There are many other causes of unexplained weight loss like worms in stool, depression, anorexia nervosa, AIDS, cancers especially colon cancers, drug abuse, infections and loss of appetite
. Loss of appetite
can again be due to certain medications, drug abuse, depression, AIDS, acute and chronic infections, eating disorders, cancers and hypothyroidism. Either you do not eat well or there is increased metabolism as in hyperthyroid states, HIV, cancer etc.