Background:　Understanding　global　dietary　patterns　and　their　implications　for　human　and　planetary　health　has　become　increasingly　critical.　The　Planetary　Health　Diet　(PHD),　introduced　by　the　EAT-Lancet　Commission　in　2019,　offers　a　framework　to　address　nutrition-related　diseases　while　mitigating　environmental　impacts.　Objectives:　We　aimed　to　analyze　adherence　to　a　modified　PHD　(mPHD)　among　working-age　population　(WAP)　across　185　countries　between　1990　and　2018.　Methods:　We　conducted　a　serial　cross-sectional　analysis　using　data　from　the　Global　Dietary　Database　(GDD)　2018.　The　modified　Planetary　Health　Diet　Index　(mPHDI)　score　was　constructed　based　on　consumption　of　12　food　groups.　Each　component　was　scored　from　0　to　10,　generating　a　composite　score　ranging　from　0　to　120.　Distributive　inequalities　were　assessed　using　the　slope　index　of　inequality　and　concentration　index,　which　are　2　standard　metrics　of　absolute　and　relative　gradient　inequality.　Results:　Modest　overall　adherence　to　the　mPHD　recommendations　[global　mPHDI　score:　75.2;　95%　uncertainty　interval　(UI):　74.2,　76.3]　was　observed,　with　significant　regional　variations.　Sub-Saharan　Africa　showed　the　highest　adherence　(84.5;　95%　UI:　83.2,　85.5),　whereas　Latin　America　and　the　Caribbean　showed　the　lowest　(66.0;　95%　UI:　64.5,　67.7).　Excessive　consumption　of　red/processed　meat　and　added　sugar　was　prevalent　across　various　populations.　Over　the　past　28　y,　global　improvement　was　minimal　(+1.3;　95%　UI:-0.1,　2.4),　with　concerning　declines　in　South　Asia　(-4.0;　95%　UI:-5.7,-2.2),　despite　substantial　improvements　in　high-income　countries　(6.5;　95%　UI:　4.0,　8.5).　The　slope　index　of　inequality　decreased　from-15.48　(95%　confidence　interval　[CI]:-19.2,-11.76)　in　1990　to-8.49　(95%　CI:-12.26,-4.72)　in　2018.　Conclusions:　Our　findings　reveal　substantial　global　variations　in　mPHD　adherence　among　WAP,　with　concerning　trends　in　certain　regions.　These　results　provide　crucial　insights　for　developing　targeted　interventions　that　consider　regional　contexts　while　pursuing　the　dual　objectives　of　promoting　healthier　diets　and　ensuring　environmental　sustainability.