Final answer:
The primary reason for malnutrition, muscle and weight loss in the geriatric population is high levels of malnutrition resulting from a lack of access to a diverse diet with adequate sources of protein.
Step-by-step explanation:
The primary reason for malnutrition, muscle and weight loss in the geriatric population is high levels of malnutrition resulting from a lack of access to a diverse diet with adequate sources of protein. This is especially prevalent in developing countries where undernutrition is a major issue. Additionally, certain diseases and conditions can cause malnutrition, such as cancer, inflammatory bowel syndrome, AIDS, Alzheimer's disease, and psychiatric illnesses like anorexia. Furthermore, physical inactivity and atrophy, as well as protein-energy malnutrition, can contribute to muscle and weight loss in the geriatric population.