Anecdotally fasting and calorie restriction seems to give me short-term energy in exchange for the long-term need to replenish the energy. After several hours w

Anecdotally fasting and calorie restriction seems to give me short-term energy in exchange for the long-term need to replenish the energy. After several hours without eating i feel really good, even doing intense exercise. I continue to feel good and energetic sometimes even after a full day. But fasting too long or losing too much weight and I start getting really tired. And then when I eat it makes me even more tired because eating in general makes me kind of lethargic.