Quantifying metabolic food waste and associated global warming potential attributable to overweight and obese adults in a temperate high-income region

Traditional discussions on food waste often excludes metabolic food waste (MFW), which occurs when individuals consume food beyond their caloric needs. This study is the first to quantify MFW among adults with excess body weight (overweight and obese) in the Republic of Ireland (ROI) and globally the first to explore its socioeconomic and health-related predictors. Using an online food frequency questionnaire, MFW was estimated via the excess energy intake method, and Generalized Linear Model (GLM) was applied to identify significant predictors of MFW volumes. Median per capita MFW was 121.84 kg/year, with potatoes being the most wasted food item (23.4 kg/year). Significant predictors of higher MFW included higher body weight (B = 0.024, p < 0.001), male gender (B = −0.812, p < 0.001), younger age (25–34 years) (B = 0.151, p = 0.035), omnivorous diets (B = 0.277, p < 0.001), and higher grocery shopping frequency (B = 0.032, p < 0.001). Conversely, individuals who prioritized price over taste in food purchases exhibited significantly lower MFW volumes (B = −0.137, p = 0.025). The annual total volumes of MFW (0.3 Mt./yr) generated by excess body weight adults in ROI is also responsible for 1.5 Mt. CO₂e/yr emissions nationally. These findings position MFW as a critical yet underexplored dimension of food waste with profound implications for public health and environmental policies, aligning with SDGs 2 (Zero Hunger), 3 (Good Health and Well-being), and 12 (Responsible Consumption and Production).