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The Main Food Substrates
Most food components are macromolecules. Food macromolecules are biological polymers (i.e., chains of repeating units of smaller molecules linked together) and are comprised of proteins, nucleic acids, carbohydrates (polysaccharides), and lipids. The repeating units forming macromolecules are called monomers, or building blocks. The monomers in proteins are amino acids, those in polysaccharides are sugar derivatives, (example: hexoses such as glucose or fructose, or pentoses such as ribose). Those in nucleic acids are nucleotides. Lipids as major food components are not organized as proteins, i.e., in a repeating manner of monomers. Proteins, carbohydrates, and lipids constitute the main substrates for digestive enzymes as well as the oral enzymes supplied as dietary supplements.
Proteins are essential molecules used in all types of cellular activity and life. Enzymes, antibodies, regulatory molecules, contractile molecules responsible for movement, hormones, cellular structural components are some of a few of the proteins needed to sustain life. Almost all proteins in the body are in continuous dynamic: breakdown (catabolism) and formation (anabolism). Thus, in order to maintain vitality, viability, and health the body must have a supply of building blocks to help replenish the proteins that are broken down. Considering that even the proteins involved in regulating and making other proteins need also to be made and replenished, protein in the diet (i.e., amino acids) is an obligatory demand by the body.
Proteins contain different amino acids and in various proportions. Some amino acids may be absent or only in trace amounts in a particular protein. There are 20 amino acids of the L-configuration that are naturally found in the human body. Most of these amino acids can be synthesized in the body if the building blocks for their synthesis are available. These amino acids that the body can make on its own are called non-essential amino acids. However, there are nine amino acids that the human body cannot synthesize. These nine amino acids are said to be essential amino acids, and they must be provided in the diet and in adequate amount. These nine essential amino acids in human are:
*Histidine is an essential amino acid in the human child. Human adults acquire the ability to synthesize histidine, and thus, histidine is not considered an essential amino acid in adults.
In the synthesis of proteins, if one essential amino acid is missing, the cell will stop the process of synthesizing the protein, and the result is a truncated polypeptide. This is because the amino acid is not provided in the diet, and the cell cannot make it. Thus, because the lack of a single essential amino acid, a potentially vital protein will not be synthesized. This explains the importance of complete protein in the diet for health and vitality. A diet that does not include a complete protein will negatively impact wellness and health. A complete protein is a protein source that provides the body with the essential amino acids, i.e., the amino acids that the body cannot synthesize and that need to be included in the diet.
Additionally, proteins are needed to help provide the nitrogen necessary for the synthesis of other nitrogenous molecules, including the nonessential amino acids. This is accomplished by the proteins in the diet that the body breaks down into amino acids that can be incorporated into the building process of new molecules.
Any truncated, unfinished protein/polypeptide resulting from the lack of an essential amino acid as mentioned above will be broken down and its amino acids will be used for energy or to make fatty acids (ultimately fats). This incomplete synthesis of proteins will ultimately deprive the body of essential molecules. The amino groups (NH2) resulting from the amino acids of unfinished proteins will be used in the synthesis of other compounds and/or excreted as urea and other nitrogenous compounds. Additionally, undigested proteins may be used by organisms in the GI tract via other pathways to generate toxigenic compounds. An inadequate protein supply and/or digestion may ultimately result in impairment of vital functions, production of toxic compounds by bacteria, and genesis of poor health.
Carbohydrates also called polysaccharides are polymers of simple sugars such as glucose, fructose, and galactose in various combinations. The repeating units may be glucose, or fructose or a disaccharide of glucose plus another simple sugar. Carbohydrates are the main source of cellular energy important as energy sources, but also contribute in the synthesis of glycoproteins, proteoglycans, glycoplipids, and glycosaminoglycans.
Glycoproteins, proteoglycans, glycolipids, and glycosaminoglycans play a major role in cell functions and are involved in cell to cell recognition, cellular signaling, blood grouping elements, heparin, membrane structure, connective tissue, mucous secretions, and other compounds. Carbohydrates are also important in helping the body use fats as well as in removing foreign substances. However, any excess of dietary glucose is stored as glycogen and/or as fat.
Additionally, a deficit of glucose, either resulting from poor digestion or just inadequate diet supply, will impair the nitrogen balance. As result of a lack of carbohydrates to supply energy, the body will break down some tissues in order to use their proteins, albeit using constitutive proteins from muscles for instance, for energy. This use of protein for energy instead of anabolism and synthesis of vital molecules will impair the body's biosynthetic and defense mechanistic functions.
Lipids, commonly referred to as fats, constitute a heterogeneous group. The main classes of lipids are:
Natural edible fats contain mostly triglycerides and other substances such as phospholipids, sterols, vitamins, pigments, oxidation products, and traces of metals and in some cases toxic materials. As a group, lipids in the diet contribute as an energy source to the cell. Lipids are also important as they carry fat soluble vitamins and essential fatty acids to the cell. Fat soluble vitamins and essential fatty acids are necessary for the synthesis of various cellular and regulatory molecules. A fat-free diet will result in deficiency of essential fatty acids such as linoleic acid and linolenic acid. These two fatty acids cannot be synthesized by humans and need to be supplied in the diet. These essential fatty acids and others are supplied as esters in various forms of acylglycerols. For the body to obtain the fatty acids it needs, the esters have to be broken down and the fatty acids assimilated into the cells.
Thus the cell must provide all these required nutrients for synthesis to occur successfully. In order for the cell to accomplish that requirement, it relies on an adequate supply of food and its proper digestion. This implies several requirements: