Detecting the existence of weight loss in the elderly is unlike many other diagnostic challenges because it requires the ability to see what is no longer there. It is like looking at two photos that at first glance appear similar until it becomes apparent that select and often obscure items in one are absent from the other. The failure to make this clinically essential assessment has profound implications. This is because weight loss is a common problem in older adults and has been associated with adverse outcomes, such as decreased functional status, institutionalization, and increased mortality.¹ Clinicians must understand that weight loss is not a normal part of aging and usually represents some underlying disease process, especially when it is an unexplained clinical finding in apparently healthy individuals.²,³ That weight loss may be one of the first clinical markers of Alzheimer disease underscores the importance of paying attention to what may be an easily overlooked data point.⁴ Weight loss remains independently associated with mortality even after adjustment for baseline health status.⁵

One study found that individuals who lost >10% of their body weight between the age of 70 and 75 had a significantly higher mortality risk during the following 5 years compared to those who lost <5%.⁶ Low body weight and weight loss are powerful predictors of morbidity including higher rates of infection, increased risk of decubitus ulcers, and poor response to medical therapy.⁷,⁸ This involutional process leads to and is a consequence of energy dysregulation, results in the atrophy of muscle, and accelerates the loss of independence.³

The fact that the average 75-year-old person has three chronic medical conditions and is on five prescription medications poses real challenges to the clinician caring for the aged. The sometimes evocative and occasionally urgent medical needs of the elderly have the potential to obscure what may be subtle changes that should trigger aggressive weight management.¹,⁹

Body weight is determined by a complex interaction of calorie intake, absorption, and utilization.⁷ The challenge of weight loss is multifaceted, with different clinical and metabolic effects depending on specific underlying triggers.

Low body weight in elders may reflect either their usual weight or a weight loss. Therefore, the most precise nutritional marker is measured weight loss over time because optimal weight in old age is a matter of considerable debate.¹⁰ A number of population studies have shown a U-shaped relationship of body mass index (BMI) with mortality and have indicated some surprisingly high body weights associated with the lowest mortality.¹⁰

Among healthy people, total body weight tends to peak in the sixth decade of life. Once weight has peaked, there is relative stability, with longitudinal studies demonstrating a weight loss of 1 to 2 kg per decade thereafter.⁷ In healthy elderly, there is an increase in fat tissue that balances a loss in skeletal muscle until very old age, when loss of both fat and skeletal muscle occurs.¹¹

Clinically important weight loss can be defined as the loss of 10 pounds (4.5 kg) or >5% of the body weight over a period of 6 to 12 months. This amount of weight loss is associated with a doubling of mortality over 4 to 5 years.¹² Weight loss of >10% represents protein-energy malnutrition and impaired physiologic function including impaired cell-mediated and humoral immunity.⁷ The challenge for physicians is that some patients may be undisturbed by their weight loss, or may even welcome it, and may mistakenly attribute the loss to their attempts to lose weight.⁷

There are a few key terms that have distinct definitions in weight management.

Cachexia: Weight loss may be a key feature, but cachexia more accurately represents the clinical consequences of chronic inflammation from a variety of causes. When weight loss due to cachexia occurs, it stems from the loss of fat-free mass, with muscle wasting as a key element. Cachexia is a kind of metabolic meltdown that often results in accelerated weight loss, loss of function, and a resistance to remediation. Cachexia may be associated with little or no weight loss in its early stages.

Sarcopenia: Sarcopenia specifically refers to decreased or diminished reserves of muscle and lean body mass.

Wasting: Wasting is the gradual loss of strength or substance. It is an unintentional loss of body weight (5% to 10%; BMI <28) coupled with a functional impairment in apparently healthy individuals, with loss in both the fat and fat-free compartments.

Failure to Thrive: Failure to thrive is weight loss, decreased appetite, poor nutrition, and inactivity, often accompanied by dehydration, depressive symptoms, and impaired immune function.

BMI: BMI is the ratio of weight in kg to the square of height in meters. Normal BMI for the elderly is 20 to 30.

Body Cell Mass: Body cell mass is the fat-free portion of cells within muscle, viscera, and the immune system.

