To lose bodyfat, you need to create a calorie deficit. But, this is not the whole story...
Suppose your body needs 2500 Kcal per day to stay at the same weight.
When you start eating 500 Kcal less per day, your body will "know" after a while that you are eating not enough to maintain your metabolism and it puts itself in "starvation mode": your metabolism will slow down and your body needs not 2500 Kcal per day anymore, but less.
After a while, you notice that your weight isn't dropping anymore and you start eating 500 Kcal less per day (your calorie intake is now 1500 Kcal/day). Your metabolism slows down further and eventually, when you have starved yourself, you decide that this cannot go on and you start eating the same amount of calories as before.
As your metabolism is very slow now, your body isn't capable to process 2500 Kcal per day and it stores the excess as bodyfat.
This is the well-known yo-yo effect. Most people who followed a diet know what this it.
How to avoid this...
- Eat the same amount of calories as usual and start MOVING!
Instead of eating 500 Kcal less per day, burn these 500 Kcal in your muscles (cardio!)
- Spread your calories over more meals per day.
- Start weight training: the more muscles you have, the more calories your body burns
If you eat less calories per day, change your routine after a few days:
For example: 3 days less calories, then a day with normal (or even MORE) calories (like before your diet), 3 days less calories, another "normal" day, etc.
This way, your body won't go in starvation mode because it knows that plenty of food is coming after a while.