An extensive literature documents linkages between early nutritional deficiencies and reduced cognitive ability, educational attainment and, ultimately, lower labor market performance. Few of these studies, however, have shown these correlations to be genuinely causal. We reexamine the nutrition and cognition link, applying instrumental variable methods to a sibling-difference specification for a sample of Peruvian pre-school children. We use household shocks and food price changes as instruments. As such our analysis also quantifies the nutritional and cognitive costs of the 2006-08 global food price crisis. We find that there are significant and negative cognitive effects of early childhood nutritional disinvestments: a decrease in Height-for-Age z-score leads to a reduction in the Peabody Picture Vocabulary Test score of 17-21 percent. The accumulated deficits are sizeable considering that these children are only 3-6 years old and are yet to enroll in formal schooling, with deficits likely to widen in later years.