In 2012, a think tank called the Copenhagen Consensus Center convened some of the world’s leading economists and development specialists to ponder a question: If they had an extra $75 billion to improve the state of the world, which problem would they solve first? The group declared that investments to eliminate hunger and malnutrition would do the world the greatest good. It found that improving child nutrition was also the most cost-effective intervention, with a return on investment of at least 30 to 1, depending on the country involved.

The Lancet, meanwhile, has published a series of articles that refine the target of those investments, zeroing in on the benefits of maternal and infant nutrition, particularly during the 1,000 days. The British medical journal estimated that 165 million children in the world suffer from stunted growth due to malnourishment, resulting in “compromised cognitive development and physical capabilities, making yet another generation less productive than they would otherwise be.” Since stunted children become stunted adults, The Lancet concluded, “Countries will not be able to break out of poverty and sustain economic advances without ensuring that their populations are adequately nourished.”

The consequences of stunting in the 1,000 days spread outward, from the individual (less education, lower earnings), to the family (one less full-wage earner), to the community (a diminished labor pool), to the nation (lower economic activity and growth), to the entire world (weaker global trade). Nations with high child-stunting rates—in more than 40 countries, at least 30 percent of children under five are stunted—calculate that they annually lose as much as 5 to 17 percent of their GDP due to lost productivity, reduced schooling, and high health costs, all of which stem from stunting that begins in the 1,000 days. In essence, malnutrition keeps poor countries poor.

Ethiopia, which has been plagued by a series of hunger crises over the past several decades, estimated in a recent report that two-thirds of its adult population suffered from stunting as children. According to the study’s calculations, in 2009—25 years after the epic famine of 1984, when nearly 1 million people died of hunger—the cumulative impact of malnutrition on education levels and workplace productivity cost the country the equivalent of 16.5 percent of its GDP, or about $4.7 billion.

For me, the human face of these numbers is a boy I first met during the Ethiopian famine of 2003, when international food aid was keeping 14 million people alive. Hagirso was five years old and weighed just 27 pounds when his father, Tesfaye Ketema, carried him into an emergency feeding tent. Tesfaye explained that his son, who was sickly and weak and stunted, had been malnourished since birth and was the most vulnerable in the family when the famine hit. Hagirso miraculously survived, but his early malnourishment and the subsequent famine exacted a tremendous toll. When I visited him 10 years later, in April 2013, Hagirso was 15 and barely four feet tall. Tesfaye said his son was often sick and wasn’t strong enough to do much work on the small family farm. Hagirso was in school, but only in the first grade. The day I visited, he and his much-younger classmates were studying the alphabet and pronouncing vowel-consonant combinations: ba, be, bi, bo, bu. There, in that classroom, was confirmation of all the statistics on the cost of malnutrition and stunting: lost education, lost work, lost wages, lost opportunity.