Diet and exercise should form about 80% and 20% respectively of your weight loss efforts. However, you can lose up to 8 pounds in 3 weeks without performing exercise. There is only one way that you can lose weight if you are deciding not to take up any specific exercise workout routine. Yes, you can do it by only creating a calorie deficit. Your body needs certain amount of calories to carry out various functions and the amount of calories vary depending upon your body type and the level of fitness.
There are commercial weight loss programs like Nutrisytem, Jenni Craig and Medifast that offer safe weight loss of up to 2 lbs per week. Nutrisystem does not ask any doctor recommendation to follow their diet plans and it is open for all. Both Jenny Craig and Meidfast require recommendation from doctors as they offer low calorie diet foods which offer quick weight loss. Jenny Craig provides around 80 meal choices and most of them are frozen varieties. Nutrisystem offers over 150 meal choices which include both shelf stable and frozen varieties. You can read this comparison article to understand the diet planners in a better way.
When you do not consume the required calories for the day, the body tries to draw energy from the stored fat. Likewise, when you consume too many calories than required it leads to fat storage all over the body. Eating below the caloric requirement surely leads to weight loss but it completely depends on how fit you are physically now. As consuming less calories than the daily requirement leads to drop in energy levels and nutrition deficiency, it is important that you determine your current calorie requirement using a calorie calculator. Going on a starvation mode is dangerous; women should consume 1200 calories per day and men about 1800 calories to carry out the daily activities.