Ask anyone how to lose weight and they will tell you to eat less. If you eat less calories than you burn you will lose weight. While this is true, there is a point where you can eat so little, you will cause your metabolism to slow and not lose anymore weight.
Healthy Weight Loss
Healthy weight loss is 1-2 pounds per week. To lose one pound, you need to create a calorie deficit of 3,500 calories. You can spread this 3,500 calorie deficit over a week to lose one pound per week (create a deficit of 500 calories per day). If you want to lose two pounds per week, double the deficit to 7,000 calories per week or 1,000 per day.
Too Much Too Soon
The problem people run in to is trying to lose too much weight too quickly. If you try to lose more than 2 pounds per week, your daily deficit will be greater than 1,000 calories per day. This will require you to drastically cut your calorie intake which could cause your body to think you are out of food and starving. To conserve energy, it will start slowing down a lot of processes to decrease your energy expenditure; it will burn less calories.
The result of this slowed metabolism is you will lose less weight than you were planning on. Try not to eat under 1,200 calories per day as this is what your body considers starvation territory. If you subtract 1,000 calories from what you burn and get a number under 1,200, exercise to burn more calories instead of cutting them out of your diet. Find out how many calories you burn each day using the Calorie Calculator.