Interindividual variability in perceived appetite and appetite-related hormone responses to eating and exercise in humans

As obesity rates continue to rise worldwide, scientific interest in the area of appetite regulation has increased in an attempt to identify strategies that can prevent energy overconsumption and body weight gain. Appetite regulation is complex and involves many different physiological and psychological factors, allowing for great interindividual variability. Recently, some studies assessing appetite and energy intake responses to meal or exercise interventions have shifted the focus on presenting findings exclusively as group means to assessing individual responses and exploring interindividual variability. However, important methodological limitations may have impaired the detection of true interindividual variability, and gold standard study design and statistical approaches that address these limitations have been recently suggested. Therefore, this thesis aimed to assess the reproducibility and quantify the interindividual variability in appetite responses to acute exercise and to a standardised meal, and to explore the influence of genetic, physiological and behavioural characteristics on fasting and postprandial appetite-related outcomes. To achieve this, a total of 145 healthy men and women were recruited into four experimental studies.The first experimental study (Chapter 4) demonstrated, using a replicated crossover design, that young men exhibited reproducible appetite responses after 60-min of fasted treadmill running at 70% peak oxygen uptake. True interindividual variability was observed in acylated ghrelin, total peptide YY (PYY) and perceived appetite responses over and above any random within-subject variability and measurement error, even after adjustment for individual baseline measurements. In the second experimental study (Chapter 5), the fat mass and obesity- associated gene (FTO) was not significantly associated with fasting or postprandial perceived appetite, acylated ghrelin, total PYY, insulin, glucose and leptin in healthy men and women, with or without the addition of physiological and behavioural covariates in the statistical models. While fasting leptin, glucose and insulin and postprandial insulin concentrations were associated with adiposity outcomes, the associations between fasting and postprandial acylated ghrelin, total PYY and general or abdominal adiposity were small. The third experimental study (Chapter 6) employed a replicated crossover design to demonstrate that the reproducibility of appetite responses to a standardised meal (5025 kJ) is generally good in healthy men. True interindividual variability was present in perceived appetite, acylated ghrelin, total PYY, insulin and glucose responses to the meal beyond any random within-isubject variation over time, but the magnitude of change in postprandial appetite responses was not influenced by the FTO gene. The final experimental study (Chapter 7) consisted of a pilot study which showed no significant association between brown adipose tissue activity assessed with thermal imaging, FTO genotype and fasting and postprandial acylated ghrelin, total PYY, insulin and glucose in healthy males.Collectively, these studies demonstrate that appetite responses to acute exercise and to eating are reproducible in healthy men, and true interindividual variability exist in these responses. However, the FTO genotype was not significantly associated with fasting and postprandial perceived appetite and appetite-related hormones, and further studies are warranted to investigate other individual characteristics that may moderate the observed interindividual variability. These findings highlight the importance of exploring individual differences in appetite responses in the context of the prevention and/or management of obesity.</div

Strength Training Prior to Endurance Exercise: Impact on the Neuromuscular System, Endurance Performance and Cardiorespiratory Responses

This study aimed to investigate the acute effects of two strength-training protocols on the neuromuscular and cardiorespiratory responses during endurance exercise. Thirteen young males (23.2 ± 1.6 years old) participated in this study. The hypertrophic strength-training protocol was composed of 6 sets of 8 squats at 75% of maximal dynamic strength. The plyometric strength-training protocol was composed of 6 sets of 8 jumps performed with the body weight as the workload. Endurance exercise was performed on a cycle ergometer at a power corresponding to the second ventilatory threshold until exhaustion. Before and after each protocol, a maximal voluntary contraction was performed, and the rate of force development and electromyographic parameters were assessed. After the hypertrophic strength-training and plyometric strength-training protocol, significant decreases were observed in the maximal voluntary contraction and rate of force development, whereas no changes were observed in the electromyographic parameters. Oxygen uptake and a heart rate during endurance exercise were not significantly different among the protocols. However, the time-to-exhaustion was significantly higher during endurance exercise alone than when performed after hypertrophic strength-training or plyometric strength-training (p <0.05). These results suggest that endurance performance may be impaired when preceded by strength-training, with no oxygen uptake or heart rate changes during the exercise

Disordered eating behaviors and body image in male athletes

Objective: To identify disordered eating behaviors and body image dissatisfaction, as well as their relationship to body fat (BF), among male athletes in high risk sports for eating disorders. Methods: One hundred and fifty-six male athletes were divided into the following categories: weight-class sports, sports where leanness improves performance, and sports with aesthetic ideals. BF was assessed and three questionnaires were used: the Eating Attitudes Test; the Bulimic Investigatory Test, Edinburgh; the Body Shape Questionnaire. Results: Disordered eating behaviors and body image dissatisfaction were found in 43 (27.6%) and 23 athletes (14.7%), respectively, and an association was detected between the two variables (p < 0.001). Athletes with and without disordered eating behaviors did not differ in %BF (11.0±5.2% and 9.8±4.0%, respectively; p = 0.106). However, athletes with body image dissatisfaction had higher %BF than those who were satisfied (12.6±5.9% and 9.7±3.9%, respectively; p = 0.034). There were no differences in BF, frequency of disordered eating behaviors, and body image dissatisfaction between sports categories. Conclusion: Nearly one-quarter of athletes showed disordered eating behaviors, which was associated with body image dissatisfaction. Athletes with higher %BF were more likely to be dissatisfied with body image. There was no difference in eating behavior and body image between athletes from different sports categories