Being very thin can happen due to fast metabolism, poor calorie intake, stress, irregular eating habits, lack of sleep, excessive physical activity, digestion problems, thyroid issues, or sometimes nutritional deficiencies. In some people, body type and family history also play a role. Gaining healthy weight usually takes time and works better with steady lifestyle changes rather than overeating junk food. Try eating 5-6 small balanced meals daily with enough protein and healthy calories. Foods like milk, curd, eggs, nuts, peanut butter, bananas, rice, potatoes, paneer, dry fruits, pulses, and healthy oils may help increase weight gradually. Strength exercises such as light gym training or resistance workouts can help build muscle instead of only fat. Good sleep and stress control are also important because poor sleep may affect appetite and body recovery. Avoid skipping meals and excessive smoking or alcohol if applicable. If you have loss of appetite, diarrhoea, weakness, fever, thyroid symptoms, or weight not increasing despite good eating habits, it is better to get checked by a doctor to rule out any underlying health condition.