It is possible to identify risks or protective factors against dementia. Increased levels of homocysteine (HCY) and vitamin B deficiency, obesity and central adiposity in midlife are independent risk factors for the development of dementia. High dietary intake of antioxidants and omega-3 fatty acids lower the risk of Alzheimer disease (AD). The supplementation with single nutrients, like vitamin B, omega-3-polyunsaturated fatty acids (PUFA) or antioxidants is generally not effective in lowering the risk of dementia or in slowing the progression of the disease. It is probably necessary that these nutrients are part of a healthy diet (with at least five portions of fruit and vegetables per day and one portion of fish per week) during the lite where other factors interact with them as it happens in the Mediterranean diet. Nutritional strategies for modifying the clinical course of cognitive failure should consider the use of nutritional screening tools in the multidimensional geriatric evaluation. Moreover, the diet, oral supplementation, caregiver education could be important factors to prevent or treat weight loss and its consequences in AD while the use of artificial nutrition in demented patients may have questionable benefits.