AMPK regulates energy expenditure by modulating NAD+ metabolism and SIRT1 activity. This study shows that AMPK activates SIRT1 by increasing NAD+ levels, leading to the deacetylation and modulation of SIRT1 targets, including PGC-1α and FOXO1/3a. This process enhances energy metabolism by promoting mitochondrial biogenesis, oxidative metabolism, and fatty acid oxidation. AMPK-induced SIRT1-mediated deacetylation of PGC-1α is crucial for its transcriptional activity, which in turn regulates mitochondrial and lipid metabolism genes. The study also demonstrates that AMPK activates PGC-1α through both direct phosphorylation and indirect deacetylation by SIRT1. The NAD+/NADH ratio is increased by AMPK activation, which activates SIRT1. This study highlights the interplay between AMPK and SIRT1 in regulating energy homeostasis and metabolic functions. The findings suggest that AMPK and SIRT1 work together to modulate energy expenditure and metabolic health.AMPK regulates energy expenditure by modulating NAD+ metabolism and SIRT1 activity. This study shows that AMPK activates SIRT1 by increasing NAD+ levels, leading to the deacetylation and modulation of SIRT1 targets, including PGC-1α and FOXO1/3a. This process enhances energy metabolism by promoting mitochondrial biogenesis, oxidative metabolism, and fatty acid oxidation. AMPK-induced SIRT1-mediated deacetylation of PGC-1α is crucial for its transcriptional activity, which in turn regulates mitochondrial and lipid metabolism genes. The study also demonstrates that AMPK activates PGC-1α through both direct phosphorylation and indirect deacetylation by SIRT1. The NAD+/NADH ratio is increased by AMPK activation, which activates SIRT1. This study highlights the interplay between AMPK and SIRT1 in regulating energy homeostasis and metabolic functions. The findings suggest that AMPK and SIRT1 work together to modulate energy expenditure and metabolic health.