Lead-phytate

By virtue of rendering iron catalytically inactive, dietary phytate may also suppress the incidence of colonic cancer (J2j>). Intestinal aerobic bacteria and/or minor inflammatory events generate substantial amounts of O27 leading to OH formation and lipid peroxidation. These two processes are thought to be important elements in tissue injury which occurs during inflammation. This argument is compatible with the observation that colonic cancer is frequently preceded, or accompanied, by pigmentation of the colonic epithelium lipofuscin, a byproduct of lipid... 

Gastrointestinal absorption, and subsequent utilization and retention by the body, of essential trace elements such as zinc, copper, and selenium can also be enhanced or diminished by the presence or absence of other trace elements and chemicals in the diet (WHO, 1996). For example, cadmium and lead absorption is enhanced when dietetic intake of calcium, iron, and phosphate is low. Phytate, an organic phosphate that is abundant in diets high in unrefined grains, especially when accompanied by high dietetic calcium, helps suppress the uptake of potentially toxic elements such as lead and cadmium, but also inhibits the uptake of essential zinc (WHO, 1996). 

The National Cancer Institute, through its Experimental Food Program (3), has identified many phytochemicals that can interfere with and potentially block the biochemical pathways that lead to malignancy in animals. These phytochemicals fall into approximately 14 classes of substances that are present in common foods. They include sulfides, phytates, flavonoids, glucarates, carotenoids, coumarins, monoterpenes, triterpenes, lignans, phenolic acids, indoles, isothiocyanates, and polyacetylenes. 

The utilization of the macro element calcium is impaired by a high intake of lead, magnesium, aluminum and phytate, that of magnesium by lead, calcium, nickel, and phytate, and that of phosphorus by magnesium, calcium, and phytate. Several experiments in animals have strikingly illustrated the importance of a trace element dietary balance in determining the safe intake of a particular macro, trace or ultratrace element (O Dell 1997, Griin et al. 

There are numerous reports of interactions of dietary elements that cause variation in the absorption of chromium. Amino acids, which chelate chromium, prevent precipitation at the basic pH in the small intestine, which increases its absorption [13]. Other chelating agents have mixed effects. Phytates significantly decrease absorption whereas oxalates lead to increased absorption [15]. Certain vitamins such as nicotinic acid and ascorbic acid have been shown to increase absorption [16]. Starch has also been shown to increase absorption to a greater degree than glucose, fructose, and sucrose. Some metals can compete with chromium and decrease its absorption. Studies show that zinc, vanadium, and iron have a common intestinal transport mechanism with chromium and can decrease the absorption of chromium [9]. 

The bioavailability of zinc depends on different factors that inhibit or facilitate it. Cereals, for instance, are rich in zinc, but the absorption is poor due to the phytate ligands that are also present [9]. Similarly, the technologies used in food refining, preparing, and cooking may lead at one time to an increase of zinc (zinc-coated packing or household utensils) and at another time to a decrease of zinc [5]. 

Calcium forms stable insoluble salt with oxalic acid (see Section 10.2.3.2). In plant cells with higher concentrations of oxalic add, caldum oxalate can be actually present in the form of crystals. Some plants have been shown to bind metals in mixed complexes. For example, chromium can be bound in an oxalate-malate complex, and nickel and zinc can form a dtrate malate complex. Citric add has been proven to be a low molecular weight zinc ligand in human milk, and in casein micelles it binds calcium. It is also used as a food additive (acidulant, synergist to antioxidants and sequestrant), so great attention has been paid to the formation of its complexes with metal ions. The addition to cereal products leads to increased solubihty of naturally present iron, due to its release from phytic acid salts (phytates). 

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