Nutrient excess is known to lead to mitochondrial dysfunction with consequential effects on lipid and glucose metabolism. Mitochondrial dysfunction in adipose tissue has been reported in patientswith obesity or type 2 diabetes. Mitochondrial DNA copy number, and mitochondrial mass and activity are decreased in the white adipose tissue of mouse
models of obesity. In humans, there is a correlation between downregulation of the expression and activity of the components of oxidative phosphorylation in white adipose tissue and obesity. Dysfunctional mitochondriamay lead to oxidative stress through excessive production of reactive oxygen species (reactive oxygen species). Indeed, oxidative stress is associated with adiposity and lipid peroxide levels, and hydrogen peroxide generation is elevated in adipose tissue, but not in skeletalmuscle or the aorta. Considering that mitochondria are the most important source of intracellular reactive oxygen species, it is possible that the adipose tissue in obese individuals represents a major source of reactive oxygen species. In human studies, the extent of fat accumulation has been correlated with various markers of systemic oxidative stress.