What's Happening in the Brain
Control of appetite is complex, and not well understood. A lot of brain chemicals are involved, and while classically appetite is disrupted later in Alzheimer's disease , it can also be seen even in mild Alzheimer's disease, or before a diagnosis is made. Of course, sometimes, a decreased appetite reflects in decreased sense of smell and taste, which is seen in some people a few years before Alzheimer's disease starts.
There are several theories about why weight loss occurs in Alzheimer's disease. Many people believe that it reflects a 'more active metabolism', but there is little evidence to suggest that this is the case. What seems more likely is that certain aspects of the inflammatory response that occurs in Alzheimer's disease release chemicals that break down muscle , as well as having some effect on fat stores. This might be one reason that tube feeding is often ineffective in Alzheimer's disease. In addition, the part of the brain known as the hypothalamus is important in appetite control, especially the brain chemical called leptin. Studies about leptin and associated chemicals that control the sense of having eaten enough are an active area of inquiry by scientists interested in Alzheimer's disease.
People who are depressed often have a disrupted appetite. It is therefore worth having the person you care for evaluated for depression .