Macronutrients provide the energy for all body functions as well as the major building blocks for all tissues and reparative processes (Table 1.2). As will be discussed in Chapter 2 and Chapter 3, carbohydrate and fat may both be used to support the energy needs of the organism, although certain cells may be obligate carbohydrate consumers. This is especially true in the healing wound, with a density of inflammatory cells and fibroblasts that use carbohydrate as an energy source.35 36 Studies suggest that, even when carbohydrates are readily available, a substantial percentage of the total energy needs are met by fat.37 These findings are discussed in greater detail in Chapter 3 and Chapter 11. In addition, fats provide the building blocks for the cell membrane and certain inflammatory mediators. Carbohydrates may minimize the burden for fat intake by providing substrate for fatty acid synthesis, except for essential fatty acids that must be obtained from dietary sources.
Protein is the third component of macronutrients. Amino acids provide the major structural building blocks of all proteins in the body, including collagen, the major protein of the healing wound. Amino acids are necessary for the cell membrane and enzymes and cytokine production in the healing wound. In the inflammatory and proliferative phases, amino acid requirements in the wound will be maximal due to the high level of enzymatic activity and the high rate of cell turnover.
Protein metabolism is closely interrelated to carbohydrate and fat metabolism. Glucose and fatty acid metabolites may be used as substrate for endogenous amino acid synthesis (Figure 1.4). Conversely, metabolites of amino acid breakdown may be deaminated to provide gluconeogenic precursors and substrate for fatty acid production. However, much like the fatty acids that cannot be synthesized by the human body, certain amino acids are essential or conditionally essential and must, therefore, be obtained through the diet. This concept is discussed in greater detail in Chapter 4.
Micronutrients function primarily as cofactors in biochemical reactions and, as such, are critical to all of the activities of macronutrients. Protein synthesis cannot continue without adequate quantities of vitamin B6, zinc, and copper.26,37,38 Collagen synthesis will be impaired without vitamin C, iron, and copper. Carbohydrate utilization is impaired without chromium and manganese. Vitamin B12, folate, and zinc are essential for nucleic acid metabolism and, thus, are essential in the healing wound with rapid cellular proliferation.
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