Polyphagia
Polyphagia or hyperphagia is an abnormally strong, incessant sensation of hunger or desire to eat often leading to overeating. In contrast to an increase in appetite following exercise, polyphagia does not subside after eating and often leads to rapid intake of excessive quantities of food. Polyphagia is not a disorder by itself; rather, it is a symptom indicating an underlying medical condition. It is frequently a result of abnormal blood glucose levels (both hyperglycemia and hypoglycemia), and, along with polydipsia and polyuria, it is one of the "3 Ps" commonly associated with uncontrolled diabetes mellitus.

Etymology and pronunciation
The word polyphagia () uses combining forms of poly- + -phagia, from the Greek words πολύς (polys), "very much" or "many", and φαγῶ (phago), "eating" or "devouring".

Underlying conditions and possible causes
Polyphagia is one of the most common symptoms of diabetes mellitus. It is associated with hyperthyroidism and endocrine diseases, e.g., Graves disease, and it has also been noted in Prader-Willi syndrome and other genetic conditions caused by chromosomal anomalies. It is only one of several diagnostic criteria for bulimia and is not by itself classified as an eating disorder. As a symptom of Kleine–Levin syndrome, it is sometimes termed megaphagia.Knocking out vagal nerve receptors has been shown to cause hyperphagia.Changes in hormones associated with the female menstrual cycle can lead to extreme hunger right before the period. Spikes in estrogen and progesterone and decreased serotonin can lead to cravings for carbohydrates and fats. These can be all part of premenstrual syndrome (PMS).According to the National Center for Biomedical Information, polyphagia is found in the following conditions:
Chromosome 22q13 duplication syndrome
Chromosome 2p25.3 deletion (MYT1L Syndrome)
Chromosome Xq26.3 duplication syndrome
Congenital generalized lipodystrophy type 1
Congenital generalized lipodystrophy type 2
Diabetes mellitus type 1
Familial renal glucosuria
Frontotemporal dementia
Frontotemporal dementia, ubiquitin-positive
Graves disease
Hypotonia-cystinuria syndrome
Kleine-Levin syndrome
Leptin deficiency or dysfunction
Leptin receptor deficiency
Luscan-lumish syndrome
Macrosomia adiposa congenita
Mental retardation, autosomal dominant 1
Obesity, hyperphagia, and developmental delay (OBHD)
Picks disease
Prader-Willi syndrome
Proopiomelanocortin deficiency
Schaaf-yang syndrome

Polyphagia in diabetes
Diabetes mellitus causes a disruption in the bodys ability to transfer glucose from food into energy. Intake of food causes glucose levels to rise without a corresponding increase in energy, which leads to a persistent sensation of hunger. Polyphagia usually occurs early in the course of diabetic ketoacidosis.  However, once insulin deficiency becomes more severe and ketoacidosis develops, appetite is suppressed.

See also
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Diseases and conditions associated with Polyphagia