There are no specific diseases that directly cause weight loss. However, several medical conditions can lead to unintended weight loss as a symptom. Here are some examples: Hyperthyroidism: An overactive thyroid gland can increase metabolism, leading to rapid weight loss despite a normal or increased appetite. Diabetes: Uncontrolled diabetes, particularly type 1 diabetes, can cause weight loss due to the body's inability to properly use glucose for energy. Cancer: Certain types of cancer, such as pancreatic, stomach, or lung cancer, can cause weight loss due to a combination of factors, including decreased appetite, changes in metabolism, and the body's response to the tumor. Gastrointestinal disorders: Conditions like celiac disease, Crohn's disease, ulcerative colitis, and chronic pancreatitis can interfere with nutrient absorption, leading to weight loss. Chronic obstructive pulmonary disease (COPD): This lung disease can make breathing difficult, resulting in increased energy expenditure and unintentional weight loss. Depression and anxiety: Mental health conditions can affect appetite and lead to changes in eating patterns, potentially resulting in weight loss. It's important to note that unintentional weight loss can be a concerning symptom and may indicate an underlying health issue. If you or someone you know is experiencing unexplained weight loss, it's advisable to consult a healthcare professional for a proper diagnosis and appropriate treatment.