may be somewhat more protective in women than men.14
Although optimum body weight for older adults is higher than that for young adults, they tend to weigh less. The decline in body weight with age, as measured by BMI, has been well documented in population‐based, cross‐sectional, and longitudinal studies. For example, in the 1997–1998 US National Health Interview Survey of 68,556 adults, more people 75 and older than those 45–64 were ‘underweight’ (BMI <18.5; 5 vs. 1.2%) and substantially fewer were ‘overweight’ (BMI >25; 47.2 vs. 63.5%).15,16
Weight loss in older people
The lower average body weight of older than younger adults is not a function of survival from obesity‐related diseases. On average, people over 75 years of age are more likely to lose than gain weight. For example, in a study that followed 247 community‐dwelling American men age over 65 for two years, men lost on average 0.5% of their body weight per year, and 13.1% of the group had involuntary weight loss of 4% per annum or more. Numerous studies have shown that weight loss in the elderly is associated with poor outcomes, certainly if involuntary, but possibly even when deliberate. The prospective Cardiovascular Health Study, for example, studied 4714 home‐dwelling subjects over 65 without known cancer. In the three years after study entry, 17% of the subjects lost 5% or more of their initial body weight, compared with 13% who gained 5% weight or more. The weight‐loss group had significant increases in total (2.09 × ↑ [95% CI 1.67–2.62]) and risk‐adjusted mortality (1.67 × ↑ [95% CI 1.29–2.15]) over the following four years compared with the stable weight group. The increased mortality occurred irrespective of starting weight and whether or not the weight loss was intentional. The weight gain group had no increase in mortality. In the SHEP study mentioned above, subjects who had a weight loss of 1.6 kg per year or more experienced a 4.9 times greater death rate (95% CI 3.5–6.8) than those without significant weight change. Although mortality was also increased if weight increased more than 0.5 kg per year, the increase was less than that with weight loss (2.4‐ fold vs. 4.9‐fold increase). Of particular note, the adverse effects on mortality of weight loss were present even in the subjects who were heaviest at baseline (BMI ≥31) and were independent of baseline weight. The combination of initially low body weight and weight loss carries a particularly poor prognosis. In the SHEP study, subjects with a low baseline weight (BMI<23.6 kg−2 who lost more than 1.6 kg per year had a mortality rate of 22.6%, almost 20 times greater than the mortality rate of those with a baseline BMI of 23.6–28 kg−2 whose weight remained stable. This interaction is concerning since the tendency for older people to lose weight is variable, with lean individuals probably most at risk. In an older person, unintentional weight loss of 5% or more over 6–12 months is associated with an increased risk of adverse effects, and a loss of 10% or more very likely means protein‐energy malnutrition.12, 17–19
There are many reasons why weight loss in older people has adverse effects. In some cases, weight loss is due to an illness, such as a malignancy. Nevertheless, weight loss and associated undernutrition are significant problems because loss of body weight after age 60 is disproportionately of lean body tissue – that is, sarcopenia – and individuals lose up to 3 kg of lean body mass per decade after age 50. Unlike loss of fat tissue, such a loss of lean tissue has adverse effects. Sarcopenia is associated with metabolic, physiological, and functional impairments and disability, including increased falls and increased risk of protein‐energy malnutrition.20
Cachexia in older people
Weight loss and resulting adverse outcomes in older adults may be due to cachexia, malnutrition, the physiological anorexia of ageing, or some combination of these factors. Although there is often considerable overlap between them, cachexia and malnutrition are not the same. Whereas all cachectic patients are malnourished, not all malnourished patients are cachectic. Cachexia is a complex metabolic syndrome associated with underlying illness and characterized by loss of muscle with or without loss of fat mass. The prominent clinical feature of cachexia in adults is weight loss, but inflammation is a key component. Anorexia, insulin resistance, and increased muscle protein breakdown are also frequently associated with cachexia. Cachexia is distinct from starvation, age‐related loss of muscle mass, primary depression, malabsorption, and hyperthyroidism. Inflammation plays a major role in the pathogenesis of cachexia, with an absolute or relative increase in levels of inflammatory cytokines such as tumour necrosis factor alpha (TNF‐α), interleukin‐1, and interleukin‐6. Conditions that often afflict older people and that are frequently associated with cachexia include cancer, cardiac failure, chronic obstructive pulmonary disease and chronic renal failure. The European Society for Clinical Nutrition and Metabolism sub‐classified cachexia based on severity into cachexia and pre‐cachexia, the latter being present when there is (i) an underlying chronic disease, (ii) a systemic inflammatory response, (iii) anorexia, and (iv) unintentional weight loss over the previous six months of less than 5% of usual body weight.21,22
Causes of undernutrition in older people
Undernutrition in older adults is multifactorial, often mediated by reduced food intake, changes in physical and physiological status, changes due to chronic disease, the environment and related social determinants of health, and finally, iatrogenic causes.
Reduced food intake
Ageing is associated with a decline in energy (food) intake. Energy intake decreases by ~30% between ages 20 and 80.23 Elderly people on average consume smaller meals more slowly and fewer snacks between meals,1 and consistently report that they are less hungry than young adults.24 For example, the 1989 cross‐sectional American National Health and Nutrition Examination Survey (NHANES III) study reported a decline in energy intake between the ages of 20 and 80 of 1321 cal per day in men and 629 cal per day in women.25 A seven‐year New Mexico longitudinal study of 156 people age 64–91 reported a decrease of 19.3 kcal per day per year in women and 25.1 kcal per day per year in men,26 and a Swedish six‐year longitudinal study of 98 people found that between the ages of 70 and 76 there was a decrease in energy intake of 610 cal per day in men and 440 cal per day in women.27
Physical factors
Functional impairments that limit the completion of activities of daily living are also related to undernutrition. For example, immobility (e.g. stroke), tremor (e.g. Parkinson’s disease), and impaired vision may affect an older person's capacity to shop for, prepare, and consume food. Additionally, many older adults no longer have their own teeth. Poor dentition and ill‐fitting dentures may limit food type and quantity. For example, in one study, half of 260 nursing home patients, age 60–101, in Boston complained of problems with chewing, biting, and swallowing. The patients with dentures were more likely to have poor protein intake than those with their own teeth.28
Physiological changes
The older adult experiences several physiological changes that lend to anorexia: (i) loss of homeostasis, (ii) the ageing gut, (iii) declining senses, and (iv) hormonal andneurotransmitter changes. Numerous studies have documented an age‐related decline in appetite and energy intake in healthy, ambulant, non‐institutionalized people.23 Healthy older adults are less hungry and are more rapidly satiated after eating a standard meal than younger people. Much of this decrease in energy is likely a response to the decline in energy expenditure that also occurs during normal ageing.
Loss of homeostasis
Advanced age is associated with diminished homeostatic regulation of many physiological functions, including
