Losing weight is a matter of calories. You can't eat or drink more than you burn and lose weight. It takes approximately 3,500 calories to gain or lose one pound of fat.  To lose about one pound per week, you could eat 250 calories less per day and do extra activities to burn 250 calories per day. How ever each persons body is unique.  See how your body responds after several weeks of eating less and/or being more active.  A safe rate of weight loss is 1/2 pound to 2 pounds per week.