Model diets

Landrum et al. (1992) developed a kinetic bioaccumulation model for PAHs in the amphipod Diporeia, employing first-order kinetic rate constants for uptake of dissolved chemical from the overlying water, uptake by ingestion of sediment, and elimination of chemical via the gills and feces. In this model, diet is restricted to sediment, and chemical metabolism is considered negligable. The model and its parameters, as Table 9.3 summarizes, treat steady-state and time-variable conditions. Empirically derived regression equations (Landrum and Poore, 1988 and Landrum, 1989) are used to estimate the uptake and elimination rate constants. A field study in Lake Michigan revealed substantial differences between predicted and observed concentrations of PAHs in the amphipod Diporeia. Until more robust kinetic rate constant data are available for a variety of benthic invertebrates and chemicals, this model is unlikely to provide accurate estimates of chemical concentrations in benthic invertebrates under field conditions. 

Figure 22.5 shows cholesterol levels in the liver and serum of C57BL/6N mice after 4 weeks of feeding. Hepatic cholesterol accumulation and hypercholesterolemia were induced by the lipodystrophy model diet, and they were markedly attenuated by DHA supplementation. 

HMG-CoA reductase, a rate-limiting enzyme of cholesterol synthesis, and ACAT-1, a rate-limiting enzyme of cholesterol esterification, relate to hepatic cholesterol storage. Levels of mRNA of those enzymes were also increased by the lipodystrophy model diet during the onset of hepatic steatosis, but DHA supplementation attenuated this (Fig. 22.6). 

Another approach is the model diet where, based on consumer statistics, a diet is proposed that models that of the average or possibly (with adequate data) the non-average consumer. This is of value when limited consumption data exist or when the major source of contamination is one food group. This approach can be considered to be cost effective for a deterministic approach but is subject to errors when many foodstuffs are involved. If the groups for the model diets are based upon good and appropriate data then it may be possible to use model diets for different age groups or at risk groups. 

This chapter provides an overview of the various bubble and foam separation techniques. The overview inclndes not only the results of laboratory and larger-scale studies but also tbe mathematical models diet can be employed to optimize removal efficiencies atid predict removal behavior. 

Knockout mice have been reported for several FATPs [1]. As insulin desensitization has been closely linked to excessive fatty acid uptake and intracellular diacylgly-cerol and TG accumulation, these animal models were particularly evaluated in the context of protection from diet-induced type 2 diabetes ( Type 2 Diabetes Mellitus (T2DM)). In addition, studies on human subjects have also established genetic links between polymorphisms in FATP genes and metabolic alterations [1]. 

Krueger, H.W. and Sullivan, C.H. 1984 Models for carbon isotope fractionation between diet and bone. In Tumland, J.R. and Johnson, P.E., eds.. Stable Isotopes in Nutrition. Washington D.C, American Chemical Society Symposium Series, No. 258 205-220. 

White, C.D. 1997 Ancient diet at Lamanai and Pacbitun implications for the ecological model of collapse. In Whittington, S.L and Reed, D.M., eds.. Bones of the Maya Studies of Ancient Skeletons. Washington, DC, Smithsonian Institution Press 171-180. 

Hedges, R.E.M. and Van Klinken, GJ. 2000 Consider a Spherical Cow.. . . —On Modelling and Diet. In Ambrose, S. and Katzenberg, M.A., eds., Biogeochemical Approaches To Pakodietary Analysis. Kluwer Academic/Plenum Publishers, New York. 

Notwithstanding the possibility that some C4-based meat was consumed, the existing evidence for at least some C3-based meat in the diet of Mesoamerican (and other) peoples suggests that a routing model may lead... 

Some aspects of the biochemistry of metabolic processes affecting nutrients appear to have significant consequences for the expected behavior of stable carbon isotopes as tracers of diet. Specifically, we have seen that the simple model of a total scrambling of carbon atoms during endogenous biosynthesis is inconsistent with the expected pathways of some nutrients, whereas other isotopic records in ancient human tissues can be adequately accounted for by this model. 

The applicability of the linear-mixing model is seen most prominently in the interpretation of the 5 C of bone apatite which has been shown to represent the total diet, rather than being derived from energy foods , as was previously proposed by some authors. Although 5 C,p should represent total diet, the isotopic fractionation between this component and total diet appears to be somewhat variable, suggesting that more definite knowledge about this fractionation is needed if we are to use 5 C,p as an index of total dietaiy 5 C values. 

This paper explores how models may be developed to account for the relationship between the stable isotope composition of a body tissue of an organism and its diet. The main approach taken is to express this relationship as an explicit equation, or a DIFF , and then to show how the values of such a DIFF can be evaluated from published experimental data. These values can be expected to have a much wider meaning than a simple encapsulation of a particular experimental design. As a main example, we show how the values may be used to constract a metabolic model in which the synthesis of non-essential amino acid for collagen construction can be treated. A second example is to show how the evaluation, in terms of diet, of the spacing between collagen and carbonate 6 C may be put on a rigorous basis. 

The main part of the paper consists in first formulating a DIFF for a data set of body component isotopic compositions when fed on known diets, next developing a flow-model appropriate to this data set whose behaviour can then be compared with the DIFF Many of the issues raised in this process help to provide an understanding for the wider questions posed in the introduction. 

A simple application of the flow-model suggests why bioapatite carbonate 8 C values should directly follow the 8 C values for the diet as a whole. Experimentally, this observation seems to be generally confirmed (Ambrose and Norr 1993 Tieszen and Fagre 1993). In terms of the flow-model, it is... 

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