Why short-term fasting doesn't slow your metabolism like chronic dieting does.
What the evidence says
- Contrary to popular belief, short-term fasting does not decrease metabolic rate1,2
- Studies show resting energy expenditure may increase by up to ~14%1,2
- This differs from chronic calorie restriction, which can reduce metabolic rate3
- Norepinephrine more than doubles during short-term fasting (1716 → 3728 pmol/L over 84 hours)1
- Norepinephrine signals fat cells to release fatty acids (lipolysis)2
- The hormonal environment (high norepinephrine, high GH) explains the difference1,4
- Extended fasting (60+ hours) does reduce metabolic rate — 24h energy expenditure dropped ~11% in 60-hour fast5
- Intermittent fasting (cycling short fasts) avoids the metabolic adaptation of chronic restriction while allowing fat access1,6