The process of normal aging has inherent mechanisms that result in; changes in fat and muscle distribution, changes in taste and smell, and alterations in gastric and intestinal motility, all of which can affect appetite. These processes in combination with age-related changes in activity will ultimately result in incremental weight loss independent of any disease state. Among aging healthy people, total body weight peaks in the sixth decade of life.⁷ This is the norm in developed nations where adult weight, which increases during middle age, generally remains stable in the healthy elderly until the ninth decade and then gradually falls.¹¹ Once an individual’s weight has peaked, there is relative stability in total weight in the healthy elderly.⁷

However, lean body mass (fat-free mass) begins to decline at a rate of 0.3 kg per year in the third decade, and at age 60 in men and 65 in women the rate increases to a 0.5% annual decline in lean body mass.¹³,¹⁴ These weight changes are largely attributed to a decline in physical activity. In the healthy elderly, an increase in fat tissue balances a loss in skeletal muscle mass until very old age, when the loss of both fat and skeletal muscle loss occurs.¹¹ Because fat-free mass declines as much as 40% between the age of 30 and 70, at any given body weight or BMI, older persons will be considerably fatter than their younger counterparts.¹

There are also changes occurring at a cellular level, which reflect changes in cellular composition and associated intrinsic physiologic processes. Body cell mass is the fat-free portion of cells within the muscle, viscera, and immune system. Body cell mass declines steadily with age in healthy, successfully aging people. This mass is important because it directly predicts strength, and therefore functional status, and is the major determinant of energy needs.¹⁵

There are physiologic mediators of weight loss in healthy individuals that may also be mediators in the presence of disease and debilitation. Some loss of lean body mass is due to age-related declines in anabolic hormones (e.g., growth hormone, dehydro-3-epiandrosterone, and sex hormones), the adverse effects of accumulated free radicals, increased cytokines (interleukin-6 [IL-6] and tumor necrosis factor-α [TNF-α]), and the effects of intermittent acute illness and reduced activity levels.¹ These changes are interrelated with age-related loss of smell and taste and intestinal motility disorders such as constipation, gastroparesis, and dyspepsia.¹⁶ Collectively, there seems to be a steady transformative process that leads to some degree of sarcopenia, even in successfully aging adults, and is universal. It is difficult to know whether the sarcopenia seen in the elderly is due to decreased physical activity or whether it leads to decreased physical activity.¹⁵

Therefore, it becomes apparent that normal weight changes in the elderly are the result of interrelated mechanisms that may originate at the level of intracellular processes reflected in cell composition and that may then impact digestive physiology, which leads to changes in compartmentalization of fat and muscle mass. These phenomena contribute to a decline in appetite, leading to a decline in the ingestion of nutrients needed to sustain physical activity that is required to delay or forestall loss of muscle mass, weakness, and sarcopenia—apoptosis at work.

The previous section details weight changes that are incremental and are consistent with the process of healthy aging. There is also a physiologic weight loss that is due to a gradually decreased intake of food throughout life. Between the age of 20 and 80, the mean energy intake is reduced by up to 1,200 kcal per day in men and 800 kcal in women. This is believed to be the result of decreased hunger, reflecting reduced physical activity, decreased REE, and loss of lean body mass, all producing lower demand in calories and food intake.² This is the physiologic weight loss (below the threshold of 5% annual weight loss) seen as a consequence of aging.

We will now examine the causes of weight loss that are nonphysiologic and exceed the 5% threshold. This is what may be considered protein-energy malnutrition, which is highly prevalent among the elderly and which, in addition to leading to an underweight condition, is an important cause of age-related declines in muscle mass.¹⁷ Proteinenergy malnutrition is often due to multiple factors. A circuitous relationship often exists among the causes that makes the isolation of a pivotal event or process and the subsequent development of a clinical approach to treatment challenging and, to a degree, frustrating. This unintentional or involuntary weight loss is associated with self-rated poor health, chronic disability, cancer, respiratory diseases, diabetes, and cardiovascular events such as heart attack and stroke.¹⁸

The term nutritional frailty is used to describe a dramatic decline in appetite and drastic decline in food intake. There can be a precipitous drop in body weight over a period of weeks and months that is recognized as a hallmark of terminal and unremediable decline.² When it is due to an illness, the prognosis is grave. However, when no definitive cause can be identified, patients may be amenable to treatment and have a better prognosis.⁷

Weight is mediated primarily by one’s appetite. So long as an individual has adequate access to sources of food
with sufficient caloric content and has the ability to eat independently or with assistance, intake and consequently one’s weight is directly related to appetite. The mechanisms that maintain a healthy appetite are not completely understood.¹⁹ Seemingly simple disruptions in physiologic processes that physicians may deem of little consequence in younger populations can have profound effects in the elderly. Peptic ulcer disease or gastroesophageal reflux disease may lead to loss of appetite.¹⁹ A decrease in relaxation of the fundus of the stomach can result in early antral filling, causing early satiation.¹³ Low-fat and sodium-restricted diets do not taste as good and are associated with weight loss, low albumin level, and orthostasis in nursing home patients.¹⁴ Some patients with a history of anorexia nervosa relapse later in life and develop what is called anorexia tardive.¹⁴ Causes of involuntary weight loss are listed in Table 10.1.

One of the most ominous causes of unintentional weight loss is cancer. In one series of patients, malignancies were the cause of weight loss in one third of all patients. The most common cancers were gastrointestinal, hepatobiliary, hematologic, lung, breast, genitourinary, ovarian, and prostate.⁷