So you want to lose 18 pounds in 4 days.
You cannot do this safely.
Unless you get rid of a leg, this is just not a realistic goal.
One of the problems I see so often with many different people that want to lose weight is that they set unrealistic goals then get frustrated when they don't reach them.
Now you can lose a lot of weight relatively quick with the right plan.
Fasting is not the right plan.
This is where you eat close to nothing at all and lose a lot of weight in a very short period of time.
This is not a safe way to get to the weight you want to be at and will cause you many problems in the long run.
You can easily lose 9 pounds every 11 days with the right plan so long as you stick to it.
One process that will help you achieve this is calorie shifting.
This is where you mix up the number of calories that you consume in a day but still stick to a specific amount for the week.
This will confuse the body and prevent it from stocking up on excess calories that you don't need.
Calories that just build up in case you need them later on.
They tend to accumulate in the mid section and are very hard to get rid of through "standard means".
If you really want to lose 18 pounds in 4 days then I will fist suggest you set an achievable goal with the right plan.