Undernutrition increases susceptibility to illness and risk of death and contributes to neurocognitive development delays, reduced school achievement, reduced earnings in adulthood, and increased probability of chronic diseases. Current evidence demonstrates that the most effective strategy to reduce stunting is through programs that prevent rather than treat linear growth retardation in the first 1,000 days. Authors argue that early undernutrition has irreversible impacts and cautions against studies suggesting otherwise.