Abstract
The potential immunosuppressive effects of lipids high in the n-6 polyunsaturated fatty acids (PUFA) have led many clinicians to recommend limiting fat intake in stressed patients. Similarly, experimental and clinical evidence has been presented that supports the use of lipid formulations enriched in the marine-based n-3 PUFA in these patients.1,2
This paper describes an experimental study designed to address the effect of dietary fat composition on outcome in an animal model of chronic intra-abdominal sepsis. Guinea pigs underwent gastrostomies and were later implanted with osmotic pumps inoculated with a mixture of Escherichia coli and Staphylococcus aureus. A steady infusion of this synergistic combination of bacteria into the peritoneal cavity resulted in an animal model of chronic intra-abdominal sepsis. Animals were randomized to one of three dietary groups according to the level of fat intake: 3.5%, 14%, and 56% of total calories. Within each of these groups, fat composition was either high in n-6 PUFA (100% Microlipid), high in n-3 PUFA (100% maximum eicosapentaenoic acid [MaxEPA]) or a 50:50 mixture of the two.
Animal survival was not significantly altered by the amount of fat in the diet (Kruskal-Wallis analysis of variance, p > .1). However, the dietary fat composition had a significant overall effect (p < .05) on the length of survival. Median survival in the 50:50 group was 12.5 days, significantly longer than that in the 100% MaxEPA group (9 days), p = .011), but not significantly longer than that in the 100% Microlipid group (10 days, p = .082).
In another experiment animals were fed a 14% total fat calorie diet. A total of five subgroups were created, with fat ratios (Microlipid/MaxEPA) of 100/0, 25/75, 50/50, 75/25, and 0/100. Survival was greatest in the group of animals given equal amounts of fat types: 18%, 25%, 84%, 42%, and 36% (p = .023, 50:50 group vs all other groups).
No major differences in immunologic parameters among the various groups were noted, except for an increase in lipopolysaccharide-stimulated prostaglandin E2 production by splenic macrophages in the 100% Microlipid group (p = .03).
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