Consequences of inadequate fat intake on the healing wound

Healthy humans have the capacity to thrive on very diverse combinations and ratios of protein, carbohydrate, and fat. The same is basically true for the patient with a healing wound so long as energy requirements are adequately met. As discussed above, wound healing will occur for some wounds even in the presence of essential fatty acid deficiency. Wounds due to surgery without underlying trauma, or lacerations to cutaneous tissue appear to heal well independent of nutrition, although inadequate nutrition prior to surgery is a risk factor for a poor surgical outcome.132 On the other hand, the healing of pressure sores/ulcers and burns appears to be more sensitive to nutritional status.133 Clearly, there are different mechanisms at play for these different types of wounds. The first question, though, is under what scenario would there be inadequate fat intake? One likely cause is fat malabsorption. Fat malabsorption can be idiopathic, due to a number of diseases,134-136 or can be a consequence of intestinal surgery, such as a bowel resection.137 In these instances, it is possible for a patient to be in negative energy balance if sufficient calories are not supplied via protein and carbohydrate sources. A negative energy balance would impair wound healing and immune function and quickly lead to malnutrition in hypermetabolic patients. Another condition in which inadequate fat intake can occur is in patients receiving fat-free parenteral nutrition.138 139 In these instances, the glucose supplied by parenteral nutrition inhibits the release of fatty acids from adipose tissue, and patients can become essentially fatty acid deficient and manifest the scaly skin associated with EFAD. Elderly patients are also potentially at greater risk, because they appear to have a decreased ability to adjust their metabolism (e.g., resting energy expenditure) in response to lower caloric intake.140 There may be benefits to an "inadequate" fat intake for burn injuries. Immunosup-pression is a common outcome of burn-injured patients. A study in rats found that a low-fat diet (1% fat) compared to a high-fat diet (25% fat) prevented immunosuppression as measured by in vitro splenocyte proliferation.141 A followup study from the same laboratory group found that the type of fatty acid in the diet did not influence the degree of immunosuppression, and that nitric oxide release by macrophages was the cause of reduced T-cell activity.142

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