietary constituents studied, only caffeine negatively impacted calcium and bone metabolism. 

Blake KCH, Barbezat GO, Mann M. 1983. Effect of dietary constituents on the gastrointestinal absorption of 203Pb in man. Environ Res 30 182-187. 

With such a large surface area available for the absorption of nutrients, there is the potential for the absorption of dietary constituents that could be harmful to the health of an individual. Thus, in order to protect against dietary toxins, there are a series of barriers, which must be overcome before a molecule can enter the systemic circulation. This applies equally to drug molecules. 

The expression of a significant gut wall first-pass extraction ratio has several implications for affected drugs. First, oral bioavailability is lower than would be expected from the extent of absorption and the hepatic first-pass extraction. Second, the variability in expression of gut wall metabolic enzymes and transporters can lead to significant variability in gut wall first-pass extraction and thus oral bioavailability. Finally, the site of expression of these enzymes and transporters (i.e., the villus tip) brings them into contact with potentially co-administered drugs or dietary constituents, which could be inhibitors or inducers. Thus, there is the potential for drug-drug interactions at the level of the gut wall. 

Wattenberg LW. 1975. Effects of dietary constituents on the metabolism of chemical carcinogens. Cancer Res 35(11) 3326—3331. 

Since in mammalian species metals first need to be assimilated from dietary sources in the intestinal tract and subsequently transported to the cells of the different organs of the body through the bloodstream, we will restrict ourselves in this section to the transport of metal ions across the enterocytes of the upper part of the small intestine (essentially the duodenum), where essentially all of the uptake of dietary constituents, whether they be metal ions, carbohydrates, fats, amino acids, vitamins, etc., takes place. We will then briefly review the mechanisms by which metal ions are transported across the plasma membrane of mammalian cells and enter the cytoplasm, as we did for bacteria, fungi and plants. The specific molecules involved in extracellular metal ion transport in the circulation will be dealt with in Chapter 8. 

The experiments described in this chapter show how three fairly simple approaches—respiratory studies, balance measurements, and observations on growth—were applied to animals including man, so that by 1930-1940 energy requirements and the major and essential minor dietary constituents were known. In a few instances of dietary... 

In the event of dietary Ca abundance, Ca in excess of adequate circulating concentrations is deposited in the skeleton. This occurs to the extent of the body s ability to store Ca, and any excess beyond this threshold is excreted. Accrual of Ca into bone is governed by such factors as dietary intake (including the absorption, bioavailability, utilization of nutrients and minerals, and other dietary constituents that influence absorption or retention), calciotropic hormones, genetic potential, lifestyle factors, life stage, general health, and the adaptive response to physical/mechanical stimuli within the constraints of metabolic economy. 

We have already met several of the important concepts in this topic, so now it is time to round them up and bring out the major principles. In the first place drug molecules clearly might interact with food molecules in the lumen of the gut. Perhaps the best-known example of this is the interaction between the tetracyclines and dietary calcium and iron. The binding, which occurs between them, produces a chelate, which is not particularly lipid-soluble, and therefore the overall absorption of tetracycline may be reduced to the point where plasma levels do not achieve effective antibiotic concentrations. The commonest dietary constituent to produce this binding is milk with its high calcium content. Tetracycline ingestion should be separated from food as far as possible. 

Solomons NW, Viteri F, Shuler TR, et al. 1982. Bioavailability of nickel in man Effects of food and chemically defined dietary constituents on the absorption of inorganic nickel. J Nutr 112 39-50. 

Urgert, R., M. P. M. E. W. Van Der Wouw, R. Hovenier, P. G. Lund-Larsen, and M. B. Katan. Chronic consumers of boiled coffee have elevated serum levels of lipoprotein (A). J Intern Med 1996 240(6) 367-371. Abraham, S. K. Anti-genotoxic effects in mice after the interaction between coffee and dietary constituents. Food Chem Toxicol 1996 3(1) 15-20. Urgert, R., M. P. M. E. Weusten-Van Der Wouw, R. Hovenier, S. Meyboom,... 

CA191 Abraham, S. K. Anti-enotoxic effects CA203 in mice after the interaction between coffee and dietary constituents. Food Chem Toxicol 1996 34(1) 15-20. 

Wattenberg, L.W., Inhibition of carcinogenesis by minor dietary constituents, Cancer Res., 52, 2085, 1992. 

Leucine, an essential dietary constituent for human beings, is synthesized in many bacteria and plants using pyruvate as a starting material. Outline this pathway of metabolism and illustrate the chemical reaction mechanisms involved in each step. 

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