The independent and combined effects of caffeine and exercise on eating behavior
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The purpose of this dissertation is to define and describe eating behavior, describe the known mechanisms and effects of caffeine on exercise and examine the independent and combined effects of caffeine and short-term exercise on eating behavior. Study 1,between subjects design, randomized inactive adults to different frequencies (0, 1, 3, 5 days/week) of short-term (2 weeks) aerobic exercise and measured the reinforcing value and consumption of healthy versus unhealthy foods baseline to post-treatment. Study 2, within subjects design, randomized adults to three relative caffeine doses (0, l, and 3 mg/kg body weight) and measured the effects of acute caffeine exposure on appetite and intake at breakfast and throughout the day. Study 3, between subjects two-by-two design, randomized inactive adults to different conditions (short-term no exercise/exercise) and treatments (placebo/caffeine) and measured the reinforcing value and intake of LED versus HED foods, intake at breakfast and throughout the day, appetite, and exercise responses. Study 1 identified increased frequency (5 days/week x 2 weeks) of aerobic exercise increased the reinforcing value and intake of LED foods. Study 2 identified a decrease in intake at a 3 mg/kg caffeine dose. Study 3 identified independent effects of caffeine or exercise on eating behavior. Portions of LED food earned was greater after 2 weeks of caffeine exposure. Intake and rate of intake increased after 2 weeks of exercise. Caffeine impaired exercise performance for overweight/obese. Hunger was greater and increased after 2 weeks caffeine without exercise. There were no combined effects of caffeine and short-term exercise on intake in the laboratory or under free living conditions. These finding suggest signals from exercise and caffeine on eating behavior may compete with each other or the effects may be too transient or too weak to be consistently replicated. More studies are needed to further elucidate the expected acute and chronic effects of caffeine and exercise, independently and combined, on eating behavior.