Starve a fever and feed a cold: feeding and anorexia may be adaptive behavioral modulators of autonomic and T helper balance

Anorexia is a common symptom accompanying infections, but the teteology of the phenomenon remains unexplained. We hypothesize that anorexia may represent a prehistoric behavioral adaptation to fight infection by maintaining T helper (Th)2 bias, which is particularly vital in fighting bacterial pathogens. Specifically, we propose that anorexia may avert the reduction of Th-2/Th-1 ratio by preventing feeding-induced neurohormonal, and vagal output from the gut. Emerging evidence suggests that the vagat and neurohormonal output of the gut during feeding promotes Th-1 function, which is desirable in fighting viral infections. Since fever may be an adaptation to fight bacteria and "colds" are generally viral in origin, the adage "starve a fever and feed a cold" may reflect a sensible behavioral strategy to tilt autonomic and Th balance in directions that are optimal for fighting the particular type of infection. The ability to modulate T helper balance through the neurohormonal and autonomic axis by adjusting food intake may be the mechanism behind other unexplained clinical observations such as the improved outcomes of ICU patients after enteric versus parenteric feedings. Compared to the prehistoric period when bacterial infection was commonplace, the anorexic response may be less adaptive today when viruses and cancers have become common triggers of anorexia. By promoting host anorexia, cachexia, and insomnia, cancers and viruses can deter behaviors such as digestion and steep that would raise vagal and Th-1 activity against tumors and viruses. Hydration and steep, unexplained but widely accepted recommendations for flu patients, may also work by promoting vagal and Th-1 functions. Modulating feeding, hydration, and steep may prove beneficial in treating other conditions associated with abnormal autonomic and Th balance. (c) 2004 Elsevier Ltd. All rights reserved.