One of the first things that you'll do when you decide to lose weight is to set a goal weight. For most, that goal will be their 'ideal weight', but for many, that 'ideal weight' may be exactly the wrong weight for them to be aiming for.
Years of dieting or being overweight have the physiological effect of moving the body's concept of the 'ideal weight' from what is truly considered ideal. The 'set point' is the weight at which your body naturally feels most comfortable.
If you've been overweight for a very long time, or if you've consistently 'yo-yoed', your body may respond to your initial weight loss by lowering its metabolism because it believes that you are starving to death. This slowing leads to discouraging plateaus that often knock people off their diets entirely, and lead to regaining all or part of the lost weight.
Instead of aiming for an 'ideal weight' that calls for you to lose weight steadily for months or even years, many experts recommend aiming for shorter-term attainable goals. Since the bulk of diet research shows that most dieters lose weight steadily for about 12 weeks, then hit a plateau, that's the number that they suggest you aim for. The strategy that many have found works best for them is one of alternating periods of weight loss and maintenance, each lasting 8-12 weeks.
Choose a realistic amount of weight that you can lose in 8-12 weeks. Figuring that the most reasonable and healthiest weight loss rate is 1-2 pounds per week, 30 pounds in three months is not unreasonable. Diets until you reach that goal, or for 12 weeks, whichever comes first, and then switch to a maintenance diet.
Why switch to a maintenance diet at that point? In part, you're giving yourself a 'breather', a break from more restrictive eating. The other part, though, is that you're re-educating your body and letting it establish a new 'set point'. Once you've maintained your new weight for 8-12 weeks, set another weight loss goal, and move back into weight loss mode. By giving your body a break from 'starvation', you'll have overcome its resistance to losing more weight, and be back to dieting for 'the first two weeks' - the weeks that most people lose weight more rapidly.
You'll also be giving yourself a chance to 'practice' maintaining you're new, healthier weight. Researchers have found that more than half of the dieters who take off significant amounts of weight do not maintain that weight loss once they go 'off' their diet. By practicing weight maintenance in stages, you'll be proving to yourself that you CAN do it, and removing a powerful negative psychological block.
This will work with any long-term healthy weight loss diet, no matter the focus. You'll find it much easier to do if you choose a diet that has concrete 'phases', like the South Beach or the Atkins, since the weight loss and maintenance phases are clearly laid out for you to follow. Regardless of the diet you choose, though, by alternating between weight loss phases and maintenance phases, you'll teach yourself and your body how to maintain a healthy weight.