If i am 50 pounds overweight is it safe to lose 4 pounds a week?

Actually: it's next to impossible. That would require burning off 14,000 calories that you don't eat. If you ate nothing and walked every day, you would have to walk 140 miles each week to lose that amount of weight. Why not try a safer and slower approach to improve your diet and exercise with a plan you can live with for the rest of your life. Don't listen to friends, tv or internet scams.