INTRODUCTION:
Obesity and unsustainable food systems represent interconnected global issues that exacerbate health inequities, environmental degradation, and social exclusion. With over 1 billion people affected by obesity worldwide, as reported by The Lancet (Phelps et al., 2024), unsustainable dietary patterns—dominated by processed foods and animal products—drive non-communicable diseases while contributing to one-third of greenhouse gas emissions and resource depletion. This perspective study examines their bidirectional nexus through a Health in All Policies (HiAP) framework, emphasizing equity, inclusion, and sustainability to achieve health without borders.

METHODS:
Employing a systems lens, we synthesize evidence from global studies on dietary impacts, metabolic food waste, and policy inertia. A conceptual HiAP framework is developed to integrate cross-sectoral actions in agriculture, urban planning, education, and trade, with a focus on health impact assessments and multi-stakeholder collaboration to promote inclusive, equitable interventions.

RESULTS:
Unsustainable diets heighten obesity risks through inflammation, oxidative stress, and nutrient deficiencies, while obesity amplifies environmental burdens via increased food demand and waste. HiAP enables double-duty policies, such as taxing unhealthy foods, subsidizing plant-based options, and regulating marketing, to reduce disparities and foster sustainable, inclusive food environments. Case studies, like Seinäjoki's multi-sectoral approach, demonstrate reductions in childhood obesity through equitable access to healthy, sustainable resources (Koivusilta et al., 2022).

CONCLUSIONS:
HiAP offers a transformative pathway to disrupt the obesity-sustainability syndemic, ensuring equity and inclusion in global health strategies. By prioritizing cross-border collaboration and systemic reforms, we can advance sustainable diets, mitigate health inequities, and build resilient, inclusive societies for planetary and human well-being.