My friend told me a protein diet is the best and easiest way to lose weight fast, is this true?

Yes: Following a low carb high protein ketogenic diet is a safe way to lose weight fairly rapidly. Basically have 2-4 oz of protein with each meal, no starch or sugar (only green veggies and berries and melons) as your source of carb and plant and fish based fat and your should be able to lose the weight. For exercise best is spinning and circuit training.