In the United States we are currently experiencing the phenomenon of the “graying of America,” whereby the population is growing older and the proportion of those 65 years and older is rapidly increasing. Data from the U.S. Census Bureau predict that the number of individuals 65 years and older will double in the next 20 years. Most of this growth is happening in the “oldest old”—that is, 85 years and older. Among other challenges, the aging of the population brings the increasing burden of chronic disease conditions such as diabetes, hypertension, and heart disease (1), all of which are known risk factors for chronic kidney disease (CKD) (2). In addition, aging is associated with many changes, including those that have an adverse impact on physiologic, metabolic, and functional status. Specific changes in body composition and the function of organ systems alter the requirements for energy, fat, protein, micronutrients, and fluids.
It has been shown that markers of malnutrition—including hypoalbuminemia, hypocholesterolemia, and low body mass index—are associated with poor outcomes such as increased hospital length of stay, complications, readmissions, functional impairment, and mortality (3–5). This leads to higher use of health care resources by the elderly population. Hence, it is extremely important that malnutrition in elderly persons is recognized early and treated appropriately.
Advancing age is characterized by a progressive loss of lean body mass and a relative increase in fat mass (6). There is also redistribution of fat from peripheral to central locations within the body. Most of the loss in lean body mass is due to reduction in muscle mass, a condition called sarcopenia. The muscle content of the body is important because of the central role of muscle mass in physical function and strength, and because of the association of sarcopenia with increased morbidity and mortality (7, 8). A lack of physical activity is crucial to the development of sarcopenia but is not the sole cause of it. Various hormonal, neural, and proinflammatory cytokines seem to play a role as well (9).
Malnutrition is an important problem that is seen in elderly community-dwelling individuals (10) and in those who are institutionalized (11). Many changes associated with aging can promote malnutrition. Poor appetite is a major cause. Energy and protein intake decrease with age (12), and this decrease can lead to nutritional deficiencies. Various hormones and cytokines (13) are thought to be involved in the regulation of appetite, and age-related changes in these can lead to decreased appetite and early satiety. Changes in taste and smell sensations can lead to loss of appetite through a perceived decline in the pleasantness of food (14). Deteriorating oral health and dentition have been shown to significantly affect food intake. The UK National Diet and Nutrition Survey showed that energy and protein intake is lower in edentate individuals.
Many disease states are associated with higher rates of malnutrition in the older populations. Declining cognitive state, depression, and other psychological factors have been associated with weight loss and malnutrition in the elderly. In addition, many medications have adverse effects that can alter the taste sensation and the appetite, thus further exacerbating nutritional deficiencies.
The dietary protein requirements of the elderly are believed to be higher, and for many reasons. The phenomenon of anabolic resistance leads to resistance to the positive effects of dietary protein on the synthesis of protein (15). Conditions associated with chronic inflammation, such as heart failure, CKD, and chronic obstructive pulmonary disease, add to protein needs. Hence, the imbalance due to increased protein needs and decreased protein intake leads to negative nitrogen balance, which in turn is responsible for frailty and sarcopenia in the elderly. These conditions can lead to functional dependence, falls, fractures, and even death.
Frailty and sarcopenia can be prevented to an extent by increasing protein energy intake and by regular exercise (16, 17). Studies have shown that aging muscle does respond to exercise. Progressive resistance training in older adults can lead to improved physical function (18).
The protein needs of older people may be somewhat higher than was originally thought. The recommended dietary allowance (RDA) for protein in healthy adults of all ages has been set at 0.8 g/kg body weight/day. However, there is evidence to support an increase in the RDA for protein to 1.0 to 1.2 g/kg body weight/day for adults older than 65 years (19, 20). Under conditions of stress or injury, protein requirements are even higher and are estimated at 1.5 g/kg body weight/day. These needs have to be balanced with requirements in certain disease states such as renal or hepatic insufficiency, which may require protein restriction to prevent worsening of these conditions and the development of further complications. This is particularly important in patients with CKD, in whom an uncontrolled high-protein diet may have harmful effects on the progression of kidney disease and on various other metabolic abnormalities. Before a high-protein diet is recommended to an elderly person with CKD, it is thus important to assess the risk of progression of kidney disease versus the risk for development of malnutrition. Mild kidney disease in an elderly person is unlikely to progress to ESRD; hence, a normal-protein or high-protein diet is recommended. In elderly patients with moderate CKD (i.e., estimated GFR of 30–60 mL/min/1.73 m2) the risk versus benefit needs to be assessed before any dietary protein recommendations can be made. On the other hand, in elderly patients with severe CKD (estimated GFR <30 mL/min/1.73 m2) protein intake of 0.6 to 0.8 g/kg body weight/day is recommended unless there is a clear indication of a need for higher intake (21).
In summary, elderly individuals experience changes in body composition and therefore protein and energy demands change, making malnutrition a greater risk. Although adequate protein intake is important, the presence of liver and kidney disease needs to be carefully considered before any dietary protein recommendations are made.
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