Many animal studies have shown that life expectancy can be extended by restricting food intake. It is, however, not known whether the ageing process in humans can be altered by nutrition.
The ageing process
The process of ageing is not well understood. While wear and tear may play a role, it is an insufficient explanation for the causation of ageing. A number of theories have been postulated.
Programmed ageing theory suggests a predetermined, presumably genetic, age-related alteration in cellular function that leads to susceptibility to disease and death.
Genomic instability theory suggests errors in genetic transcription and translation, resulting in impaired protein synthesis and deterioration in cell function as age increases.
Free radical theory suggests that these highly reactive molecules are no longer metabolized rapidly; accumulation occurs, leading to irreversible cell damage.
Random genetic errors have also been implicated; an accumulation of errors over time is said to result in impaired protein synthesis and a decrease in cellular function.
Several other mechanisms have been suggested, but it is still unclear whether one universal or several independent mechanisms are involved.
Nutritional requirements in the elderly
These are qualitatively similar to the requirements of 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 requirement of 'elderly people' (aged 60 and above, irrespective of age) has been set to be approximately 1.5 × BMR. The BMR is reduced, owing to a fall in the fat-free mass, from an average of 60 kg to 50 kg in men and from 40 kg to 35 kg in women. The diet should contain the same proportions of nutrients, and essential nutrients are still required.
Nutritional deficits in the elderly may be due to many factors, such as dental problems, lack of cooking skills (particularly in widowers), depression and 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 because often these people do not go into the sunlight.
Owing to the high prevalence of osteoporosis in elderly people, daily calcium intake of 1-1.5 g/day is often recommended.