4lbs a week is alot, sometimes you loose more at first b/c your new ways of eating and exercise are like a shock to your system, but then it slows down to 1-2lbs a week and thats the best way to go.
to loose 1lb a week you need to have a calorie deficit of 3500(a week) works out to 500 cals a day-so lets say your daily intake is 2000 cals/a day, you would want to create a defict by exercise or reducing cals ex: eat 1800 cals a day and burn 300 cals a day w/ exercise then you would get your 1lb weight loss for your week , hope this helps (and yeah errtu's pretty darn helpful and full of advice, just make sure you always tell him you get more than 1700 cals in a day lol)