Starving for nutrients: reconciling the paradox of anorexia during infection – Blaxter Award Winner Lecture

Questions posed at a higher level, such as at a whole-body metabolism level, can help us to achieve understanding of functional mechanisms, as opposed to understanding of causal mechanisms of biological phenomena, i.e. why something happens as opposed to how it happens. In my lecture I will use the example of pathogen-induced anorexia as an example to support my proposition. By relating the existence of such anorexia to the outcomes of infection, it is possible to put forward hypotheses about the occurrence of a rather paradoxical phenomenon and suggest how we should be treating the anorectic host during the challenging phases of an infection. A voluntary reduction in the feed intake of animals and humans is considered an ‘unavoidable’ characteristic of most infections. I call this reduction: pathogen-induced anorexia. Pathogen-induced anorexia constitutes a ‘paradox’: it occurs at times when infected host requirements for nutrient resources are increased, rather than decreased. Pathogens divert resources away from their host and in response to infection hosts initiate resource-demanding processes, such as the immune response and the repair of the damage caused by the pathogen. There is now ample evidence to suggest that anorexia is linked to the existence of an immune response to an infection. Given this, it is reasonable to suggest that host nutrition may affect the features of anorexia (timing, duration, extent) through its effects on the immune response. Evidence suggests that over-supply with nutrient resources seem to penalise the outcome of the infection in infected animals and humans. A corollary of this is that infected host seem to target a nutrient resource intake, which appears to be beneficial for infection outcomes, whilst at the same time they avoid excess of nutrient resource intake. This is achieved through the features of anorexia and the expectation is that such features will be affected by diet composition. During my lecture, I will present evidence from recent experiments about the relationship between food composition, anorexia and infection outcomes in mammals and birds, to support this proposition. Understanding which nutrient resources are targeted by infected hosts and the consequences of this on the outcomes of the infection, will have implications on how hosts should be fed during the critical stages of an infection.

What will I learn?

• Gain knowledge on the link between anorexia and immune response to infection
• Understand the relationship between food composition, anorexia and infection outcomes in mammals and birds
• Analyse which nutrient resources are targeted by infected hosts and the consequences and implications