Hello, thanks for the query.
There are so many myth in India as this is one of them.
Gym give a shape to your body + peace of mind+ stamina required + good look + physic.
Only one loss is there that is of money.
Don't bother about, what others say.
When you do exercise with full heart and zeal, this give you peace of mind and joy.
Regular exercise are necessary for today's life.
During GYM if very hard there is burn of extra carbohydrate
( sugar) , dissolve fat if extra, utilize protein which gives shape to your muscles.
Good luck and keep it up . Dr. HET.