You don't gain 100 pounds quickly. But pregnancies, a slowing metabolism and poor eating habits can slowly pile on those extra pounds. Just as you didn't gain the weight overnight, you shouldn't expect to lose it quickly, either. But if you're patient and committed, you can lose 100 pounds without resorting to pills or surgery. The secret is simple: good old-fashioned diet and exercise. Aim to lose 10 percent of your body weight in six months and reevaluate your weight-loss goals after meeting this target.
Set an initial goal of losing 10 percent of your body weight over a six-month period as recommended by the National Heart, Lung and Blood Institute's "Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults." For instance, if you weigh 260 pounds, your initial goal should be to lose 26 pounds in six months -- or one pound per week.
Add exercise to your routine. According to the NHLBI, you should start with a simple plan of walking for 30 minutes three days a week, for a total of 90 minutes per week. Build up to 45 minutes of walking five days per week, for a weekly total of 225 minutes. Walk your children to school instead of driving them to get your exercise and set a good example. If you have young kids, take them in a stroller so you don't need to find a sitter while you exercise.
Create a calorie deficit by reducing your calorie intake in addition to burning calories from exercise. One pound of fat is equal to 3,500 calories, so you can find your daily calorie deficit goal by multiplying your weekly weight-loss goal by 3,500 and dividing by seven. For instance, a weekly weight-loss goal of one pound is equal to a daily deficit of 500 calories.
Reevaluate your weight-loss goals after six months. For instance, if you initially weighed 260 pounds and you lost 10 percent of your weight, you would still need to lose 74 pounds to achieve your goal of losing 100 pounds.
Continue increasing your exercise. According to the American College of Sports Medicine, you'll need to exceed 250 minutes per week to see clinically significant weight loss. In addition to walking, add other simple family activities, such as playing soccer with your kids or going on hikes.
Create a new calorie deficit to lose the additional weight. According to the NHLBI, it's safe to aim for weight loss of between one and two pounds per week. This is equal to a daily deficit of 500 to 1,000 calories. Keep in mind that you calorie deficit comes from both increased activity and a reduction in your calorie intake.