Some older people may overly restrict foods important to good health because of chewing difficulties and gastrointestinal disturbances, such as constipation, diarrhea and heartburn. Because missing teeth and poorly fitting dentures make it hard to chew, older people may forego fresh fruits and vegetables, which are important sources of vitamins, minerals and fiber. Or they may avoid dairy products, believing they cause gas or constipation. By doing so, they miss out on important sources of calcium, protein and some vitamins.
Adverse reactions from medications can cause older people to avoid certain foods. Some medications alter the sense of taste, which can adversely affect appetite. This adds to the problem of naturally diminishing senses of taste and smell, common as people age.
Other medical problems, such as arthritis, stroke or Alzheimer's disease, can interfere with good nutrition. It may be difficult, if not impossible, for example, for people with arthritis or who have had a stroke to cook, shop, or even lift a fork to eat. Dementia associated with Alzheimer's and other diseases may cause them to eat poorly or forget to eat altogether.
From the FDA