Understanding anorexia in the elderly: formulating biopsychological research strategies

Chromatographic analysis of age-related changes in mucosal serotonin transmission in the murine distal ileum

BACKGROUND

In the upper bowel, alterations in motility and absorption of key nutrients have been observed as part of the normal ageing process. Serotonin (5-HT) is a key signalling molecule in the gastrointestinal tract and is known to influence motility, however little is known of how the ageing process alters 5-HT signalling processes in the bowel.

RESULTS

An isocratic chromatographic method was able to detect all 5-HT precursors and metabolites. Using extracellular and intracellular sampling approaches, we were able to monitor all key parameters associated with the transmission process. There was no alteration in the levels of tryptophan and 5-HTP between 3 and 18 month old animals. There was a significant increase in the ratio of 5-HT:5-HTP and an increase in intracellular 5-HT between 3 and 18 month old animals suggesting an increase in 5-HT synthesis. There was also a significant increase in extracellular 5-HT with age, suggesting increased 5-HT release. There was an age-related decrease in the ratio of intracellular 5-HIAA:extracellular 5-HT, whilst the amount of 5-HIAA did not change with age. In the presence of an increase in extracellular 5-HT, the lack of an age-related change in 5-HIAA is suggestive of a decrease in re-uptake via the serotonin transporter (SERT).

CONCLUSIONS

We have used intracellular and extracellular sampling to provide more insight into alterations in the neurotransmission process of 5-HT during normal ageing. We observed elevated 5-HT synthesis and release and a possible decrease in the activity of SERT. Taken together these changes lead to increased 5-HT availability and may alter motility function and could lead to the changes in adsorption observed in the elderly.

Nutrition and Aging: Changes in the Regulation of Energy Metabolism With Aging

Changes in energy regulation occur during normal aging and contribute to the common phenomenon of weight and fat losses late in life. This review synthesizes data on aging-related changes in energy intake and energy expenditure and on the regulation of energy intake and expenditure. The ability of older adults to accurately regulate energy intake is impaired, with a number of possible explanations including delayed rate of absorption of macronutrients secondary to reductions in taste and smell acuity and numerous hormonal and metabolic mediators of energy regulation that change with aging. There are also changes in patterns of dietary intake and a reduction in the variety of foods consumed in old age that are thought to further reduce energy intake. Additionally, all components of energy expenditure decrease with aging, in particular energy expenditure for physical activity and basal metabolic rate, and the ability of energy expenditure to increase or decrease to attenuate energy imbalance during overeating or undereating also decreases. Combined, these changes result in an increased susceptibility to energy imbalance (both positive and negative) in old age that is associated with deteriorations in health. Practical interventions for prevention of weight and fat fluctuations in old age are anticipated here based on emerging knowledge of the role of such factors as dietary variety, taste, and palatability in late-life energy regulation.

A general model of intake regulation

Previously proposed models of intake regulation focus on specific variables thought to influence overall intake, and include factors involved in negative feedback loops with intake as well as genetic influences on intake. Recent evidence, however, suggests that these models although informative, are incomplete. They cannot account for the observations of prolonged and increasing deviations from defended levels, weakness and transitoriness of compensatory responses, the presence of powerful factors that are not compensated, and behavioral genetic data suggesting that there are a wide variety of independent genetic influences on numerous factors that influence intake. As a result we propose a new general model of intake regulation in which intake is influenced by both a set of uncompensated factors that are not influenced by intake and by a set of compensated factors that are. The preferred levels of intake and both sets of factors are specified as influenced by heredity. Further, the model includes impact factors, weights, which specify the magnitude of the effect each factor has on intake. The weights are assumed to be different for different individuals and their values are determined by heredity. A computer simulation of the new model demonstrated that it maintains different levels depending upon the external and internal environments, that changes in these environments result in new levels, and that inherited individual differences in responsiveness to these factors can markedly influence the levels obtained. The proposed general model appears to fit existing knowledge and is parsimonious and widely applicable. Future work should be directed to testing the general model and further developing specific models within the conceptual framework employing known physiological systems and uncompensated stimuli.

