If you want to gain weight then gradual weight gain advisable. Also calculate your body mass index (BMI). (BMI) below 18.5 is underweight. BMI is calculated by formula = Weight in Kilograms / (height in meters x height in meters). If it is in normal range then there is no need to gain weight. There are various causes of underweight like inadequate food intake, prolonged meal time gaps, and increased physical activity weight increasing food intake. Advice 1. Start workout in gym at least for half an hour for 4 – 5 days in a week regularly. Start with a balanced mix of cardio, weight training and flexibility exercises 2. Take natural high protein like egg, soya bean, pulses, meat, and milk. Choose food with nutritional calories like potato, banana and dry fruits 3. Drink 3 – 4 liters of water daily 4. Chew the food properly to make it easily digestible 5. Avoid excess intake tea and coffee after meal as they contain tannin which hinders absorption of minerals like iron I hope this information will help you. I will be happy if you ask another question Thank