A study of four consecutive days of fasting—that is, four full days without any food to eat—showed that BMR increases by about 10 percent. Yes, metabolic rate increases when you don’t eat. Why? We know that fasting decreases insulin but increases counter-regulatory hormones, so called because they run counter to insulin. If insulin falls, these hormones go up. If insulin rises, these hormones go down. The counter-regulatory hormones include noradrenaline (responsible for stimulating muscle contraction and heart rate), growth hormone (stimulates cell growth and regeneration), and cortisol (the
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