Anorexia nervosa is an eating disorder characterized by attempts to lose weight, to the point of starvation. A person with anorexia nervosa may exhibit a number of signs and symptoms, the type and severity of which may vary and may be present but not readily apparent.

Anorexia nervosa, and the associated malnutrition that results from self-imposed starvation, can cause complications in every major organ system in the body. Hypokalaemia, a drop in the level of potassium in the blood, is a sign of anorexia nervosa. A significant drop in potassium can cause abnormal heart rhythms, constipation, fatigue, muscle damage and paralysis.

Symptoms may include:

- A low body mass index for one's age and height.

- Amenorrhea, a symptom that occurs after prolonged weight loss; causes menses to stop, hair becomes brittle, and skin becomes yellow and unhealthy.

- Fear of even the slightest weight gain; taking all precautionary measures to avoid weight gain or becoming "overweight".

- Rapid, continuous weight loss.

- Lanugo: soft, fine hair growing over the face and body.

- An obsession with counting calories and monitoring fat contents of food.

- Preoccupation with food, recipes, or cooking; may cook elaborate dinners for others, but not eat the food themselves or consume a very small portion.

- Food restrictions despite being underweight or at a healthy weight.

- Food rituals, such as cutting food into tiny pieces, refusing to eat around others and hiding or discarding of food.

- Purging: May use laxatives, diet pills, ipecac syrup, or water pills to flush food out of their system after eating or may engage in self-induced vomiting though this is a more common symptom of bulimia.

- Excessive exercise including micro-exercising, for example making small persistent movements of fingers or toes.

- Perception of self as overweight, in contradiction to an underweight reality.

- Intolerance to cold and frequent complaints of being cold; body temperature may lower (hypothermia) in an effort to conserve energy due to malnutrition.

- Hypotension or orthostatic hypotension.

- Bradycardia or tachycardia.

- Depression, anxiety disorders and insomnia.

- Solitude: may avoid friends and family and become more withdrawn and secretive.

- Abdominal distension.

- Halitosis (from vomiting or starvation-induced ketosis).

- Dry hair and skin, as well as hair thinning.

- Chronic fatigue.

- Rapid mood swings.

- Having feet discoloration causing an orange appearance.

- Having severe muscle tension + aches and pains.

- Evidence/habits of self harming or self-loathing.

- Admiration of thinner people.

Interoception has an important role in homeostasis and regulation of emotions and motivation. Anorexia has been associated with disturbances to interoception. People with anorexia concentrate on distorted perceptions of their body exterior due to fear of looking overweight. Aside from outer appearance, they also report abnormal bodily functions such as indistinct feelings of fullness. This provides an example of miscommunication between body and brain. Further, people with anorexia experience abnormally intense cardiorespiratory sensations, particularly of the breath, most prevalent before they consume a meal. People with anorexia also report inability to distinguish emotions from bodily sensations in general, called alexithymia. In addition to metacognition, people with anorexia also have difficultly with social cognition including interpreting other’s emotions, and demonstrating empathy. Abnormal interoceptive awareness like these examples have been observed so frequently in anorexia that they have become key characteristics of the illness.