According to existing recommendations of the Food and Agriculture Organization (FAO)/World Health Organization (WHO), the amount of provitamin A in a mixed diet having the same vitamin A activity as 1 ?g of retinol is 6 ?g of ß-carotene or 12 ?g of other provitamin A carotenoids. The efficiency of this conversion is referred to as bioefficacy. Recently, using data from healthy people in developed countries and based on a two-step process, the U.S. Institute of Medicine (IOM) derived new conversion factors. The first step established the bioefficacy of ß-carotene in oil at 2 ?g having the same vitamin A activity as 1 ?g of retinol; the second step established the bioavailability of ß-carotene in foods relative to that of ß-carotene in oil at 1:6. Thus, 2 ?g of ß-carotene in oil or 12 ?g of ß-carotene in mixed foods has the same vitamin A activity as 1 ?g of retinol. Based on existing FAO food balance sheets and the FAO/WHO conversion rates, all populations should be able to meet their vitamin A requirements from existing dietary sources. However, using the new IOM conversion rates, populations in developing countries could not achieve adequacy. Additionally, field studies suggest that, instead of 12 ?g, 21 ?g of ß-carotene has the same vitamin A activity as 1 ?g of retinol, which implies that effective vitamin A intake is even lower. Therefore, controlling vitamin A deficiency in developing countries requires not only vitamin A supplementation but also food-based approaches, including food fortification, and possibly the introduction of new strains of plants with enhanced vitamin A activity.