Flavor enhancement of food improves dietary intake and nutritional status of elderly nursing home residents

BACKGROUND

Taste and smell losses occur with aging. These changes may decrease the enjoyment of food and may subsequently reduce food consumption and negatively influence the nutritional status of elderly persons, especially those who are frail. The objective of this study was to determine if the addition of flavor enhancers to the cooked meals for elderly residents of a nursing home promotes food consumption and provides nutritional benefits.

METHODS

We performed a 16-week parallel group intervention consisting of sprinkling flavor enhancers over the cooked meals of the "flavor" group (n = 36) and not over the meals of the control group (n = 31). Measurements of intake of the cooked meals were taken before and after 8 and 16 weeks of intervention. Appetite, daily dietary intake, and anthropometry were assessed before and after the intervention.

RESULTS

On average, the body weight of the flavor group increased (+1.1 +/- 1.3 kg; p <.05) compared with that of the control group (-0.3 +/- 1.6 kg; p <.05). Daily dietary intake decreased in the control group (-485 +/- 1245 kJ; p <.05) but not in the flavor group (-208 +/- 1115 kJ; p =.28). Intake of the cooked meal increased in the flavor group (133 +/- 367 kJ; p <.05) but not in the control group (85 +/- 392 kJ). A similar trend was observed for hunger feelings, which increased only in the flavor group.

CONCLUSION

Adding flavor enhancers to the cooked meals was an effective way to improve dietary intake and body weight in elderly nursing home residents.

Glutamate and the UMAMI taste: sensory, metabolic, nutritional and behavioural considerations. A review of the literature published in the last 10 years

Monosodium glutamate (MSG) is used increasingly often in processed foods and in home cooking in the Western world. This substance is responsible for a pleasurable taste sensation, the Umami taste. This review covers recent developments in sensory studies of glutamate effects, and traces the Umami taste from sensory receptors on the tongue to the brain. The metabolism of glutamic acid, as revealed from recent literature, is described. A specific section is devoted to safety issues. In addition, effects of glutamic salts on nutrition and ingestive behaviours are shown to be potent. Animal and human works are treated separately, with special attention to the specific methods used in both cases. Future areas of research include further investigation of sensory physiology, role of glutamate as an excitatory substance in the brain, acquisition of food likes and impact on long-term food selection, food intake, and body weight control.

Effects of monosodium glutamate on human food palatability

Monosodium glutamate (MSG) is a well-known flavor enhancer used in both Western and Eastern cuisines. Responsible for the 'umami' (delicious) taste, it is incorporated into a large number of solid and liquid savory foods. Experimental studies have established that the presence of added MSG in foods influences palatability, preference and selection. Sensory evaluation tests have shown that both traditional and novel foods get higher palatability ratings if MSG is added at an appropriate dose. In young adults, behavioral tests have shown that the acquisition of a liking for novel foods is facilitated by the addition of MSG to the recipe. In institutionalized elderly persons as well as hospitalized diabetic patients, the addition of MSG to target foods in a lunch meal induced an increased intake for those specific foods, with a subsequent decreased intake of foods presented later in the meal. In both populations, only prandial food selection was affected by MSG, but meal size (kJoules) remained the same. Experiencing the positive effects of MSG is thus possible without inducing hyperphagia. In conclusion, MSG can be used casually by the consumer in order to increase palatability, and it can also be used selectively by nutrition experts in order to orient food selection toward a healthy diet composition.

Monosodium glutamate as a palatability enhancer in the European diet

Can monosodium glutamate (MSG) augment palatability in foods of the occidental diet? Its effects on the palatability of two experimental foods were investigated in 36 healthy young men and women. MSG improved palatability ratings, with an optimum at 0.6%. Weekly tests of free intake showed that subjects fed the experimental foods with 0.6% MSG added ate progressively more and faster, indicating increasing palatability with repeated exposure. The effects of MSG on familiar foods were investigated in a group of 65 institutionalized elderly persons. Spontaneous intake was measured at lunch time on 12 test days. Target foods (soup and vegetable) were served either without or with 0.6% MSG added. MSG facilitated intake of some but not all target foods, and was associated with positive (increased calcium and magnesium intake) or adverse (increased fat intake) nutritional effects. It is concluded that MSG can act as a palatability enhancer in the context of the French diet. It can facilitate long-term intake in both young and elderly persons but it should be utilized cautiously so as to improve nutrition.