Many animal studies have shown that life expectancy can be extended by restricting food intake. It is, however, not known in humans whether the ageing process can be alteredby nutrition.
THE AGEING PROCESS
While wear and tear may playa role in ageing, it does not appear to be a sufficient explanation for the occurrence of ageing. A number of theories have been postulated.
PROGRAMMED AGEING. This theory suggests a predetermined, presumably genetic, age-related alteration in cellular function that leads to susceptibility to disease and death.
THE GENOMIC INSTABILITY THEORY suggests errors in genetic transcription and translation resulting in impaired protein synthesis and deterioration in cell function as age increases.
THE FREE RADICAL THEORY OF AGEING suggests that these highly reactive molecules are no longer metabolized rapidly so that accumulation occurs leading to irreversible cell damage.
RANDOM GENETIC ERRORS have also been implicated and an accumulation of errors over time is said to result in impaired protein synthesis. Several other mechanisms have been suggested, but it is still unclear whether there is one universal or several independent mechanisms involved.
NUTRITIONAL REQUIREMENTS IN THE ELDERLY
These are qualitatively similar to younger adults, but as energy expenditure is less, there is a lower energy requirement. However, maintaining physical activity is required for the overall health of the elderly. The daily energy requirements of the elderly have recently been set to be approximately 1.5 x BMR (age 60 and above, irrespective of age). The BMR is reduced due to a fall in the fat-free mass from an average of 60 to 50 kg in men and from 40 to 35 kg in women. The diet should contain the same proportion of nutrients and essential nutrients are still required.
NUTRITIONAL PROBLEMS are due to many factors, such as dental problems, lack of cooking skills, particularly in elderly widowers, depression and sometimes lack of motivation. Significant malnourishment in developed countries is usually secondary to social problems or disease. In the elderly who are institutionalized, vitamin D supplements may be required as often patients do not go into the sunlight.
Due to the high prevalence of osteoporosis in elderly people, daily calcium intake should be between 1 and 1.5 g.