Immune: A Journey Into the Mysterious System That Keeps You Alive

by Philipp Dettmer

Why do you lose your appetite when you are sick? Well, you can blame the onslaught of cytokines that your immune system releases for that. The cytokines signal your brain that a serious defense is happening at that very moment that the body needs to conserve energy for. Because as you may imagine, mobilizing millions or billions of cells for a fight is a pretty resource-heavy operation. Digesting food actually requires a lot of energy too, so shutting these processes down is freeing up your system to focus on the defense. It also reduces the availability of certain nutrients in your blood that your invaders would love to get their tiny pathogenic hands on. This does not mean that you should actively try to starve out a disease. Not digesting is a short-term strategy not a long term solution and in chronically ill people, the lack of appetite can lead to dangerous weight loss. So if you feel hungry again you can eat something to refill your energy storage.