5.5 Older adults and the elderly

Many age-related changes that influence energy requirements occur continually throughout the adult life cycle. A decline in BMR with age has been recognized since the studies of Keys, Taylor and Grande (1973), who estimated it at a rate of 1 to 2 percent per decade. Average decreases of 2.9 and 2.0 percent per decade, respectively, for men and women of normal weight (BMI of 18.5 to 25.0 kg/m²) were calculated more recently (Roberts and Dalall, 2001; Food and Nutrition Board/Institute of Medicine, 2002). The decreases were 3.1 and 1.9 percent per decade among overweight men and women, respectively (Roberts and Dalall, 2001). The decline is not linear, and has a suggested breakpoint at about 40 years of age in men and 50 years in women (Poehlman, 1992; Poehlman et al., 1993). The organization of the data in Table 5.10 by decades points to a breakpoint at about 50 years of age for both genders. This decrease in BMR has been explained partly by the reduction in fat-free mass that occurs with ageing, and by changes in the composition of that fat-free mass (Piers et al., 1998). Several studies, however, suggest that even after adjusting for changes in fat-free mass, BMR is 5 percent lower in older persons compared with young adults (Roberts and Dalall, 2001).

On the other hand, body weight tends to increase with age in many societies. For example, there are more overweight men and women (defined as BMI > 25) than people with BMI £ 25 in the database of the United States Academy of Sciences (Table 5.10) (Food and Nutrition Board/Institute of Medicine, 2002). The largest series currently available of TEE and BMR measurements in people 70 to 79 years old involved 150 men and 150 women randomly recruited in two large cities of the United States. Average weight and BMI were 82.4 kg and 27.4 among men, and 70.6 kg and 27.3 among women (Blanc et al., 2001). Overweight and obesity increase BMR and TEE owing to the increase in the fat-free mass needed to carry the extra weight and to the increased energy cost of activities. However, BMR per unit of body weight is reduced in overweight and obese subjects owing to the larger gain in fat mass relative to metabolically active fat-free mass.

Habitual physical activity, and hence TEE, decrease after a given age (Black et al., 1996; Roberts, 1996). However, studies with standardized activity protocols in a whole body calorimeter did not show differences in TEE between young and old adults (Vaughan, Zurlo and Ravussin, 1991; Pannemans and Westerterp, 1995). Furthermore, although maximal oxygen consumption decreases progressively with age (Suominen et al., 1980), some elderly individuals who have remained physically active are able to maintain high levels of energy expenditure, with PAL values as high as 2.48 (Reilly et al., 1993; Withers et al., 1998). This indicates that the age at which TEE and energy requirements start decreasing depends on individual, social and cultural features that promote or limit habitual physical activity among older adults.

Calculation of energy requirements for the elderly based on PAL is highly dependent on the accuracy with which BMR is measured or estimated. For example, the preliminary TEE results - and therefore energy requirements - of 70 to 79 year-old people in a United States study on health, ageing and body composition (Blanc et al., 2001) were 10.1 ± 1.8 MJ/day for men, and 8.0 ± 1.5 MJ/day for women. Based on actual measurements of BMR (men: 5.9 ± 0.1 MJ/day BMR; women: 4.8 ± 0.1 MJ/day BMR), mean PAL was 1.72 among men and 1.68 among women, but using the predictive equations in Table 5.2, PAL would be 1.55 for men and 1.47 for women. The error in prediction may have been associated with the excessive weight of this population group.

In conclusion, energy requirements for older adults and the elderly should be calculated on the basis of PALs, just as they are calculated for younger adults. Therefore, the accuracy with which BMR of older adults can be estimated becomes of primary importance. As more reliable information on BMR of older adults with differing lifestyles, body composition and physical activity becomes available, it may be necessary to revise the predictive equations for this age group in order to make better estimations of their energy requirements. Allowances must be made for population groups who are more or less active at an advanced age, rather than using age as the single cut-off point to define energy requirements for the elderly.

TABLE 5.10
Daily energy expenditure, basal metabolic rate and physical activity level measured in United States adults

Sources: Roberts and Dallal, 2001; Food and Nutrition Board/Institute of Medicine, 2002.

