Weight loss is frequent in Alzheimer's disease. Its severity increases with the progression of the disease and may be a predictor of patients' mortality. Weight loss often precedes the diagnosis and may be considered as a feature of the disease itself. With the progression of the disease, disorders of eating behavior occur and result in weight loss and decreasing energy intake. Descriptive tools such as the Blandford Scale are helpful to assess eating disorders. Some hypotheses exist to explain the weight loss associated with Alzheimer's disease: atrophy of internal temporal cortex, increase of energy expenditure, biologic factors or modifications of body composition. Tools such as the Mini Nutritional Assessment allow assessment of nutritional status, diagnosis of malnutrition, cause identification and proposals for its correction. Patients' caregivers play a central role in prevention and management of nutritional disorders. Information programs for caregivers may reduce caregiver burden and improve patients' health status.