Atmospheric CO2 is on pace to surpass 550 ppm in the next 30-80 years. Many food crops grown under 550 ppm have protein, iron and zinc contents that are reduced by 3-17% compared with current conditions. We analysed the impact of elevated CO2 concentrations on the sufficiency of dietary intake of iron, zinc and protein for the populations of 151 countries using a model of per-capita food availability stratified by age and sex, assuming constant diets and excluding other climate impacts on food production. We estimate that elevated CO2 could cause an additional 175 million people to be zinc deficient and an additional 122 million people to be protein deficient (assuming 2050 population and CO2 projections). For iron, 1.4 billion women of childbearing age and children under 5 are in countries with greater than 20% anaemia prevalence and would lose >4% of dietary iron. Regions at highest risk—South and Southeast Asia, Africa, and the Middle East—require extra precautions to sustain an already tenuous advance towards improved public health.