Your body will start to use muscle and organs for protein, this is also true for lack of sugars. One can see in both instances that it is true, when noticing someone with malnutrition, arms and legs are very thin, but stomach is distended. Eventually you can wind up in shock (not temporary.
If you see someone nervously wringing their hands, you can assume they're worried about something. If you see someone crying, the obvious assumption is to believe they are sad about something.