Protein is the major macro-nutrient that is responsible for building muscles and body tissues which simply means, you can’t gain weight without adding it to your diet. A gram of protein contains 4 calories, so if you eat protein on regular basis you can gain weight.
Another fact about protein is that your body can’t store protein, so you have to get it from foods (most preferred) every day.
In order to build muscles, instead of just gaining weight, you should add more foods that are high on protein. When you eat foods that contain protein, your body breaks them down into amino acids. Your body then can uses these amino acids to repair your body tissues or builds more muscles.
The reason why you need these protein rich foods, that are animal based protein, is that they’re quality protein. They contain all the essential amino acids that your body can’t make on its own. The only way to get them all is from animal protein foods only, not plant based protein.
However, the main force behind gaining weight is not protein alone. Protein is just one part of the whole story. What you basically need is to eat more calories than you burn, which means that the total calories you eat from foods should exceed what your body uses on daily basis.
Protein is one of the three macro-nutrients that provides the body with the calories it needs. Without eating foods rich in those three macro nutrients (protein, carbs, and fats), you should never expect to gain weight.
You can do this by eating calorie rich foods In general, such as foods rich with carbohydrates and fats beside protein rich foods as I mentioned above.
Carbohydrates will help you get energy and will also help you to gain weight. Foods that are rich with carbohydrates are grains, such as pasta, rice and oats. Fruits and some vegetables, such as potatoes also have calories, so you should eat regularly.
Fats also will give you calories. A gram of fats contains 9 calories. It’s more than what you get from protein and carbohydrates foods, with 4 calories per gram of each.
Just make sure that you eat them on daily basis, and you can gain weight.