We speculate that sickness behaviors, and particularly anorexia induced by systemic infection (a metabolic adaptation that is essential for organismal tolerance to systemic inflammation (Wang et al, 2016)), impose metabolic constraints in the bone marrow microenvironment possibly because of reduced cytokines (e.g., SCF) or nutrient availability (e.g., glucose, amino acids) that may enforce an upper limit to the rate of myeloid cell production. This evidence concerns the gene KITLG and Anorexia.