unintentional weight loss is when a person loses weight without trying. it can be a symptom of some types of cancer. stress can cause unintentional weight loss. stress can come from divorce, changing jobs or over the loss of a loved one. once the stress is removed and the person feels happier again, the weight may return to normal. depression may also cause weight loss. eating disorders such as anorexia or bulimia can cause significant weight loss. these disorders usually require the help of health care professionals.