Does fasting lower metabolism?

Fasting does not automatically lower metabolism, but its impact depends on the duration and how it is practiced.

Short-term fasting (12-24 hours):
In the short term, fasting typically does not slow metabolism. In fact, the body may slightly increase calorie burning due to the release of hormones like norepinephrine, which helps mobilize stored energy.

Intermittent fasting:
Common approaches like 16:8 fasting generally do not harm metabolism when total calorie and protein intake are adequate. Many people maintain or even improve metabolic health when fasting is combined with proper nutrition and exercise.

Long-term or extreme fasting:
Extended fasting or severe calorie restriction over several days or weeks can slow metabolism. The body adapts by reducing energy expenditure, lowering thyroid hormone levels, and conserving calories to survive.

Muscle loss factor:
If fasting leads to insufficient protein intake or lack of resistance training, muscle loss may occur. Since muscle supports metabolic rate, this can indirectly slow metabolism over time.

Key takeaway:
Fasting itself is not harmful to metabolism when done properly and for short durations. However, extreme or prolonged fasting without proper nutrition can reduce metabolic rate and negatively affect overall health.

To maintain metabolism while fasting, ensure adequate nutrition during eating periods, include protein-rich foods, and stay physically active.