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I've heard of anorexia nervosa being a severe loss of appetite. I'm wondering what causes such disease in humans?

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    $\begingroup$ People with anorexia usually tend to have high levels of cortisol, the brain hormone most related to stress, and decreased levels of serotonin and norepinephrine, which are associated with feelings of well-being. But you may want to ask this question on the Cognitive Sciences Stack exchange $\endgroup$ – Ebbinghaus Feb 15 '16 at 19:45
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    $\begingroup$ Definitely a good target for CogSci, but dependent on the answer also here. If @gone.'s comment holds, it's definitely ontopic here too. One way or another, nice question +1 $\endgroup$ – AliceD Feb 15 '16 at 20:53
  • $\begingroup$ "Is there a physiological underpinning for anorexia?" would be on topic here. "Why do people become anorexic?" might be more cogsci. It's semantics though and I like the question. +1 $\endgroup$ – James Feb 16 '16 at 4:56
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What is anorexia nervosa?

Generally, it is an eating disorder which is characterised by a tremendous fear of food as well as an extreme weight loss. Patients with anorexia nervosa do not necessarily lose their appetite but rather obsessively control and restrict their food intake.


Anorexia Nervosa as an inherited disease/genetic factors

There has been a lot of research proposing that eating disorders are often biologically inherited and tend to run in families.

Recent research suggests that inherited biological and genetic factors contribute approximately 56% of the risk for developing an eating disorder. Individuals who have a mother or a sister with anorexia nervosa are approximately twelve times more likely to develop anorexia and four times more likely to develop bulimia than other individuals without a family history of these disorders. Studies of twins have shown a higher rate of eating disorders when they are identical (compared to fraternal twins or other siblings).


The hormone serotonin

There has been found that anorexics have an overproduction of serotonin, which can cause a continual state of acute stress and anxiety.

Researchers are still puzzled as to why, if anorexics already have high levels of serotonin, then SSRIs (medications like Prozac which raise serotonin levels) are successful treatments for some individuals. These scientists speculate that that there may be different subtypes of this disease, and that different groups of anorexics may have different neurochemical characteristics.

Researchers have also noted that abnormal eating behaviours and the resulting changes in the body can actually cause a disruption in serotonin levels, thus contributing to an already existing problem. Abnormalities in serotonin levels can lead to depression and anxiety. Studies also suggest that there are genetic predispositions to serotonin disruptions that appear to run in some families.


The hormone dopamine

Research suggests that women who develop anorexia nervosa may have altered levels of dopamine in their brains. Dopamine disturbances can cause hyperactivity, repetition of behaviour (such as food restriction), and anhedonia (a decreased sense of pleasure). This neurotransmitter also affects reward-motivated behaviour.


The hormone cortisol/hydrocortisone

Numerous other hormones in the brain have also been linked to eating disorders. Stress triggers the production and release of a hormone called cortisol; chronically elevated cortisol levels have been observed in patients with anorexia. Cortisol can inhibit appetite.


The hormone leptin

Leptin is a protein hormone produced by the body's adipose tissue. Leptin is regarded as a hormone which can regulate fact storage and appetite. If individuals with anorexia nervosa lose extreme amounts of body fat, their levels of leptin drop which is known as hypoleptinaemia. The side effects of hypoleptinaemia can include amenorrhea, impaired metabolism, and bone loss.

Also, if people receive treatment, their leptin levels do not immediately return to normal. Initially during the treatment, leptin levels rise through the sky, which is also the reason why most patients are most susceptible of relapsing back into an eating order, since very high levels of leptin may cause a weight gain.


Sources:

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