The amount of time required to lose 10 pounds with an intake of 700 calories a day will vary greatly depending on level of daily activity, age, sex, height, starting weight and other prior health factors. For example, the average healthy female who is moderately active and is between the ages of 20 and 30 will lose 10 pounds in approximately 23 days (based on an average BMR of 1,300), but this time frame may be drastically different for a man who is more active or an older woman in her 40s who lives a very sedentary lifestyle.
When a person quickly and suddenly decreases daily caloric intake, the majority of the weight lost within the first several days is water weight. The most accurate way to determine a time frame for weight loss is to calculate the BMR, basal metabolic rate. This rate refers to the amount of calories a body burns daily without any extra exercise.
Once the BMR is determined, the amount of calories burned through daily physical activity should be calculated and added to the BMR. The result is the total number of calories burned per day. The number of calories consumed can be subtracted from the total of calories burned, resulting in net calories. It takes a deficit of approximately 3,500 calories to burn 1 pound. Once the net calories for a number of days equals 35,000 calories, theoretically, 10 pounds would be lost.