Adrenalin Fasting increases adrenalin levels, starting at around twenty-four hours. Forty-eight hours of fasting produces a 3.6 percent increase in metabolic rate,15 not the dreaded metabolic shutdown so often seen in caloric-reduction strategies. In response to a four-day fast,16 resting energy expenditure increased up to 14 percent. Rather than slowing metabolism, the body revs it up instead. Presumably, it does this so we have energy to go out and find more food.
