Is there something special about exactly 0 calories vs 1 calorie?
When researching Intermittent Fasting, the "magic" seems to come from the body's response to insulin dropping and its response to secrete glucagon, causing glyconeolysis, catabolism, gluconeogenesis, and lipolysis - the latter three becomes dominant once the liver runs out of glycogen.
One thing that's mentioned several times by online articles and books (such as The Obesity Code) is that "reduced calorie" diets do not cause the same effects. However, they rarely go into what effects specifically they're talking about, or how reduced is "reduced."
If you are fasting at 0 calories, does the addition of one calorie somehow cause the glycogen to stop causing the lipolysis, gluconeogenesis, and catabolism? What about 100 calories? 500 calories?
What happens in the transitional region between 0 calories ("fasting") and 1500 calories ("reduced calories")? If you're fasting for 16 hours, eat 100 calories, then fast 16 more, how significantly different is that from fasting 32 hours?