The absorption of minerals

Most minerals are absorbed by carrier-mediated diffusion into intestinal mucosal cells and accumulated by binding to intracellular proteins. There is then sodium-dependent active transport from the epithelial cells into the bloodstream, where again they are usually bound to transport proteins. Genetic defects of the intracellular binding proteins or the active transport systems at the basal membrane of the mucosal cell can result in functional deficiency despite an apparently adequate intake of the mineral. 

The absorption of many minerals is affected by other compounds present in the intestinal lumen. As discussed in section 4.5.1, a number of reducing compounds can enhance the absorption of iron, and a number of chelating compounds enhance the absorption of other minerals. For example, zinc absorption is dependent on the secretion by the pancreas of a zinc-binding hgand (tentatively identified as the tryptophan metabolite picolinic acid). Failure to synthesize and secrete this zinc-binding ligand as a result of a genetic disease leads to the condition of acrodermatitis enteropathica— functional zinc deficiency despite an apparently adequate intake. 

Diets based on unleavened wheat bread contain a relatively large amount of phytic acid (inositol hexaphosphate), which can bind calcium, iron and zinc to form insoluble complexes that are not absorbed. Phytases in yeast catalyse dephosphorylation of phytate to products that do not chelate the minerals. 

Polyphenols (section 7.5.2.3), and especially tannic acid in tea, can also chelate iron and other minerals, reducing their absorption, and large amounts of free fatty acids in the gut lumen (associated with defects of fat absorption section 4.3.2) can impair the absorption of calcium and magnesium, forming insoluble soaps. 

Only about 10% of dietary iron is absorbed, and only as little as 1-5% of that in many plant foods. As discussed in section 11.15.2.3, iron deficiency is a serious problem some 10-15 % of women of child-bearing age have menstrual iron losses greater than 

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Although many physiological and biochemical processes In plants are affected by various allelochemicals, In most Instances the details of the mechanism of action of a particular allelochemical have not been elucidated. Because soil mediates the transfer of most allelochemicals (except perhaps volatile compounds) from a donor to a receiver, plant roots are often the first tissues to contact an allelochemical. Thus, It Is not surprising that root growth and development are Inhibited In many Instances of allelopathy (1.-3) One of the primary physiological functions of plant roots Is the absorption of mineral nutrients. Therefore, It Is logical that the Influence of allelopathic Interactions on mineral absorption by plant roots has been Investigated. 

Dietary Reference Intake (DRI) of Cu, 17-18% of the DRI of K, P, and Fe, and between 5 and 13% of the DRI of Zn, Mg, and Mn (Table 5.1). Potatoes are generally not rich in Ca, but can be a valuable source of trace elements, such as Se and I, if fertilized appropriately (Eurola et al., 1989 Poggi et al., 2000 Turakainen et al., 2004 Broadley et al., 2006). Moreover, since potato tubers have relatively high concentrations of organic compounds that stimulate the absorption of mineral micronutrients by humans, such as ascorbate (vitamin C), protein cysteine and various organic and amino acids (USDA, 2006), and low concentrations of compounds that limit their absorption, such as phytate (0.11-0.27% dry matter Frossard et al., 2000 Phillippy et al., 2004) and oxalate (0.03% dry matter Bushway et al., 1984), the bioavailability of mineral elements in potatoes is potentially high. 

Prebiotics and synbiotics containing fructooligosaccharides enhance mineral bioavailability by improving the absorption of minerals in the colon, especially calcium, iron, and magnesium (Caers, 2004 Coudray, 2004 Hidaka et al., 2001 Ohta et al., 1994 Roberfroid, 2005). The mechanism... 

The behavior of minerals is often influenced by the presence of other food constituents. The recent interest in the beneficial effect of dietary fiber has led to studies of the role fiber plays in the absorption of minerals. It has been shown (Toma and Curtis 1986) that mineral absorption is decreased by fiber. A study of the behavior of iron, zinc, and calcium showed that interactions occur with phytate, which is present in fiber. Phytates can form insoluble complexes with iron and zinc and may interfere with the... 

