In western societies, overeating and obesity is a major health problem. This does include older people as well, with more than fifty percent of Americans over the age of 65 having a Body Mass Index (BMI) of 25 kg/m2 or over, a value considered a cutoff for being characterized as overweight by the World Health Organisation. Although weight loss seems beneficial for young adults, this is not necessarily the case for the elderly. Numerous studies have shown that weight loss in the elderly is associated with poor outcomes, certainly if weight loss is involuntary, but possibly even when it is deliberate.
Energy restriction in the elderly is likely to result in loss of lean body mass, nutritional deficiencies, reduced function, and adverse effects. For these reasons, caution should be exercised in recommending significant calorie restriction to people over the age of seventy. There is evidence that the adverse effects of being overweight are not as great in the elderly as in younger adults. The ideal weight seems to be higher in the elderly and there is evidence that a body mass index above normal seems to have a more protective impact especially in women as compared to men.
Elderly people, however, demonstrate in general gradual weight loss, as documented in epidemiological studies. Studies have shown that there is an involuntary weight loss of 0.5-5% of body weight per year. At the same time, numerous studies have shown that involuntary weight loss in the elderly is associated with poor outcomes. There are many reasons why weight loss in older people has adverse effects. It some cases, weight loss is due to an illness, such as an underlying malignancy. In these cases, it is the malignancy which is mainly responsible for the poor outcome and the weight loss is partly an ‘innocent bystander’. Nevertheless, the weight loss and associated undernutrition are themselves often a significant problem. This is because a loss of body weight after the age of 60 years represents disproportionately loss of lean body tissue, what is known as sarcopenia. On average individuals lose up to 3 kg of lean body mass per decade after the age of 50 years. Unlike the 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, diminished strength and increased risk of protein-energy malnutrition. What is important to understand is that an elderly person may be sarcopenic, without demonstrating significant weight loss. So individuals with a high body mass index may demonstrate what is known as sarcopenic obesity.
Older persons tend to eat fewer calories than younger adults due to several reasons that are related to physiological changes (reduced appetite, reduced resting energy expenditure), socioeconomic and psychological reasons (depression, isolation, loneliness) or pathologic causes such as difficulty in chewing (e.g. problems with their teeth or dentures), problems with swallowing (neurodegenerative diseases) or anorexia due to serious underlying conditions (cancer, heart or kidney failure etc).
Another mechanism for weight loss in the elderly is cachexia, a combined protein and energy store loss due to the effects of disease. Cachexia is an inflammatory response mediated by molecules called cytokines. Patients with cachexia lose roughly equal amounts of fat and fat-free mass. Common conditions associated this cachexia are amongst others, infections like AIDS or tuberculosis, cancer, end-stage kidney disease, rheumatoid arthritis, chronic obstructive pulmonary disease and congestive heart failure.
Weight loss can also occur due to anorexia, the lack of appetite. This can be a result of underlying acute illness or occasionally may also result from changes in the physiological regulation of appetite and satiety, as a physiological response to aging. A lot of interest and discussion focuses on the effects of dementia in the nutritional status of the elderly. As the disease progresses, malnutrition may manifest itself as a result of many factors. In advanced stages of dementia, there is a reduced capacity for communication, loss of pleasure in eating, changes in mastication leading to difficulty in swallowing certain consistencies of food, and culminating in dysphagia. Also, advanced dementia may be related to the presence of higher rates of infection, the burning of energy due to repetitive movements and cognitive deficit that compromises the patient’ s independence.