To lose weight you need a calorie deficit. A calorie deficit that’s too large or maintained for too long, will eventually invoke the starvation response and slow your metabolism. The goal is to use a small deficit and avoid diets that call for extremely large calorie reductions.

Calories are the most important factor in weight loss. If you are eating more calories than you burn, you will not lose fat, no matter what.but if you create just the right deficit with the right nutrition and exercise then your body has to use stored energy for fuel. And fat is nothing more than stored energy waiting to be releases when it is needed.

As I mentioned before cutting calories too much can have negative effects. so the question is how low can you go without negative effects? The most common guideline for fat loss is to reduce your calories by at least 500, but not more than 1000 below your maintenance level. The guideline for recommended safe calorie levels is a 1200-per-day-minimum for women and 1800-per-day-minimum for men. so a 1000 calorie deficit can be too much for some people.

A more precise way to determine your correct calorie deficit would be to use a percentage deficit relative to your maintenance level. Reducing calories by 15-20% below maintenance level work for most people. A larger deficit (25-30%) might be necessary for some people, but it is always better to burn more calories with exercise then to reduce with diets. The larger of a deficit you create, the sooner your body will catch on that you are dieting and the sooner it will start slowing your rate of calorie burning.