Anorexia can be defined in certain ways, such as not eating enough caloric intake to sustain life, in some cases not eating at all.  But it’s a severe eating disorder with a number of signs and symptoms.  First of all, the most obvious sign would be a sudden and severe case of weight loss.  Second, there is often a severe obsession with weight and the misconception of obesity or an overweight condition when they are actually severely and obviously underweight or even at a healthy weight. 

Some lie about what they eat or even pretend to eat in front of people, purging afterward in many cases.  Others only eat one food, so yes if you are on a diet that requires you only eat one food or otherwise, you would technically be considered to be anorexic.  There are often rituals surrounding eating and exercise, and compulsive exercises are likely. 

As far as side effects go, many are likely to experience weakness, dizziness, fainting, fatigue, depression, anxiety, low blood pressure, slow or irregular heartbeat, infertility, no periods, weakened hearts, kidney disease, or liver disease among others.  But all in all, it’s important to recognize anorexia early so that greater treatment can be possible.