Causes:
Being underweight may result from Crohn's disease and other colon disorders, chronic diarrhea, diverticulitis, hyperthyroidism, intestinal parasites, malabsorption problem, some forms of cancer, and ulcerative colitis. Chemotherapy treatment, excess stress, surgery, significant loss, and trauma can all induce a loss of appetite, leading to weight loss. People with AIDS often experience a condition known as wasting syndrome, where body weight continues to be lost as the condition evolves. Intense exercise, particularly in marathon runners, can also lead to an underweight problem.
Some people are naturally more thin than others and may have a more active metabolism that reinforces their weight state. In this case, being labeled as medically "underweight" may be perfectly normal.
Being underweight may also be a sign of an underlying ailment or condition, particularly if the loss occurs quickly and without intent. Anorexia nervosa, bulimia, and other eating disorders can lead to situations of rapid weight loss.
