Myth 7: Fasting Slows Your Metabolism
Another common misconception is intermittent fasting negatively impacts your metabolism over time. However, research indicates short-term fasting of 24-48 hours actually boosts resting metabolic rate up to 14%.
The body will not be affected just because you skip a meal. The body will switch to economy mode at the earliest when you haven’t eaten anything at all for at least 60 hours (source). By lowering the metabolism, the body uses the available fat reserves.
But now it gets really interesting: Before the body falls into the economy mode, metabolism increases again. It can then become up to 14% faster (source, source).
The catecholamines epinephrine and norepinephrine are increased during fasts, stimulating greater energy expenditure. The metabolic rate starts to decline only after several days of fasting as the body aims to conserve energy. But intermittent daily fasting does the opposite.
Refeeding periods after fasting also increase metabolic rate via the thermic effect of food. So intermittent fasting may create “metabolic cycling” where metabolism ramps up during the fasting state and feeding state due to changes in hormones.
Rather than slowing metabolism, studies show intermittent fasting causes a metabolic shift towards fat-burning without reducing total daily energy expenditure compared to regular eating patterns.
