Tried a 1200 calorie diet? ( Archived) (65)

Don't go much below ~1,600 calories. Less than that starts putting a lot of stress on the body.

Don't cut down calories suddenly. This will trigger a stress response where the body will go into starvation mode and start saving as much as possible. Go down gradually.

Don't diet for long. Cycle with going back to maintenance levels (and even above, if you're exercising) for a while, then slowly cut down again. As said before, avoid the sudden stressful changes. Don't be afraid of having one cheat meal a week so that your body remembers what it's like to have good supply of calories - avoid the stress response of starvation!

Do high intensity interval training, not long steady slow cardio. Long steady cardio will eat up at your muscle when glycogen stores run out (this is not something up for discussion, Pyruvate decarboxylation is an irreversible step in our metabolism, so if you burn all your sugar you WILL go into gluconeogenesis and start breaking down protein - muscle; that's bad). Long cardio has also the downside of slowing down your metabolism as the body becomes more efficient at doing it, so as it's been kindly pointed out, vary it a bit. Sprints, elliptic, rowing, cross-training, there are a million easy ways to do interval. Best way, you'll reap the benefit with as little as 20-30 minutes.

Don't be afraid of doing weight lifting exercises - real free weights, not machines. As a woman, you simply don't have the testosterone levels to get ripped or muscular without juicing, so don't worry about it. A firmer base of muscles will have the following benefits: Higher breasts (due to better support), perkier butt, and a higher base metabolism. Long term benefits include preventing osteoporosis, a good thing too.

Avoid processed carbs like the plague - go wholemeal. Distribute your carb intake along the day, so that you keep glycogen stores topped up and you don't burn the precious, high-metabolism muscle.

Most importantly, remember this is a permanent lifestyle change. One of the key reasons why all diets fail is the "I've lost the weight, I can go back to eating normal again" mentality. The previous normal is what got you there, so nip it at the bud. Good change on the diet and habits > quick fix of self-starvation to lose pounds faster. Take the weight off and KEEP IT OFF.

Good luck :)