diet : you are what you eat

A friend of mine was asking me about what kind of diet she should have had. For information, she only weight about 45 kgs ( = 100 pounds ) with 1,60 height. In my calculation her BMI or Body Mass Index is around 17. Which you could say she's thin. But she said that she want to lose another 3 kgs if she can.
The normal Body Mass Index should be around 18-25, you could get your BMI in this way :

BW / ( HxH )
BW : Body Weight (in kgs) , H : height (in meter).

Contrary to the story I have mentioned, I have another friend who get overweight by her eating habit. She have gone through many diets for losing her weight, and it only lasted for a while, until she backed to her old eating habit.


I really think that instead of being victim of many kinds of diet style ( for example, I named few of them : South beach diet, Blood type diet, Food combining diet )
it is more important to know what kind of diet who suits with one's eating habit.
To get it clear, if you get used to with taking breakfast in a medium portion, do not try to eliminate your daily habit at once. But, instead of taking high calories intake as a breakfast, you could switch to a healthier meal or even replace it with fruits like banana or apple.