Muscle mass, BMR and energy intake tend to decline with age   This is mainly due to declining activity levels rather than to the ageing process. A lower BMR means one needs to eat less in order to maintain the same body weight, thus making a nutritionally adequate diet difficult to achieve. Careful food selection is required if one is not physically active   This is especially true in later years; great care is needed with food selection to ensure that all essential nutrients are obtained without becoming over-fat. Higher energy and nutrient intakes accompany increased physical activity   This has been shown to prolong life, prevent muscle loss, and prevent frailty and falls in the aged.

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Some of the most dramatic changes that we see with age are changes in body composition. A decline in muscle mass and increases in body fat tend to occur, as people grow older. However, what is often not appreciated is that these too cannot be blamed on the aging process per se. A major contributor to these changes is the increasingly sedentary nature of people's lifestyles as they grow older. Reduced physical activity leads to loss of muscle, and as a direct consequence basal metabolic rate falls. Several studies have shown that energy and total food intakes decline with age making a nutritionally adequate diet more difficult to achieve. Older men consume about 800 kcal less than younger men and older women about 400kcal less than younger women. A reduction in basal metabolic rate is partly responsible for this decline, but physical inactivity appears to be the major cause for reduced food intake. A lower metabolic rate means that we need to eat less in order to maintain the same body weight. If one does indeed eat less in order to avoid weight gain, rather than remaining (or becoming) active, it becomes increasingly difficult to meet the needs for essential nutrients.

Compared with younger adults, older adults need to reach at least the same levels of intake (and in some cases, higher levels) of most vitamins, minerals and protein. However, since this usually needs to be obtained in a substantially lower overall food intake, a nutrient/ phytochemically dense diet becomes a high priority in later life. In other words, given the tendency for activity levels to decline and total food intakes to fall with advancing years, there is less room for energy dense foods (e.g indulgences, treats) which supply few of the essential nutrients which our bodies continue to need. Therefore, older adults need be selective about what they eat to avoid excessive fat gain and prefer foods that are nutrient dense and high in protein e.g nuts, lean red meat, low fat dairy products, legumes, seeds. This principal also applies to younger adults who are sedentary. Without doubt, it is preferable to keep physically active to enable a higher energy intake through the maintenance of muscle mass, and continue to enjoy eating.

Physical activity has been associated with greater energy intakes and subsequently nutrient intakes and quality of life in the aged. It prolongs life and in the aged compresses morbidity towards the end of life. Prospective studies show that increased energy intakes of the order of 300-500 kcal per day, which is balanced with increased physical activity to avoid fat gain, confer either decreased cardiovascular or total mortality, and improve life expectancy. This results in a higher plane of energy nutrition. This runs counter to the disturbing advocacy, that energy restriction prolongs life. These studies were conducted on rats and have no direct application to humans. To suggest that elderly people restrict their food intake to prolong life is absurd when this may contribute to 'frailty' and loss of lean mass. The evidence is, however, that any extra energy intake must be from nutrient (and phytochemical) dense foods, without excessive abdominal fatness.

James WPT. Energy. In: Nutrition in the elderly. Horwitz A, Macfdyen DM, Munro H, Scrimshaw NS, Steen B, Williams TF (eds). The World Health Organization. New York: Oxford University Press 1989:49-64; Kushi et al. Diet and 20 year mortality from cornonary heart disease. The Ireland-Boston Diet Heart Study. NEJM 1985; 312: 811-8.; Kromhout D. The protective effect of a small amount of fish on coronary heart disease mortality in an elderly population. Int J Epidemiol 1995; 24:340-345. Paffenbarger RS The association of changes in physical-activity level and other lifestyle characteristics with mortality among men. N Engl J Med 1993; 328: 538-45.

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