5.6 Recommendations for regular physical activity

The practice of regular physical activity is associated with the maintenance of adequate body weight, cardiovascular and respiratory health, and fitness,^[5] and a lower risk of developing chronic non-communicable diseases associated with diet and lifestyle (Erlichman, Kerbey and James, 2001; WHO, 2000; WHO/FAO, 2002; Pollock et al., 1998; Ferro-Luzzi and Martino, 1996; Schoeller, 1998; WHO, 2002; Erlichman, Kerbey and James, no date; American Heart Association, 2002; IARC, 2002; CDC, 1996; World Cancer Research Fund/American Institute for Cancer Research, 1997; Saris et al., 2003). Consequently, dietary energy recommendations to satisfy requirements should be accompanied by recommendations to perform adequate amounts of physical activity regularly.

There is consensus among experts that a habitual PAL of 1.70 or higher is associated with a lower risk of overweight and obesity, cardiovascular disease, diabetes and several types of cancer (Black et al., 1996; Erlichman, Kerbey and James, 2001; Pollock et al., 1998; Ferro-Luzzi and Martino, 1996; Schoeller, 1998; Erlichman, Kerbey and James, no date; World Cancer Research Fund/American Institute for Cancer Research, 1997; Saris et al., 2003). Therefore, it is particularly important to recommend regular physical activity to populations and individuals with a sedentary lifestyle or one of light activity. Those with moderately or vigorously physically active lifestyles already have a habitual physical activity close to, or higher than, the health-associated PAL threshold of 1.70 times BMR. Recommendations for these individuals should be aimed at the maintenance of that activity level.

5.6.1 Frequency, duration and intensity of physical activity

Table 5.11 summarizes the minimum amounts of exercise, expressed in terms of frequency, duration and intensity, advocated by several organizations to maintain and promote health among adults (WHO/FAO, 2002; Pollock et al., 1998; WHO, 2002; American Heart Association, 2002; IARC, 2002; CDC, 1996; World Cancer Research Fund/American Institute for Cancer Research, 1997; Saris et al., 2003). The conclusions reached in the cited publications can be summarized as follows:

• There is consensus that, in order to promote general health, at least 30 minutes of moderate to vigorous activity should be performed, three or more days per week.

• Sedentary people and those with low physical fitness levels will benefit from the lower amounts of exercise prescribed in Table 5.11 (i.e. 30 minutes of moderate activity, three days per week). To obtain increased benefits, those with better conditions should exercise longer and/or at a higher intensity (e.g. 60 minutes of moderate or vigorous activity, five or more days per week).

• Longer periods of exercise are required to maintain a healthy body weight and to reduce the risk of obesity than are needed to help reduce the risk of chronic diseases such as coronary heart disease and diabetes mellitus.

• Sixty minutes of daily exercise have been advocated to increase the PAL of sedentary people to a value of 1.75 or greater, assist in weight maintenance and play a part in the prevention of some types of cancer, especially colorectal and breast cancer.

• Any activity that is rhythmic and aerobic in nature, uses large muscle groups and can be maintained continuously is recommended for general health and fitness. Activities that can be practised as part of everyday life are particularly useful. Examples include brisk walking, climbing stairs, cycling, dancing, jogging/running, hiking, low-impact aerobic exercises, swimming, skipping rope, ice/roller skating and various endurance games and sport activities.

• Duration is related to intensity. Thus, when ranges are given in Table 5.11 (e.g. 30 to 60 minutes at 50 to 80 percent capacity), lower-intensity activity should be conducted over a longer period of time (i.e. 60 minutes at 50 percent capacity [moderate activity], or 30 minutes at 80 percent aerobic capacity [vigorous activity]).

• An activity regimen of moderate- rather than high-intensity exercise is recommended, and total fitness is more readily attained with longer sessions. Consequently, it may be better to suggest activity of moderate intensity for 60 minutes than of high intensity for 30 minutes.

• Although longer sessions are generally preferable, their duration may hinder compliance among some people. In these cases it may be appropriate to recommend accumulated bouts of activity for shorter durations throughout the day (e.g. 15 minutes two or four times daily, instead of 30 or 60 minutes once daily).

TABLE 5.11
Minimum frequency, duration and intensity of physical activity advocated by selected organizations

^a Endorsed by the joint WHO/FAO Expert Consultation on Diet, Nutrition and the Prevention of Chronic Diseases (FAO/WHO, 2002).

For general populations, particularly those with sedentary occupations, a joint WHO/FAO Expert Consultation on Diet, Nutrition and the Prevention of Chronic Diseases (WHO/FAO, 2002) recently advocated the performance of moderate-intensity activity, such as brisk walking, for a total of one hour per day on most days of the week to help maintain a healthy body weight and reduce the risk of co-morbid diseases associated with overweight. This level of exercise may be considered part of the daily routine of people with occupations entailing moderate or vigorous, energy-demanding physical activity for one or more hours, five or more days per week.

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