Intermittent fasting is not a diet, but a pattern of eating. It can help you lose weight, but it remains dependent of the fundamentals of Body Re-composition. In other words, calories in vs calories out. However, other than being very useful for body re-composition, Intermittent Fasting can help you keep better control of your calorie intake. It also offers a multitude of benefits, from boosting the immune system, to stimulating brain function. How does it work? Well, your body has only two states of being when it comes to your metabolism: a Fasted state and a Fed state. In a Fasted state, Insulin is low, while glucagon and growth hormone are high.
Glucagon is produced by the pancreas and it is the main catabolic (breaking down) hormone of the body. Glucagon also decreases fatty acid synthesis in adipose tissue and the liver, as well as promoting lipolysis in these tissues, which causes them to release fatty acids into circulation where they can be catabolized to generate energy in tissues such as skeletal muscle when required. Basically Glucagon:
In other words when you are in a fasted state you are essentially in fat burning mode.
The opposite is true when you are in a Fed state. Once Macros enter your system, even in the smallest amount, your metabolism changes completely. It immediately moves into an Anabolic state (building/storing).
Glucagon production stops and Insulin production starts. Fat burning stops. Muscle building (or fat storing) starts. Whether you are repairing or building muscle or storing fat will be highly dependent on your activity level and your training protocol, and the timing of it. If, when in a fed state, you consume more calories than you burn, well, you will still gain fat, even if you use Intermittent fasting.
There are many ways to use Intermittent fasting, from once weekly for 24 hrs or on a daily basis for shorter periods of time. Since this is a Strength Training and Body Re-composition website, I will not dwell on all aspects and possibilities of using Intermittent Fasting. More on this in Intermittent Fasting 102.