###Human: I have lost 5 kg in one year. What is the problem behind it? ###Assistant: Keyword - Unexplained weight loss Hi. You are having a weight loss of five kilograms in one year. It can be due to anxiety, over-exercise, and due to less food intake than a requirement. You can rule out such common cause if it is present. If this is not the issue, then investigate with serum TSH (thyroid stimulating hormone) estimation to rule out hyperthyroid. You can do test for HIV using Elisa, and fourth generation testing if it is suspected. You can do a chest X-ray to rule out any lung problem if it is present. Any chronic infection can also lead to weight loss. So provide your history if it is present. You can consult a physician for a physical examination.