is there any natural diet to gain mass

You should try a varied diet. Many people suggest that by eating a lot of proteins (meat, eggs, nuts, beans) your muscles grow bigger. In fact, this should be combined with a similar intake of vitamins (fresh fruit and vegetable), which facilitate the metabolism of proteins, plus carbohydrates, providing the necessary amount of energy, to keep those muscles active. Calculate the daily quantities for all the above food ingredients and by the consumption of the right quantities on a different menu every week, you can rest sure, that in no time you 'll obtain the required results. An important note: Don't forget aerobic exercise, since it plays a great part in gaining muscle mass, along with weightlifting exercises.