In this post, I introduce key hormones that directly or indirectly affect fat burning. This article is not about weight loss, but it is about fat loss. The difference is people may lose weight by losing fluid, glycogen, muscle, and even bone density. However, of course, no one wants to lose valuable muscle and critical bone density for the sake of losing weight. Thus, my focus is losing fat, more precisely, using fat as energy for sustainable vitality, fitness, and health.