Table 141

Complications Relative to Loss of Lean Body Massa

Lean Body Mass Associated

(% Loss of Total) Complications (Related to Lost Lean Mass) Mortality (%)

10 Impaired immunity, increased infection 10

20 Decreased healing, weakness, infection 30

30 Too weak to sit, pressure sores, pneumonia, no healing 50

40 Death, usually from pneumonia 100

"Assuming no preexisting loss.

Priority for Protein Intake vs.

% Loss of Lean Tissue

10% Loss

Priority for Protein Intake vs.

% Loss of Lean Tissue

10% Loss

FIGURE 14.1 The wound takes priority for available nutrients as long as LBM loss does not exceed 10% of total. With increasing loss of lean body mass (LBM), more nutrients are used to restore lean mass while wound healing becomes markedly impaired until a portion of lost lean mass is restored.

Impaired Healing with Lean Mass Loss

Impaired healing is the result of the shunting of protein substrate away from the wound to be used instead for the restoration of lost lean mass. This process occurs with lean mass losses exceeding 15% of total1517 (Figure 14.1). This response is understandable, as the major risks for morbidity and mortality in moderate to severe protein energy malnutrition are complications caused by the loss of lean mass.1517

Altered Nutrient Partitioning

There are two nutrient compartments, one for energy production and the second for protein synthesis or lean body mass. The metabolic response, to "stress" or to PEM, produces an alteration in normal nutrient partitioning. The result is the inappropriate use of protein for energy.

Normal metabolic pathways, which generate sufficient energy to meet daily demands and for new protein synthesis, are tightly regulated. The size of the lean mass compartment is genetically defined, with adaptation by environmental stimuli. Macronutrients in the form of fat and carbohydrates are channeled into production of energy, with excess being deposited as fat.6-12

Protein consumed is digested and absorbed as peptides and amino acids to be used for protein synthesis, restoring and maintaining the lean mass. Normally, only 5% of the protein is used for energy and 95% for protein synthesis. However, if normal anabolic activity decreases or catabolic hormone activity increases, there is an escape of protein from the protein synthesis compartment to the energy compartment.7 This escape occurs when anabolic hormone levels are decreased, as in the elderly adult, and is the reason for the increased protein requirements in this population.1819 The same process occurs with activation of the stress response to injury,7-9 where up to 25% of available protein substrate is burned for energy.17-20 Anabolic hormone replacement can assist anabolic activity by directing protein substrate into

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