Dr. David Sinclair tries to fast for 3 days once a month because a type of cellular recycling called chaperone-mediated autophagy, a deep clean of old and damaged proteins, only happens after 2.5 to 3 days.

“The claim accurately reflects statements made by Dr. David Sinclair, who has said that extending a fast to three days triggers an advanced form of cellular cleaning called chaperone-mediated autophagy (CMA). However, the scientific premise that CMA *only* happens after 2.5 to 3 days is an oversimplification. Research indicates that while general autophagy peaks around 48-72 hours, CMA is initiated much earlier—after about 10-12 hours of fasting—and reaches maximal activation around 36 hours, a level which is then sustained. Context: The claim presents Dr. Sinclair's stated reason for a prolonged fast. While he has linked the 3-day mark to CMA, scientific sources suggest this specific process begins much earlier and peaks around day 1.5 to 3, rather than only starting at the end of that period.”