The effects of exercise training status on appetitive, metabolic, and endocrine responses in older adults

John William Apolzan, Purdue University

Abstract

Aging is associated with a loss of skeletal muscle mass resulting in reduced physical function. The loss of muscle mass leads to increased body fat, decreased metabolic rate, reduced strength, and reduced functional status. A possible reason for the loss of muscle mass and strength is physical inactivity. Physical activity attenuates muscle loss and may decrease impairment of energy regulation. Aging is also associated with a dysregulation of appetite and energy intake. In the extremes, dysregulation can lead to anorexia or obesity. Weight loss may contribute to malnutrition, falls, and increased mortality. Weight gain increases risk for metabolic risk factors contributing to increased mortality. The purpose of these studies is to gain a better understanding of appetite and energy regulation in exercising, older adults. In the first study, to assess the effects of physical activity status and age on appetite sensations, older men and women were recruited into 4 groups: younger inactive (n=13, 25±6y), younger active (n=11, 25±5y), older inactive (n=16, 69±4y), older active (n=16, 72±5y). Each subject rated waking hour feelings of hunger, fullness, and desire to eat hourly for 1 non-exercising day. Physical activity status did not affect appetite sensations. Mean hunger (<0.05) and desire to eat (p<0.01) were lower in the older vs. younger adults, but no differences were shown with feelings of fullness. Thus physical activity status does not influence appetite or the age-associated changes in hunger and fullness on a non-exercising day. In the second study, the effects of chronic resistance training on fasting appetite-related hormones (CCK, GLP-1, ghrelin, glucose, and insulin), 3-day free-living appetitive sensations (hunger, desire to eat, and fullness), and food intake were assessed in 16 (7M, 9F) resistance trained and 35 (15M, 20F) untrained older adults aged 62-84y. In resistance trained vs. untrained individuals, fasting CCK concentration was higher (p<0.05) and fasting GLP-1 concentration was lower (p<0.05), but fasting glucose and ghrelin were not different. Resistance trained males insulin concentration was not different than untrained males, untrained females, or resistance trained females, but untrained females had higher fasting insulin concentration than untrained males and untrained females (p<0.05). In resistance trained vs. untrained adults, hunger and desire to eat were not different. Fullness was lower in the resistance trained vs. sedentary groups (p=0.05). Total energy intake, protein, carbohydrate, and fat intake were not affected by resistance training. Daily area under the curve (AUC) appetite sensation values were not correlated with any appetite-related hormone. Daily appetite sensations did not influence energy intake suggesting fasting appetite-related hormones do not affect appetite sensations. With resistance trained vs. untrained older adults, differences in appetite regulation were observed, but no differences in energy intake were seen. In the third study, the effects of food form and chronic resistance training were assessed in 16 resistance trained and 18 sedentary older male and female adults 62-84y. On two separate days, subjects consumed an isoenergetic, macronutrient matched beverage and solid. Appetite sensations (fullness, hunger and desire to eat), energy expenditure and appetite-related hormones (glucose, insulin, CCK, GLP-1, and ghrelin) were evaluated over 4 h using hourly trapezoidal area under the curve. Fullness was lower after solid vs. beverage and in resistance trained men vs. sedentary males and resistance trained females but not the sedentary females. Hunger and desire to eat were not different with food form, and hunger was not affected by resistance training status but desire to eat was lower in resistance trained men. Postprandial energy expenditure was not different regarding food form or training status. Independent of training status, glucose, and insulin were higher in solid vs. beverage form. CCK was higher following ingestion of the solid vs. beverage and in resistance trained vs. sedentary older adults. GLP-1 was not affected by food form but was higher in the resistance trained vs. sedentary group (p<0.01). Males had higher postprandial ghrelin concentrations after solid vs. beverage ingestion (p<0.05), but females did not respond differently to the test meals. Meal replacement products consumed in solid and beverage forms should not be considered as appetitive or endocrine equivalents in older people who are sedentary or more physically active and use resistance training to achieve higher strength. Older adults, especially men, may benefit from incorporating resistance training and beverage meals to potentially reduce the anorexia of aging. Collectively, these results suggest that alterations in appetite sensations and appetite-related hormones occur with food form and resistance training. Older persons who are prone to anorexia of aging should consider consuming additional energy from beverages, while persons prone to obesity should consume foods in solid form while maintaining or initiating a resistance training program to attenuate muscle loss and decrease the effects of energy dysregulation accompanied with aging.

Degree

Ph.D.

Advisors

Campbell, Purdue University.

Subject Area

Gerontology|Endocrinology|Nutrition|Kinesiology

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