Bioavailability from food source

The issue of bioavailability from food sources and the interactions between food groups and copper availability remains a critical question. Lonnerdal et al. demonstrated that heat treatment of cows milk formula decreases the copper bioavailability. Transitional complexes form in the milk upon heating that have a similar configuration to copper and thereby directly inhibit copper absorption. High doses of zinc also reduce copper bioavailability, as does combined iron and zinc supplementation. The dilemma is how to prepare an infant formula containing adequate copper, iron, and zinc that will meet the RDA for copper. Other nutrients dramatically affect copper absorption from foods. Soy protein-based diets promote less copper retention in tissues than lactalbumin-based diets. However, it is unclear if this effect is solely due to the soy protein composition or to the higher zinc in these soy-based formulas. In animals, phytate causes a drop in serum copper but human stable isotope studies reveal no... 

While effective doses of 1 to 2 mg seem small, the total body pool of /3C can be estimated at 15 to 20 mg, with a total plasma pool of ateut 0.5 to 1 mg. In comparison with these pool sizes, a 2-mg effective dose is relatively large. In addition, the average daily effective dose of jSC from food sources is likely to be less than 1 mg, since matrix effects probably impair bioavailability of /3C to a larger extent than with supplements such as that used by van Vliet et al (1995). The minimum effective dose required to yield a significant TGR fraction response, taking into account the error associated with measurement, has not been determined, but is not likely to be much less than 1 mg. Consequently, use of unlabeled jSC, even coupled with use of the TGR fraction, is probably not well suited to study /3C uptake and metabolism at effective doses typically derived from dietary sources. 

Plants contain to some extent less bioavailable forms of vitamin B6, e.g., glycosylates, or biologically inactive metabolites, e.g., e-pyridoxin-lysin-complexes. In addition, the release of vitamin B6 from foods rich in fiber is assumed to be delayed. The bioavailability of vitamin B6 from animal-derived foods is therefore overall higher than from plant-derived foods. Good dietary sources of vitamin B6 include chicken, fish, pork, beans, and pulses [1]. 

In the total plasma response approach, the bioavailability of a compound is determined by measuring its plasma concentration at different times (up to weeks) after single or long-term ingestion of the compound from supplements or food sources. Generally, a plasma concentration-versus-time plot is generated, from which is determined the area-under-curve (AUC) value used as an indicator of the absorption of the componnd. Here, the term relative bioavailability is more appropriate since AUC valnes of two or more treatments are usually compared. This is in contrast to absolnte bioavailability for which the AUC value of the orally administered componnd is compared to that obtained with intravenous administration taken as a reference (100% absorption). 

In addition to its broad occurrence under contrasting conditions, easy collection, relatively long life span, and resistance to the accumulation of toxic chemicals, zebra mussels provide a link between the pelagic and benthic food webs, possibly creating a rapid pathway for contaminant transfer from sediments to predators such as common carp (Cyprinus carpio) and, occasionally, humans [32, 42—4-7]. Consequently, zebra mussel has been considered a potential sentinel organism for assessing Hg redistribution from point sources in the Ebro River and the degree of bioavailability to river and wetland food webs. 

The bioavailability of selenium to a benthic deposit-feeding bivalve, Macoma balthica from particulate and dissolved phases was determined from AE data. The selenium concentration in the animals collected from San Francisco Bay was very close to that predicted by a model based on the laboratory AE studies of radiolabelled selenium from both particulate and solute sources. Uptake was found to be largely derived from particulate material [93]. The selenium occurs as selenite in the dissolved phase, and is taken up linearly with concentration. However, the particle-associated selenium as organoselenium and even elemental selenium is accumulated at much higher levels. The efficiency of uptake from the sediment of particulate radiolabelled selenium was 22%. This contrasts with an absorption efficiency of ca. 86% of organoselenium when this was fed as diatoms - the major food source of the clam. The experiments demonstrated the importance of particles in the uptake of pollutants and their transfer through the food web to molluscs, but the mode of assimilation was not discussed. 

