Obesity is defined as an excessive accumulation of fat, which may impair health and increase mortality. This disease is a serious nutritional problem, since it increases the risk and morbidity of various diseases, including hypertension, type 2 diabetes, coronary heart disease, stroke and certain types of cancer. Studies on the involvement of various minerals, such as magnesium, in the mechanisms underlying the pathogenesis of obesity, have been aimed at elucidating their contribution to comorbidities associated with obesity and oxidative stress in particular.  Oxidative stress is defined as an imbalance between the production of reactive oxygen species and antioxidant defences and has been implicated in potentially damaging effects, such as lipid peroxidation, DNA damage and intracellular signal transduction regulation. In this setting, it is the role of the antioxidant defence system to protect against oxidative stress present in obese individuals. It is emphasized that magnesium plays a role as an antioxidant, participating as a cofactor of several enzymes in cell membrane stabilization and mitigating the effects of oxidative stress. Magnesium is also involved in the metabolism of glucose in insulin homeostasis, and in adenosine triphosphate (ATP), protein and nucleic acid synthesis, and as a physiological regulator of hormone and immune function. Alterations in the homeostasis of this mineral can affect these functions, promoting the pathogenesis of obesity.  Several mechanisms are associated with oxidative stress in the presence of hypomagnesaemia in obesity. These include reduction in the activity of antioxidant enzymes, activation of inflammatory pathways, increased intracellular calcium concentration, lipid peroxidation induced by iron, insulin resistance and endothelial dysfunction. Studies have found that reduced intake of magnesium and low serum concentrations are strongly related to oxidative stress markers. The literature has shown that deficiency of this mineral contributes to susceptibility of cells to attack by reactive oxygen species.  In conclusion, studies on Mg help in clarifying its role in protection against oxidative stress, as well as identifying a possible need for its supple-mentation for the control of metabolic disorders associated with obesity.