Obesity

Excessive accumulation of body fat.

Total body fat (visceral and nonvisceral) increases until about age 40 in men and age 50 in women and then remains steady until age 70, after which it decreases. The decrease is due to loss of both lean and adipose tissue. Percentage of body fat peaks at middle age and may decline slightly in extreme old age. Intra-abdominal and intramuscular fat increases with age. Visceral body fat also tends to increase with age.

Fat acts as a storage organ for excess calories, providing protection during times of acute illness. Fat also protects vital organs from injury during falls and plays an important role in maintaining core body temperature. The excessive accumulation of body fat, however, may cause certain medical complications in the elderly (see Table 62-1). A low waist-to-hip ratio protects against some of these complications. An increased waist-to-hip ratio suggests an increase in visceral fat, which in turn is associated with increased risk of hypertension, diabetes mellitus, coronary artery disease, and premature death. Women have lower waist-to-hip ratios than men.

Persons who weigh 120 to 130% of their desirable weight are considered moderately obese; those who weigh more than 130% of their desirable weight are considered morbidly obese. In the USA, the prevalence of obesity in men is highest during middle age, declining to 26% by age 65 to 74. The prevalence in women is highest between ages 65 and 74 (36% for whites and 60% for blacks). In nursing homes, only morbid obesity has been associated with increased mortality.

Animal studies, particularly in rodents, have shown that dietary restriction may improve longevity. Primate studies are beginning to suggest that dietary restriction produces some biochemical improvements associated with longevity. However, the ideal body mass for an elderly person has not been established, although it is probably higher than that for a younger person.

Etiology

In elderly men, obesity appears to result from a decrease in physical activity; in elderly women, from the loss of estrogen; and in both sexes, from decreased levels of growth hormone. Genotype appears to account for 25% of a person's visceral body fat, ie, about 25% of the visceral fat pool is attributable to genes.

Overeating coupled with a decrease in physical activity and resting metabolic rate is the most common cause of obesity. Compared with younger men, elderly men experience a 20% decrease in total energy expenditure. Elderly women, however, experience only a minimal change in total energy expenditure. The explanation for this is that men tend to markedly reduce their physical activity with retirement, whereas women continue doing the bulk of the housework throughout their life. Resting metabolic rate decreases by 20% in men and 13% in women. These age-related reductions in resting metabolic rate result from a small decrease in triiodothyronine levels, reduced responsiveness to norepinephrine, reduced muscle tone and strength of muscle contraction, and reduced Na⁺,K⁺-ATPase activity. However, the major factor affecting resting metabolic rate is decreased food intake with age. Nonsmoking women aged 55 to 74 consume 300 kcal/day less than women aged 19 to 29; for men, the decrease is 950 kcal/day. Elderly persons also have a decreased thermic response to food.

Other causes of obesity include hypothyroidism, Cushing's syndrome, tumors of the ventromedial hypothalamus, and therapy with glucocorticoids, monoamine oxidase inhibitors, and moderate doses of phenothiazines.

Treatment

Obesity generally is a less important problem in elderly persons than in younger persons. The risk/benefit ratio of any therapeutic intervention should be evaluated. Some evidence suggests that excessive weight loss in elderly persons is associated with increased mortality.

Because the major identifiable cause of weight gain in elderly persons is lack of physical activity, an exercise program is the most reasonable approach to weight reduction. Walking 1 mile burns about 100 kcal. Thus, a mall-walking program in which a person walks 2 to 3 miles four times a week may induce gradual weight loss, as long as caloric intake is restricted. For persons with osteoarthritis, an upper body exercise program is recommended.

The diet of elderly persons trying to lose weight should provide at least 800 kcal/day and should always be supplemented with vitamins and trace minerals. Elderly persons on a weight-reduction diet should drink at least 1 L of fluid daily. Any dietary program should be supplemented with a behavior modification program, because a change in lifetime habits is often needed. Because of the risk of developing protein deficiency, an elderly patient on a weight-reduction diet should have his albumin level monitored monthly. If the level falls below 3.5 g/dL (35 g/L), a high-protein diet should be prescribed or the current diet discontinued. Rarely is a weight-reduction diet indicated for long-term nursing home residents.

Weight-loss drugs such as sibutramine or fluoxetine are not recommended for the elderly, because the possible benefits do not outweigh the adverse effects. Orlistat (an inhibitor of fat absorption) may be useful for obese elderly persons, particularly those with diabetes mellitus or hypertension.

Any operation that decreases stomach size is contraindicated in the elderly unless obesity is associated with sleep apnea.