<p>How do expert committees sustain credibility while radically expanding their institutional scope? This question animates contemporary food governance, as dietary guidelines, historically focused on nutritional adequacy, increasingly incorporate environmental sustainability and demands for democratic participation. Yet scholarship has largely neglected the ongoing legitimacy work, the strategic framing, methodological commitments, and communication practices through which expert bodies navigate such frame expansion. This study takes the Nordic Nutrition Recommendations 2023 (NNR2023) as a critical case, analysing how experts reconciled scientific authority with environmental values and public participation. Drawing on in-depth expert interviews and an extensive documentary corpus, and bringing framing theory into conversation with a further developed, three-dimensional account of legitimacy, we distinguish epistemic, procedural, and cultural registers, the last of which we elaborate beyond its conventional treatment to foreground civic epistemologies and Nordic food cultures. Our findings show that these dimensions constantly pull against one another: methodological hardening strengthened epistemic authority yet narrowed participation; radical transparency enhanced fairness yet exposed disagreements; cultural accommodation honoured national foodways yet strained universalist claims. Rather than resolving these tensions, experts managed them through what we term “performed legitimacy,” an ongoing, audience-relational accomplishment that may suggest the contours of a more reflexive expert governance for an era of integrative food policy.</p>