Unexplained weight loss can be caused by a range of diseases, like psychological illnesses, disturbances of the gastrointestinal (GI) tract, or problems with the thyroid gland. Conditions like cancer or its treatments, HIV, and some cardiovascular diseases are also associated with a sudden weight reduction. Alternately, many medications and illegal substances result in weight loss, too.
The reason why psychological illnesses are so closely associated with unexplained weight loss is because so many behavioral conditions can cause this symptom. Among these, depression may be the underlying reason for weight loss in a large number of cases. In addition, bipolar disorder, particularly in manic and hypomanic phases, and eating disorders like anorexia and bulimia are strongly associated with sudden weight loss. Substance abuse and even high stress are also potential culprits.
Ailments that affect the GI tract may provide an explanation for some unexplained weight loss, too. Persistent vomiting or even just nausea can mean food intake is too low to maintain weight. People are likely to mention severe GI problems to doctors. This gives physicians the opportunity to check for infections or to evaluate GI workings for problems like obstructions.
Another reason for unexplained weight loss could be dysfunction of the thyroid gland. Hyperthyroidism — excessively high amounts of thyroid hormone — speeds up the metabolism. This means people burn calories faster than they should and may lose weight even without attention to diet or exercising.
Alternately, the presence of cancer in an advanced stage may be heralded by unexplained weight loss. The initiation of cancer treatment very often leads to additional weight loss. Both chemotherapy and radiation may cause profound nausea and rob people of appetites, and the body itself may simply burn calories faster to fight cancerous cells.
HIV/AIDS or other autoimmune diseases can interfere with the way people eat or how their bodies metabolize food. This may result in unexplained weight loss, and in severe cases, it can cause a serious risk to health and survival. Some people with cardiovascular diseases also quickly lose weight because of the body’s inability to function efficiently. In other cases, heart disease creates excess water retention, and people gain weight quickly.
Disease and body dysfunction aren’t the only connections to unexplained weight loss. Using substances or taking medications to treat diseases may also cause this symptom. Some medicines destroy appetite, while others improve energy and prompt people to get more exercise. Another possibility is that a medication could result in GI side effects that make eating difficult.
Illegal substances or even legal ones like alcohol correlate to weight loss at times. Any form of methamphetamines is likely to greatly reduce desire to eat and simultaneously increase calorie burn. Extremely heavy drug use of most kinds, including of alcohol, tends to correlate to dramatically decreased body weight, whereas moderate use of drugs like alcohol or marijuana often causes weight gain.
