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Exposure to low levels of environmental challenges, known as hormetic stress, fosters subsequent stress resistance and promotes healthy aging in later life. However, specific mechanisms governing transcriptional reprogramming upon hormetic nutrient stress remain elusive. Here, we identify histone H3 lysine 27 acetylation (H3K27ac) as a crucial driver of transcriptomic adaptation to hormetic fasting. Beyond its immediate function of enhancing lipid catabolism for alternative energy sources, stress-induced H3K27ac activates lifelong antioxidant defenses, thereby reducing reactive oxygen species (ROS) produced by stress-induced fatty acid oxidation and their accumulation during aging. Induced H3K27ac at metabolic genes, mediated by the pioneer factor PHA-4/FOXA, the cooperating transcription factor NHR-49/HNF4, and the nucleoporin 50 (NPP-16/NUP50), is crucial for lifespan extension under hormetic nutrient stress in Caenorhabditis elegans. Our findings establish H3K27ac as a key transcriptional switch bridging nutrient status with transcriptomic reprogramming, underpinning the longevity of hormetic fasting through orchestrating lipid catabolism and antioxidant defenses.