Intermittent Fasting vs. Calorie Restriction
There is some confusion between “low-calorie diets” and fasting protocols. Some low-calorie diet research shows harmful effects of damaged metabolism which can slow down long term and revert weight loss results in many people. 
Fasting does not necessary restrict calories but, the times the food is consumed. Furthermore, such protocols have been shown to enhance metabolic activity in both men and women. [4,10]
Yes, intermittent fasting can inherently reduce calories, but that is not the goal of these protocols. Meals during an eating window should make you full and satisfied.
Fasting boosts metabolism by adjusting key hormones (low insulin and higher norepinephrine) that revs up energy production. During a fast, the body taps more into stored fat (due to dwindling glycogen levels) for all the metabolic needs.
The longer the fast the more stored fat is utilized for sustainable energy. This method increases metabolism (up to 13%) producing plenty of steady energy. 
Enhanced Mitochondria Activity
Another big topic is the energy production within the cell itself and the power-plant organelle called mitochondrion.
Mitochondria are where majority of energy produced by braking down fat and sugar stores while using oxygen.
Different cell types vary in mitochondria quantity. For instance, muscle cell has more mitochondria than skin cell.
Fasting studies show mitochondria within cells link up into a network and work together becoming more efficient in generating more energy for longer. 
Intermittent Fasting: Keep Muscle & Lose Fat
IF is a powerful weight loss tool, as overwhelming majority of research shows significant results in humans and animals.  The body uses metabolic hormones (low insulin) to tap into its energy stores; first using glycogen followed by stored body fat. 
Bonus: the fat we burn during fasting is harmful visceral kind (stored around the belly and internal organs) that increases risk for many metabolic diseases. [13-14]
Another big benefit of IF weight loss is longevity, as more people are able to take the weight off and keep it off. The body uses fat stores for energy while maintaining lean mass. 
Muscle tissue isn’t burned during fasting but remains intact and active. This includes reconfiguring of another metabolic hormone called human growth hormone (HGH).
Fasting increases HGH levels as much as 5-fold, further reducing waistline size while maintaining muscle and bone.  And, exercise of all levels during fasting maintains lean mass while accelerating fat burn as fuel. [4,14-15]
Personal Experience: Both Victor and Dupi strength and power train in a fasted state. On average Victor eats 6+ hours later and Dupi 3+ hours after a workout. Feel free to visit our IG profiles to see results. @godupigo @victory.rising