The three most common fears about fasting — losing muscle, entering starvation mode, damaging metabolism — each get the timescale wrong. During a short fast, growth hormone rises measurably, resting energy expenditure does not fall, and the body burns stored fat. Two qualifiers belong with that reassurance rather than after it: past roughly sixty hours the metabolic picture changes, and the measured rise in expenditure was smaller in the larger trial and did not reach significance in men. What survives both is the answer to the fear — short fasting does not slow your metabolism down.
This companion examines each fear, what the research shows and where it stops, and the common thread of confusing brief fasting with chronic starvation. (6 min read)
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