Gaining weight i.e. gaining weight requires eating more calorie dense foods such as cereals, meat containing fat and nuts. The most important thing you can do to gain weight, i.e., fattening up, is to consume more calories. In this case, every 1 gram of fat contains 9 calories, 1 gram of carbohydrates contains 4 calories and 1 gram of protein contains 4 calories. These three nutrients can provide calories for the body, and after proper conversion in the body, they can be converted into fat and stored, that is, to achieve the purpose of weight gain. Common foods that contain more of the three nutrients include carbohydrate-based cereals and fat- and protein-based meats. Nuts are also high in calories, which are rich in protein and fat. Trying to gain weight can also be done through fitness. Fitness can be a good way to gain weight by converting the protein you consume into muscle, and it is also a good way to build cardiovascular vigor and physical fitness, which is good for your health.