This syndrome is fairly common in obese persons.

Experts have evidence that Night Eating Syndrome (NES), in which over 50% of daily food intake is consumed after 8 p.m., may be related to stress rather than hunger or other emotional factors.

While NES is fairly uncommon in the general population (it is estmated to affect between 1 and 2% of adults), studies show that it may occur in up to approximately one-fourth of obese persons. NES was first described in 1955 and is characterized by:

• lack of or decreased appetite during the day
  
• insomnia
  
• morning anorexia--or not eating anything all morning
  
• consume fewer than average calories throughout the day.
  
• increased appetite at night
  
• evening hyperphagia (increased eating) and nocturnal eating (arising to eat after having gone to bed)
  
• worsening mood and depression as the evening progresses
  
• the tendency to eat carbohydrate-rich foods such as sugars and starchy foods.

In contrast to binge eating disorder, which is characterized by short intense bursts of eating, NES sufferers generally eat continuously throught the evening and night. The causes of NES have not been understood, and it has been thought to result from a combination of environmental and biological factors.

Researchers in Norway studied the neuroendocrine patterns and stress hormone levels in a small group of women with NES and compared these to normal controls. The doctors injected the study participants and controls with a dose of the hormone CRH*, which stimulates the body's stress response, and measured the levels of hormones ACTH* and cortisol* in response to this trigger. In the night eaters, the stress response - as measured by the secreation of ACTH and cortisol following CRH injection - was distinctly attenuated. CRH-induced ACTH levels were down 47% and cortisol levels were decreased by 71% in the night eaters.

These findings, published in the February 2002 issue of the American Journal of Physiology - Endocrinology and Metabolism, suggest that a disordered stress response, characterized by a reduced pituitary-adrenal stress reaction, may be a cause of NES. An abnormal pituitary gland function has also been detected in several other disorders such as insomnia, chronic fatigue syndrome, eating disorders, and other mood disruptions.

Reference:

Birketvedt GS, Sundsfjord J, Florholmen JR. Hypothalmic-pituitary-adrenal axis in the night eating syndrome. Am J Physiol Endocrinol Metab 2002 Feb;282(2):e366-9.


Glossary

• ACTH - a hormone secreted by the pituitary gland at the base of the brain, which acts directly on the adrenal glands to increase their secretion of cortisol and other hormones. In stress situations, ACTH levels rise, causing elevated cortisol levels. ACTH levels are controlled by the so-called hormone releasing factor CRH (corticotropin releasing hormone) from the hypothalamus of the brain.
  
• cortisol - a steroid hormone secreted by the outer portion, or cortex, of the adrenal glands. Any type of physical or mental stress can increase the production and release of cortisol, and this hormone is often called the "stress hormone" due to its increased secretion during stress responses in the body. Cortisol has a strong anti-inflammatory effect, and it increases mobilization of amino acids from muscle (increasing protein breakdown), increases mobilization of fatty acids (increasing lipid concentrations in the blood), and increases blood glucose concentration.
  
• CRH - so-called "releasing factor" made and released from the hypothalamus of the brain, which is carried to the pituitary gland, where it causes secretion of ACTH (the hormone that triggers cortisol secretion from the adrenal glands).

http://stress.about.com/library/weekly/aa021902a.htm