Being underweight can happen due to fast metabolism, low appetite, poor dietary intake, stress, digestive issues, or sometimes underlying health problems like thyroid imbalance or nutrient deficiencies. The goal of healthy weight gain is not just eating more, but eating balanced, nutrient-rich food that helps build muscle and strength instead of only fat. Try increasing your meal frequency by having small, calorie-dense meals every 2-3 hours, and include foods like rice, chapati, potatoes, nuts, peanut butter, dairy products, eggs, lentils, and healthy oils in your diet. Adding protein is important because it helps in muscle growth and improves body strength. Light strength exercises or resistance training can also help convert extra calories into healthy muscle rather than fat. Proper sleep and stress control are equally important because poor rest can affect appetite and metabolism. If weight is not improving despite a good diet or if there are symptoms like fatigue, diarrhoea, or appetite loss, it is important to get a medical check-up to rule out underlying causes.