What anorexia can do to your body
BMJ Group Medical Reference
Anorexia can be very harmful. It's more dangerous than bulimia. Starving your body of food and losing weight stops your body's organs working properly. It can damage your heart, kidneys, digestion, bones, muscles, and, if you're a woman, your ovaries. If one of these problems goes on for too long, you could die.
Some of the ways anorexia can hurt your body are listed below. You can see that anorexia really is serious. But some of these problems will get better if you start to gain weight.Effects on your heart and blood vessels
Effects on your bones, skin, and teeth
Having anorexia can affect your heartbeat and blood flow:    If you are too thin for your height (underweight), you can get low blood pressure and your heart might beat too slowly to get enough blood to the organs that need it.
If you don't eat and drink enough, your body will have too little water in it (get dehydrated). This can mean less blood flows around your body. You may feel dizzy and faint when you stand up.
Your heartbeat may become irregular. (Your doctor may say you have an arrhythmia.) Some types of severe arrhythmias can kill you if you don't get treatment straight away.
When you get treatment and start to recover from anorexia, you need to start eating again slowly. If you eat too much too fast, it can put a lot of strain on your body. There is even a risk that you can harm your heart. 
Effects on oestrogen and your fertility
Anorexia makes your body produce less of the hormone called oestrogen. Oestrogen helps bones stay solid and strong. If you have anorexia for a long time, your bones may weaken (you'll have low bone density). This causes the body to lose more bone than it can replace (called osteoporosis). If this happens, there's a risk that your bones will break easily and you may have fractures, especially when you're older.   
Making yourself vomit regularly can wear away the enamel on the surface of your teeth. You'll be more likely to get bad cavities.
You may lose your hair.
Your skin may dry out and turn yellowish.
Your fingernails and toenails may get brittle.
About a third of people with serious weight loss get fine, soft hair on their face and body.
If you are a woman with anorexia, your ovaries may stop producing a hormone called oestrogen. Your periods will become less regular or stop. This happens to 9 in 10 women with anorexia.  Your periods should start again when you put on weight.
If you are too thin for your height, you may have problems getting pregnant.  
If you have anorexia and you do get pregnant, you're more likely to have problems than someone who is a healthy weight. For example, if you don't eat enough, you have a greater risk of miscarriage (having your pregnancy go wrong and losing your baby). And if your baby doesn't get enough food while you're pregnant, it is more likely to be born too early (be premature) and to be small.  Small, premature babies are usually less healthy than larger babies who are born after the full nine months.  
If you've had anorexia for a long time, you're likely to have low levels of sugar in your blood. If this happens, you can feel weak, nervous, and irritable. And you can have bad headaches and trouble with your vision.
Anorexia can upset the delicate chemical balance in your body, especially if you make yourself sick or keep taking laxatives. If your body chemistry is upset too much, you can have problems (including heart failure) that could kill you.
Anorexia may mean you have less of a hormone called leptin. This hormone is made in fat cells. If you don't have enough of it, things can go wrong with the way your body keeps your weight stable, how your brain tells you to eat or stop eating, and how your body burns fat.
If you vomit or take laxatives regularly, you may have trouble digesting food. You might have stomach pains, diarrhoea, or constipation. For more information, see Problems caused by purging.