Metabolic rate is how much energy (calories) your body uses in a day for normal function. This is the energy for your brain, heart, liver etc. and does not include exercise. We know that calorie restricted diets lower metabolic rate, and this limits weight loss, and is often called starvation mode. Dr. Jason Fung explains why fasting does not lower metabolic rate thus allowing you to avoid the dreaded starvation mode that leads to weight loss plateau.