Fasting is a technique I've employed many times for spiritual focus and gain, but never for health or weight loss reasons. In order to really understand why fasting doesn't help you lose weight, at least not in a sustainable way, I have to introduce a few biochemistry terms to you. I hope your eyes haven't already glazed over. If you're anything like me, you don't just want advice, you want to know why and how things are the way they are, that way you don't have to just memorize, you can understand.
The two characters in our story are two hormones. The first is one you've probably heard of: insulin. Insulin is created by the pancreas every time you eat carbohydrates (sugar, starch, etc.) and it regulates the amount of those carbs in your blood. Insulin does many things, but the most important thing it does is create fat, which is your body's way of storing energy. Without insulin, there is no fat creation. Basically under normal circumstances, the more full you get, the less you want to eat.
Our second character is leptin. Leptin is the hormone that tells your brain to tell your body to burn energy. Your body stores energy as fat, so basically leptin is the hormone that tells your body to burn fat. As leptin rises, it tells your brain that you have plenty of energy (fat) and that your brain should feel free to have your body burn that fat. Conversely, when leptin levels are low, your brain thinks you are starving, and it instead tells your body to conserve energy (create fat). Still with me?
Here is what all this means for you when you fast. When you engage in a short term fast, leptin levels drop rapidly (within 12 hours), declining much faster than your body's stores of fat. That drop in leptin signals to your brain that you are starving and it needs to go into energy conservation mode, so your brain will tell your body to conserve energy and hold onto every calorie it has. Your body stores those calories as fat for the coming famine your brain thinks you are about to go through. This is why nutritionists will tell you not to skip meals. You want leptin in its proper balance so your brain doesn't take your body into famine mode.
I will talk more about insulin and leptin going forward, as they are the key ingredients in our biochemistry that affect our weight loss and weight gain. When I give advice, I want you to do it in a way that allows you to understand your body better. Because ultimately, understanding and being in tune with your body will be the key to your living a healthy life far into the future.