Macronutrients metabolism

Biotin is a covalently bound coenzyme for acetyl-CoA carboxylases 1 and 2, 3-methylcrotonyl-CoA carboxylase, propionyl-CoA carboxylase and pyruvate carboxylase, which play essential roles in macronutrient metabolism. 

Stable isotopes are non-radioactive atoms of the same chemical element, which differ only in their number of neutrons [19]. Many elements also have radioactive (non-stable) isotopes. The most commonly used stable isotopes in studies of macronutrient metabolism are (D or deuterium), C, and 0, while Mg, Mg, a, Ca, Ca, Fe, Fe, Zn, and °Zn are the most commonly used stable isotopes for studies of mineral metabolism. The most commonly used radioactive isotopes are and (tritium) [19]. More than 6(X)0 stable isotope-labeled compounds (tracers) are commercially available for use in metabolic studies. Examples for some of these tracers are [1- C] leucine, [1- C, N] leucine, [ring- Hj] phenylalanine, and [6,6]-D2 glucose. It is currently accepted that these compounds have neghgible biological side-effects, which renders them ethically acceptable for use in children [20]. 

The commercial availability of stable isotope ( C, N, H)-labelled compounds and highly accurate mass spectrometers has made it possible to probe the details of metabolic pathways involved in macronutrient catabolism and neogenesis. This paper highlights aspects of animal nutrition and metabolism in which uniformly C-labelled [U- C] substrates and C-massisotopomer distribution approaches have been applied to investigations of amino acid and carbohydrate synthesis and catabolism. We will focus on the application of [U- C] substrates as tracers in chickens, fish, sheep, and cells in culture to quantify rates of macronutrient synthesis, identification of the sources of dietary nutrients that serve as substrates for neogenesis of macronutrients, and investigations of the intercormectivity of the pathways of macronutrient metabolism with those of the Krebs cycle to preserve metabolic flexibility via anaplerotic and cataplerotic sequences. 

The use of foods by organisms is termed nutrition. The ability of an organism to use a particular food material depends upon its chemical composition and upon the metabolic pathways available to the organism. In addition to essential fiber, food includes the macronutrients—protein, carbohydrate, and lipid—and the micronutrients—including vitamins and minerals. 

Figure 14.4 Schematic diagram comparing the bulk and molecular schemes for the metabolic fate of macronutrient components between diet and consumer tissues...

Both macronutrients (i.e., water, protein, dextrose, and IV fat emulsion [IVFE]) and micronutrients (i.e., vitamins, trace elements, and electrolytes) are necessary to maintain normal metabolism. 

Metabolic Abnormalities Associated with Parenteral Nutrition Macronutrients... 

The energy generated by metabolism of the macronutrients is used for three energy-requiring processes that occur in the body resting metabolic rate, thermic effect of food (formerly termed specific dynamic action), and physical activity. 

Among other things, the liver is responsible for the metabolism of carbohydrate, lipid and protein these processes are all interlinked, and Figure 2.1 outlines their relationships. The biochemical pathways involved in the metabolism of each of these macronutrients will be dealt with in turn. 

The nutritional characteristics of DAG oil (>80%) have been compared with dietary TAG of similar fatty acid composition. In particular, the 1,3-DAG isoform appears to have distinct metabolic characteristics that can impact postprandial lipid metabolism and use of macronutrients for energy compared with TAG. 

The following review focuses on experimental data supporting different metabolic characteristics of 1,3-DAG or DAG oil containing 1,3-DAG (Table 2). Relevant areas of observed differences between 1,3-DAG/DAG oil and TAG/TAG oil metabolism include postprandial lipid metabolism and use of macronutrient fuels. Observations from animal and human experimental data are included. 

Leibowitz, S. F. (1992). Neurochemical-neuroendocrine systems in the brain controlling macronutrient intake and metabolism. Trends Neurosci. 15, 491-497. 

As we have seen, trace metals are involved as cofactors of metalloenzymes and proteins, in all general metabolic processes of phytoplankton, including photosynthesis and respiration, and in assimilation of macronutrients. The vertical profiles of trace metal concentrations in open oceans (Figure 10.9) are like those of macronutrients that is, they show surface depletion resulting from algal uptake and partial release at greater depth due to mineralization. 

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