Snacking between meals. The most common cause. You eat cookies, sandwiches, etc. between meals, so in due time You don't want to eat. In fact, loss of appetite as such in this case, you do not eat food at the wrong time, and you need to revise diet.
Emotional state. Stress, grief, depression, napadenie, boredom, loneliness can cause loss of appetite – You either completely forget about eating or trying to eat, but can not, because too nervous.
This category of reasons can be attributed to the severe psychological trauma: depression, nervous anorexia, schizophrenia.
Drugs. Loss of appetite can be caused by taking various drugs: preparations containing digitalis; antibiotics; rhinitis medications that contain FDA; pain; diabetes medication; anesthetics; drugs for chemotherapy.