Cachexia: Physical wasting with loss of weight and muscle mass caused by disease. Patients with advanced cancer, AIDS, and some other major chronic progressive diseases may appear cachectic. Cachexia is a wasting syndrome that causes weakness and a loss of weight, fat, and muscle. Anorexia (lack of apppetite) and cachexia often occur together. Cachexia can occur in people who are eating enough, but who cannot absorb the nutrients. Cachexia is not the same as starvation. A healthy person's body can adjust to starvation by slowing down its use of nutrients, but in cachectic patients, the body does not make this adjustment.