As we age, our immune response capability becomes reduced, which in turn contributes to more infections and more cancer. As life expectancy in developed countries has increased, so too has the incidence of age-related conditions.
With age comes many physical changes. Once the body reaches physiologic maturity, the rate of degenerative change exceeds the rate of cell regeneration. However, people age at different rates, so the elderly population is not a homogeneous group; there is great variability among individuals.
The following are typical physiologic changes that can affect nutritional status:
Body composition changes as fat replace muscle, in a process called sarcopenia. Research shows that exercise, especially weight training, slows down this process. Because of the reduction in lean body mass, basal metabolic rate (BMR) declines about 5% per decade during adulthood. Total caloric needs drop and reduced protein help slow the body's ability to respond to injury or surgery. Body water reduces along with the reduction in lean body mass.
Gastrointestinal (GI) changes contain a decrease in digestion and absorption. Digestive hormones and enzymes decrease, the intestinal mucosa deteriorates, and the gastric emptying time increases. As a result, two conditions are more likely: pernicious anaemia and constipation. Pernicious anaemia may result because of hypochlorhydria, which reduces vitamin B absorption. Constipation, despite much laxative use among older people, may result from slower GI motility, insufficient fluid information, or physical inactivity.