For people with stable weight to lose 100 pounds in three months, they must create a deficit of 3,684 calories per day through diet and exercise, explains WebMD. Eliminating 3,684 calories a day in food alone is possible for a person who typically eats more than 4,634 calories per day.
The lowest recommended caloric intake is 1,050 calories, and eating less than this amount can be dangerous, warns WebMD. Weight loss as rapid as the 7.5 pounds per week needed for 100 pounds in three months is considered unusual and unsafe by most health professionals under most circumstances. Cutting calories by eliminating specific foods, such as salts and starches, may speed up weight loss at the beginning, but because the weight lost from this strategy is usually water weight, its effectiveness is limited over longer periods.
Long-term diets limit these foods as well as animal fats while reducing overall calorie consumption, but dieting alone is less effective than combining diet and exercise to create the necessary caloric deficit. Working out moderately for an hour each day burns the extra calories needed for faster weight loss. Moderate exercise means breaking and maintaining a sweat throughout the workout, which can be achieved by a cardio warm-up followed by light weight training that gets the body moving and builds lean, toned muscle.