What is intermittent fasting?  Also know as IF. This is a health trend and not a diet. Do not confuse it to any diet program because it is totally different. You are not starving yourself but in fact fasting.  This is when you only eat within a certain window frame. We have been doing this all our life; when we sleep our body is in fasting mode. This is nothing new, probably just the term.
This can help with health and calorie-control benefits. This is not a water fast or dry fast. You still need to eat.
You have different fasting windows which are as follows: 16:8, 18:6, 20:4, fast for three days and eat regularly the others days, fast for two days and eat regular the other days. What does this mean? For example. 16:8, you will fast for 16 hours and eat within the 8 hour window or fast for 18 hours and eat within the six hour window and so fort.  The other way is to alternate days.
What is allowed when fasting:  During fasting you cannot have any calories. You are not allowed black coffee, black tea, green tea, unflavored water, unflavored carbonated water and unsweetened electrolytes. This would be considered part of the clean fasting.
Remember that if you are doing this consistently, it will then become the norm. Our body is equip to handle long periods of not eating. Your body will fall into a routine just like you train a child.