The bioavailability of calcium from dairy foods is considered to be excellent (Schaafsma 1983). Evidence from animal studies suggests that the form of calcium in dairy foods may influence the bioavailability of this mineral (Wong and LaCroix 1980). For example, dairy foods that contain colloidal calcium phosphate or calcium caseinate (e.g., as in Cheddar cheese) appear to be somewhat better sources of calcium than foods that contain ionic calcium (e.g., yogurt, buttermilk). However, calcium in milk and other milk products is of greater bioavailability to humans than calcium found in other food sources. According to Renner (1983), calcium utilization from skim milk powder is 85% compared with 22-74% from vegetables. Dietary fiber in plant cell... 

All these studies suggest that the metabolic pathway is the same for free and bound forms of ferulic acid. Whereas the free form is rapidly absorbed, metabolized and excreted in urine, the bound form allows a longer time period (free and conjugated) in plasma, as already suggested by the absence of free ferulic acid in rat plasma 18 h after intake from an enriched diet, whereas its metabolites were still present [Adam et al., 2002]. Even though its bioavailability, in terms of half-life in plasma and low excretion in urine, was improved when esterified, the absorption of ferulic acid from a wheat source was lower than if present as free form in a diet [Rondini et al., 2004]. This indicates that the amounts of ferulic acid circulating in plasma as well as its circulating metabolites are dependent on its form present in the food source. 

Bioavailability from Environmental Media. Chlorobenzene is absorbed primarily following inhalation of contaminated air. There is also some potential for exposure from water and soil. Chlorobenzene has been detected at low levels in surface, ground, and drinking water, but no information was found on levels in food. Since chlorobenzene binds, tightly to soil particles, skin contact with or ingestion of contaminated soil may be an important source of exposure, particularly in children living near hazardous waste sites. Additional studies would be useful to determine if soil-bound chlorobenzene is bioavailable. 

Anthocyanins can be absorbed intact as glycosides (Figure 1.1). The mechanism of absorption is not known however, PassamontP found that anthocyanins can serve as ligands for bilitranslocase, an organic anion membrane carrier found in the epithelial cells of the gastric mucosa, and suggested that bilitranslocase could play a role in the bioavailability of anthocyanins. Table 1.3 presents a summary of the research that has demonstrated absorption of intact anthocyanins in the rat, pig or human. At least 13 different anthocyanins from 7 different food sources have been observed to be absorbed intact and to be present in plasma or urine (Table 1.3). In... 

Pyridoxine is available from whole-grain cereals, peanuts, com, meat, poultry, and fish. Up to 40% of the vitamin may be destroyed, however, during cooking. Food sources contain all three forms, cither in their free form or phosphory-lated. Plants contain primarily pyridoxol and pyridoxaminc, while animal sources provide chiefly pyridoxal. Many plants also contain a glycoside of pyridoxol. which is included in vitamin content determinations. Although this conjugate is absorbed, it is not u.sed well. This may explain the lower bioavailability of the vitamin from plant sources than from animal sources. 

The bioavailability of iron from any source (e.g., iron supplement, food or meal composite) is considered to be that portion of the total iron which is metabolizable. Philosophically, this concept is important because the amount of iron utilized by avian and mammalian species is directly associated with iron need. When assaying iron bioavailability, it is therefore necessary to use an organism whose need will exceed the amount provided. In animal assays of iron bioavailability, iron need is assured by a growth phase and/or creation of iron deficiency through feeding an iron deficient diet and phlebotomy. Because healthy subjects are usually used in human assays of iron bioavailability (Cook et al., 1981 Cook and Monson, 1976 Radhakrishman and Sivaprasad, 1980), it is inappropriate to compare the data obtained from animal and human assays. In fact it is questionable if assays of iron bioavailability yield good information on the quantities of metabolizable iron available when healthy human subjects are used. 

Human intervention studies are ultimately necessary to determine the bioavailability of flavonoids from specific foods. A summary of recent studies including the doses, maximal plasma concentrations, and urinary excretion is shown in Table 2. There are large differences in the reported plasma levels among studies using seemingly similar food sources. The large interstudy variability cannot be explained by the doses used but may be explained by differences in experimental conditions and analytical methodology. 

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