The pervasive use of polyethylene (PE) bags for cooking and storing staple Nigerian foods poses significant health risks due to heavy metal leaching. This study evaluates the migration of arsenic (As), cadmium (Cd), lead (Pb), and antimony (Sb) from transparent (TPB) and black (BPB) polyethylene bags into Garri, Semovita, Moi Moi, and Okpa under cooking conditions. Food samples, prepared using ingredients from Umuahia markets, were cooked in TPB and BPB, digested with nitric acid and aqua regia, and analysed via Atomic Absorption Spectrophotometry (AAS). Results revealed alarming contamination: BPB-cooked foods exhibited higher metal transfer, with Pb in Okpa (0.4801 mg/kg) and Cd in Moi Moi (0.3150 mg/kg) exceeding WHO/FAO limits (0.3 mg/kg Pb; 0.1 mg/kg Cd). Significant correlations emerged between As-Sb (r = 0.974, p = 0.0256) in uncooked samples and As-Cd (r = 0.9932, p = 0.000672) in cooked foods, highlighting synergistic leaching risks. Transparent bags also exhibited elevated levels of contamination, although these levels were 20–30% lower than those found in BPB-cooked foods. These findings underscore chronic exposure risks, including carcinogenicity and organ damage. Immediate actions are urged: enforcing bans on non-food-grade plastics, promoting biodegradable alternatives (e.g., plantain leaves), and launching public health campaigns to mitigate dietary heavy metal exposure. This study provides critical evidence for policymakers to prioritize food safety regulations in Nigeria and similar contexts by emphasizing feasible transitions to sustainable packaging.