Taste and Smell
Diet And Nutrition
There is no dramatic decline in taste or smell function in healthy aging. Rather, a subtle and gradual decline in sensitivity begins around middle age and continues in later life. Smell losses hinder the ability to identify familiar odors and reduce the perceived intensity of flavors in food. Taste losses, if present, are often localized and whole mouth taste sensation is often not affected.
The impact of such losses on diet, nutrition, and health has not always been clear. Some researchers have argued that irreversible changes in taste and smell lead directly to altered food preferences, reduced food consumption, and poor nutrition. However, very few studies have controlled for the subjects’ health status. As noted above, sensory deficits may result not from advanced age but from ill health. Moreover, very few studies have examined taste or smell function, dietary intakes, and nutritional status in the same persons.
For example, it is unclear whether reduced perception of saltiness leads to increased salt intakes among older adults. One study found that older subjects needed twice as much salt to detect its presence in tomato juice as did young subjects. More than half of middle-aged subjects and older subjects (age sixty-seven to eighty-nine) failed to detect the presence of salt in soup. However, there is no clear relationship between the detection of saltiness and preference for salt. Some studies on salt taste preferences reported that older subjects preferred saltier mashed potatoes and chicken broth than did young people, while others found no age-related increase in preference for salt in soup or in tomato juice. These studies did not speak to the key question of whether changes in salt taste perception affect intake of saltier foods on a regular basis.
Findings that older subjects sometimes prefer higher concentrations of sugar and salt in both water and other beverages were interpreted to mean that they would select sweeter and saltier foods. However, food consumption was not actually measured. Very few studies measured salt taste perception, salt taste preference and actual salt consumption among the same respondents. In one such study, young and older adults did not differ in their saltiness intensity ratings for chicken broth. Moreover, older adults generally preferred lower salt concentrations in chicken broth. The hedonic response to salt in soup was not related to daily sodium intakes as assessed by fifteen days of diet records. Sodium intakes (expressed as mg per 1,000 kcal) did not increase with age.
The ability to perceive bitter taste also declines with age. Age was also the strongest predictor of food preferences. Older women expressed increased liking (or reduced dislike) for cruciferous vegetables and bitter salad greens. The reduced response to bitter may increase the acceptance of some bitter foods by women.
The age-associated decline in the sense of smell is also thought to have nutritional consequences. Some scientists believe that olfactory deficits reduce the pleasantness of foods and are the direct cause of reduced food intake and malnutrition in the elderly. A study of smell in eighty older women (sixty-five to ninety-three years of age) showed that half had severe olfactory dysfunction. The dysfunction did not affect appetite, and was unrelated to total energy intake, body weight, or the body mass index (BMI). Body mass index, weight divided by the square of height (1kg/m2), is a measure of body mass. However, women with smell losses reported a lower interest in food-related activities (e.g., enjoying cooking, eating a wide variety of foods); lower preference for foods with sour/bitter taste, such as citrus fruits; higher intake of sweets; and higher intake of fats. Smell losses may lead people to select foods that are sweet or rich in fat, such that the taste and texture will contribute to sensory appeal.
Amplifying foods with noncaloric flavors is thought to be a promising approach in promoting energy intake by older persons and reversing age-related anorexia. In one such study, 75 percent of elderly subjects preferred foods that had been amplified or enhanced with added flavor. In some cases, carrots were amplified with carrot flavor; in other cases, peas were enhanced with bacon flavor or cauliflower with a cheese flavor. The results showed that flavor enhancement, as opposed to a simple flavor amplification, was the more effective method. The most effective enhancers of food intake among older persons were synthetic meat flavors: bacon, roast beef, and ham.
Data from nutritional surveys suggest that dietary variety, defined as the number of different foods consumed each day, often declines with age. This effect was not observed among healthy older people of means, but is reported to be common among institutionalized persons. Researchers believe that the mechanism of sensory-specific satiety encourages the consumption of a varied diet. Sensory specific satiety reduces preference for the just-consumed foods and foods much like them. In contrast, preferences for new foods are maintained at higher levels. In laboratory studies, sensory-specific satiety diminished with age and was lowest in persons over sixty-five. Though the reason for this reduction was unclear, it was unlikely to be caused by any deficits in sensory function.
Consumer studies show that food choices are very largely determined by how foods taste. However, economic factors and health concerns also play a role. Demographic and psychosocial factors have a major impact on the quality of the diet of older adults. When it comes to food choices, deficits in taste and smell, if present, can be compensated for by prior learning and experience.
ADAM DREWNOWSKI SUSAN E. COLDWELL BARBARA J. ROLLS
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