While a healthy appetite can reflect positive health, reduced or sudden loss of appetite may be a sign of any number or problems, with causes ranging from infection to stress. Additional potential causes include medications and emotional stress. If an underlying illness is present, symptoms may diminish once the illness is treated. In other cases, symptoms dissipate on their own or persist long-term. A health care provider should help ensure proper treatment to prevent complications.
A number of infections can trigger sudden loss of appetite. According to the University of Illinois Medical Center at Chicago, infections associated with loss of appetite include pneumonia, a respiratory infection that affects the lungs; hepatitis, inflammation of the liver; HIV/AIDS; influenza; and pyelonephritis, a type of kidney infection.
Various diseases can trigger sudden loss of appetite. According to the "The Merck Manual of Medical Information: Second Edition," digestive diseases such as irritable bowel syndrome, Crohn's disease, celiac disease, colitis and colon cancer can cause loss of appetite due to inflammation in the digestive tract, intestinal blockage or other factors. Kidney, liver and heart disease can also reduce the appetite. In some cases, sudden loss of appetite occurs at an advanced stage illness, such as congestive heart failure or kidney failure.
Psychological diseases including depression, anxiety disorder and schizophrenia can also cause sudden loss of appetite, particularly if symptoms of the underlying disease increase suddenly.
Sudden loss of appetite may occur as a side effect of certain medications. Examples include stimulant medications used to treat attention deficit hyperactivity disorder and weight loss drugs. According to the White House Initiative on Educational Excellence for Hispanic Americans, illicit street drugs such as amphetamines, hallucinogenics, inhalants and LSD can also trigger loss of appetite.
Sudden loss of appetite can also occur from heightened emotional stress. Losing a loved one, losing a job, divorce and positive stressors, such as weddings, falling in love and other significant events can cause sudden loss of appetite. Depending upon the situation and a person's ability to manage stress, loss of appetite may occur temporarily or endure while the stress level remains consistent or increases. Since loss of appetite can signify an emotional illness, such as depression, the University of Illinois Medical Center suggests professional guidance if symptoms persist.