Achieving food security while limiting environmental degradation is a central challenge for Africa's rapidly growing population and agricultural systems. We develop a national-scale nitrogen (N) budget framework for 54 African countries and project N flows to 2050 under four scenarios: Business as Usual (BAU), a 20% reduction in reactive N losses (BAU-20 L), dietary self-sufficiency through agricultural intensification (SDT), and a sustainable pathway that combines loss reduction with balanced nutrition (BDT). Monte Carlo simulation (10,000 iterations) quantifies trade-offs among crop production, N use efficiency, and reactive N losses. From a current mean N input of 63 kg N ha-1 yr-1, BAU maintains protein deficits: only nine countries meet the dietary adequacy threshold (>= 4 kg N cap-1 yr-1), including five in North Africa, while total N input rises to 98 kg N ha-1 yr-1 by 2050. BAU-20 L lowers reactive N losses but does not close yield gaps. SDT improves food security, yet it raises N surpluses in some countries while soil N mining persists in nutrient-limited systems. BDT reaches food security by 2050 at the current N input rate, supported by a larger contribution from manure recycling and biological N fixation (BNF). Eliminating soil N mining under BDT would require 151 kg N ha-1 yr-1 of total N input, with 58% supplied by manure and BNF. Overall, sustainable N intensification in Africa calls for higher N supply and a rebalancing toward organic and biological sources, enabled by improved nutrient management.