In discussing the absorption of minerals, especially In the context of their biological availability. It Is Important to clarify three terms for the subdivisions of the absorptive process uptake refers to the entrance of the nutrient Into the mucosal cell from the intestinal lumen transfer refers to the passage of the nutrient out of the mucosal cell and transport refers to the removal of the nutrient from the vicinity of the Intestine to other parts of the organism. All three processes are essential for a dietary component, such as zinc, to achieve a nutritional role for the the organism. From the array of mechanisms thought... 

Saturated fatty acids are better absorbed as MAGs than as FFA, as the latter can form less-absorbable hydrated acid soaps and complexes with calcium and other divalent ions (41). The effect is more pronounced when the amount of calcium in the diet is high (42). In the presence of insoluble soaps, cholesterol absorption may be reduced (43). Thus, the stereospecific position of fatty acids in the TAGs can have an effect on their absorption and on the absorption of minerals and other lipid constituents. 

Hypha (plural, hyphae)—Cellular unit of a fungus, typically a branched and tubular filament. Many strands (hyphae) together are called mycelium. Root hair—These are tiny, tubular outgrowths of the root epidermis, mostly occurring behind the actively growing root tip, and used to increase surface area of the root to enhance the absorption of minerals and water from the soil. 

Nowadays saponins have been studied because different beneficial properties to health have been described. Saponins possess a broad variety of biological effects analgesic, antiinflammatory, antimicrobial, antioxidant, antiviral, and cytotoxic activity, effect on the absorption of minerals and vitamins and on animal growth, hemolytic and immunosti-mulatory effects, increased permeability of the intestinal mucosa neuro-protective action, and reduction of fat absorption (Gu lii-Ustundag and Mazza, 2007). However, the biological properties of quinoa saponins require further study. 

In 1923, Hevesy applied his radioactive tracer studies to the absorption of minerals by plants. It had long been assumed that plants, in contrast to animals, do not excrete the minerals they absorb. Hevesy demonstrated that solutions containing the lead isotope then termed thorium-B were absorbed by plants and caused them to retain some radioactivity. When unlabelled lead solution was subsequently used as nutrient, Hevesy found that the radioactive isotope gradually returned to the nutrient solution. Clearly, there was active metal exchange occurring at all times. 

Organic acids may improve the absorption of minerals, such as Ca, P, Mg and Zn, in the small intestine (Kirchgessner and Roth, 1988). The presence of anions appears to facilitate cation mineral absorption, and formic, fumaric and n-butyric acid have all been shown to improve apparent total tract digestibility of Ca and total P, as well... 

The refining of cereals leads to an appreciable fall in their mineral content but, on the other hand, dietary fibre decreases the absorption of minerals such as calcium and iron. It has been suggested that in Britain the consumption of wholemeal chapattis may be a factor in causing rickets and osteomalacia in immigrants from the Indian subcontinent. These subjects tend to be deficient in vitamin D (page 156) and therefore to absorb and metabolize the available calcium less efficiently. 

Currently, it is not possible to recommend a specific intake of fiber more research is needed. However, dramatic increases in dietary fiber should be avoided since the absorption of minerals may be reduced by high dietary fiber intakes. Moderate increases in the consumption of fiber can be easily achieved by increasing the consumption of nuts, vegetables, fruits, and whole grain cereal products. The fiber content of various foods is given in Food Composition Table F-21. 

Fiber—Plant foods that contain large amounts of indigestible carbohydrate (fiber) tend to stimulate more rapid movements of the intestine, so that the absorption of minerals and other nutrients may be reduced. Another way in which fiber may reduce mineral absorption is by enveloping certain mineral elements so that they pass into the stool with the indigestible matter. 

Medium-chain fatty acids also improve the absorption of many other nutrients. The absorption of minerals (particularly calcium and magnesium), B vitamins, fat soluble vitamins (A, D, E, K and beta-carotene) and also amino acids has been foimd to increase when infants are fed a diet containing MCFA. In addition, coconut oil can be digested by the salivary lipase, getting absorbed very fast to give energy like carbohydrates. All other fats need the pancreatic lipase for digestion that the infants do not have (Murthi et al., 1987). 

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