Abstract Background: Mounting evidence implicates diets high in fats and processed sugars with increased generation of free radicals in animals. It is still not clearly established whether such a diet alters antioxidant balance in dementia patients, where an oxidative stress status may already exist. The disruption to lipid metabolism by oxidative stress has been recently linked to neurodegeneration and clinical disease. The aim of this study is to assess the relationship between fat, sugar, carbohydrate and caloric intake levels, and antioxidant status in patients with mild to moderate dementia. Methods: The levels of 3 essential endogenous antioxidants (superoxide dismutase, catalase, glutathione peroxidase) were measured in the blood of 26 dementia subjects and 26 cognitively unimpaired controls. Concurrently, the intake levels of relevant nutrients and dietary antioxidants were assessed in all subjects. Results: A statistically significant positive association was observed in the dementia group between glutathione peroxidase activity and the intake of fats (r=0.44; p=0.023), carbohydrates (r=0.46; p=0.018), total sugars (r=0.51; p=0.007) and calories (r=0.47; p=0.14). The only significant association in the control group was observed between glutathione peroxidase and fat (r=0.47; p=0.015). Conclusion: The higher glutathione peroxidase activity among subjects with greater intake of fats, carbohydrates and sugars may represent a compensatory response to the additional increase in oxidative stress in dementia. Our data shed light on the influence of dietary intake on the oxidant-antioxidant system in mild to moderate dementia patients.