At this time of the year everyone is a nutrition expert. All it takes is for someone to have a little bit of success following a certain food plan and this is then preached to the world.
Be careful who you are getting your advice from. Unless is is from a registered dietician, you should be taking it only as advice and then weighing up whether or not it may work for you.
Hint - not everything works for everyone... The way your friend lost weight might not work for you.
One popular form of dieting is the 5:2 diet - eating pretty much what you want for 5 days (within a calorie goal) followed by 2 days of 'fasting', consuming around 500-600 calories.
Now the problem here is that it doesn't influence your eating habits positively (possibly encouraging binging episodes). This mainly due to eating whatever you like for 5 days - cakes, chocolate, whatever as long as your in your calorie goal. There is no focus on making a slow change to healthy nutritious food sources.
Introducing two days of fasting/starving yourself then has the potential to create binge tendencies - your body has been 2 days without a proper intake of food. Once you start eating again, its going to want you to get as much as you can in.
If a food plan or diet tells you to massively restrict your calories for a set period of time and promises you whatever you want for the rest of the time, question it, and If you already have a tendency to binge, it's probably not for you.