Which is the best supplement for lean person with workout when he want gain healthy muscle quickly.And I also like to know what will be the supplement intake routine. Height 5Ft 6Inch and Weight 50.5kg. Almost 10-15KG under weight
All the supplements in the world won't fix a bad diet. You're underweight because you're eating too little. You need to eat more. To put on lean mass, stick to having good macro proportions of protein, carbs and healthy fats, and eat at a caloric surplus.
And no, you do not have "fast metabolism" nor anything else. You just eat too little, and some pills won't make the difference to that.