Lipids and Wound Healing
Case reports suggest that certain types of fat, namely medium chain triglycerides (MCTs) and omega-3 fatty acids, may aid wound healing. Their potential mechanism of action is being examined in the growing field of immunonutrition, which looks at how key nutrients influence the body’s inflammatory response and response to catabolic stresses like surgery. After surgery, the body typically demonstrates an acute-phase inflammatory response, with return to normal function within a few days. Some individuals instead develop a systemic inflammatory response syndrome (SIRS), characterized by impaired wound healing. Whether altering the fat mix administered to patients can normalize the immune response and help resolve SIRS is under investigation.
Fat and inflammation
Fat has a metabolic relationship with the inflammation process. Omega-6 fatty acids, specifically arachidonic acid, are precursors for prostaglandin E2 (PGE2) and leukotriene B4(LTB4), bioactive compounds with inflammatory and vasodilatory effects. The inflammatory response catalyzed by these eicosanoids is necessary for wound healing. The recruitment, accumulation, and stimulation of fibroblasts are essential steps in normal wound healing and the formation of the extracellular connective tissue matrix. However, overproduction of prostaglandins and leukotrienes can lead to chronic inflammatory conditions and impairment of the healing process. Elevated levels of PGE2 can inhibit wound healing by blocking the proliferation of fibroblasts and inhibiting fibroblast chemotaxis.
In contrast, omega-3 fatty acids appear to be anti-inflammatory. Omega-3 fatty acids can suppress the metabolism of omega-6 fatty acids, reducing generation of prostaglandin E2 (PGE2) and altering T cell proliferative response. This may shift production of eicosanoids to a mixture that is less inflammatory and benefit wounds that are accompanied by persistent inflammation secondary to overactivity of macrophages. Omega-3 fatty acids also have been shown to stimulate cell migration in an experimental model of wound healing.3 It has been suggested that benefits of feeding omega-3 fatty acids include lower postoperative infection rates,4 restoration of normal tissue function postoperatively, and prevention of SIRS.
Experimental data
Researchers have studied the effects of individual types of fatty acids—omega-3 fatty acids (from fish oil), medium chain triglycerides (MCT), and long chain omega-6 fatty acids—on inflammation and wound healing. Japanese researchers fed one of two enteral formulas, very low fat elemental or 20 percent fat with a high percentage of MCTs, to rats with colitis;5 the high MCT formula had a stronger anti-inflammatory effect. Alexander and Gottschlich showed that an enteral formula with half its fat from fish oil and half from safflower oil reduced wound infection, shortened hospital stay, and reduced death in a group of burn patients, as compared to standard enteral formulas.6 In an animal study, Teo and colleagues reduced postburn protein catabolism in rats by feeding an enteral formula with lipids from MCT and fish oil.7 Lindgren and colleagues compared the effects on nitrogen balance between a lipid emulsion containing MCTs and a long chain emulsion in intravenously fed patients with sepsis or multiple injuries.8 Nitrogen balance improved in the MCT group, as compared to the long chain group.
In the absence of a large body of conclusive research, caution is encouraged. Inhibition of inflammation may disrupt the healing process for some wounds. In one animal study, wounds in rats fed a diet rich in fish oil, which is high in omega-3 fatty acids, had weaker wounds than did rats fed a diet rich in corn oil (omega-6 fatty acids).
The effects of lipids on inflammation and healing will be better understood as additional research is conducted using formulas with lipids in patients with impaired wound healing.
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