Understanding the economic costs attributable to unhealthy diets is essential for advocating health and agrifood investments in low- and middle-income countries (LMICs) experiencing nutrition transitions. These costs encompass direct and hidden expenses, including absenteeism, presenteeism, and premature mortality. Recent estimates highlight that overweight and obesity contribute 2.2% of global GDP, with significant human costs reflected in millions of deaths associated with noncommunicable diseases (NCDs), predominantly in LMICs. The World Bank projects that by 2035, obesity's hidden costs in LMICs will reach US$7 trillion. The State of Food and Agriculture (SOFA) 2024 report estimates global agrifood systems' hidden costs at over US$10 trillion at 2020 purchasing power parity, with 70% linked to unhealthy diets. These findings underscore the need for reformulating agrifood fiscal policies to promote healthy diets and reduce economic losses. This report employs a novel methodology to assess the economic costs of child stunting and adult diet-related NCDs attributable to unhealthy diets. Using the Lives Saved Tool (LiST), the study estimates that significant portions of child stunting costs in Ethiopia and the Philippines are due to suboptimal diets. For adult populations, the Global Diet Quality Score (GDQS) was utilized to analyze diet quality and its association with NCD risk factors such as high body mass index (BMI), systolic blood pressure (SBP), and fasting blood glucose (FBG). Results indicate widespread unhealthy diets across all BMI categories, suggesting that estimates based solely on overweight and obesity may underestimate actual costs. The report concludes that while the methodology provides valuable insights into the economic impacts of unhealthy diets, limitations such as outdated data and the need for robust dietary intake measures in LMICs must be addressed. Further research is necessary to refine these estimates and support policy development aimed at reducing diet-related economic burdens.