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Weight loss, together with psychological and behavioural symptoms and problems of mobility, is one of the principal manifestations of Alzheimer's disease (AD). Weight loss may be associated with protein and energy malnutrition leading to severe complications (alteration of the immune system, muscular atrophy, loss of independence). Various explanations have been proposed such as atrophy of the mesial temporal cortex, biological disturbances, or feeding behaviours; however, none has been proven. Prevention of weight loss in AD is a major issue. It requires regular follow-up and must be an integral part of the care plan. The aim of this article is to review the present state of scientific knowledge on weight loss associated with AD. We will consider four points: the natural history of weight loss, its known etiological factors, its consequences and the various management options.

AGE-RELATED LOSS IN MUSCLE MASS: Aging is associated with a progressive decline in muscle mass (sarcopenia). Age-related sarcopenia results in a 50% decrease in muscle fiber area, especially type II fiber area. There are many consequences related to this reduction in muscle mass including decline in muscle strength and function and impaired functional capacity. PROTEIN INTAKE: Sarcopenia also results in a reduction in the body's major protein pool. Adequate dietary protein to replace obligatory nitrogen loss and to support protein turnover is essential for maintaining muscle mass. It is usually suggested that protein requirements in older subjects are above 1 g/kg/d. PHYSICAL EXERCISE: Sedentary lifestyle may contribute to loss of skeletal mass in elderly people. Exercise can help reverse this deficit and may improve the regeneration potential of muscle fibers.