1.3.2. Malnutrition
Malnutrition is defined as a state in which a deficiency, excess, or imbalance of energy, protein, and other nutrients causes measurable adverse effects on tissue and body form (body shape, size, and composition), function, and clinical outcomes [48]. It is more prevalent as age increases [49,50,51]. The etiology of malnutrition is multifactorial; adverse physiological, psychological, and social causes of malnutrition in older adults are consistently reported in the literature [52]. Aging is accompanied by physiological changes that can negatively impact nutritional status, for example, sensory impairment may result in reduced appetite and poor oral health, and dental problems can lead to difficulty chewing, inflammation, and a monotonous, poor-quality diet. Progressive loss of vision and hearing may also limit mobility and affect the ability to shop for food and prepare meals [53,54].
In addition to loneliness and depression, other psychosocial and social changes characteristic of older adults, such as cognitive impairment, heavy use of medication, periods of lengthy hospitalization, retirement from paid work, bereavement, and increasing frailty can also contribute to poor nutritional status [54,55]. These factors affect the ability of older adults to meet dietary needs or to digest, absorb, utilize, or excrete nutrients that are ingested, leading to reduced energy intake and lean body mass. This, in turn, may result in a reduced metabolic rate, a corresponding decline in total energy expenditure, and potentially to malnutrition [56,57,58]. Thus, malnutrition, like other unhealthy outcomes of old age, may also be associated with subjective age [45].