The Influence of Acute Continuous Exercise and Adiposity on Appetite Hormones and Neural Correlates of Visual Food Cues

Exercise increases energy expenditure and impacts appetite and energy intake. Some appetite-related hormones such as oxyntomodulin suppress appetite whilst other hormones such as ghrelin stimulate appetite. This study will investigate whether acute continuous walking/jogging influences these hormone concentrations, and whether exercise-induced changes in the hormones correlate with perceptions of appetite, nutritional intake and brain activity in individuals varying in weight status.

Single bouts of exercise transiently suppress appetite and the orexigenic gut hormone acylated ghrelin and increase anorexigenic gut hormone concentrations including peptide YY (PYY) and glucagon-like peptide-1 (GLP-1). These changes occur without stimulating compensatory increases in appetite and energy intake on the day of exercise resulting in a short-term energy deficit. Oxyntomodulin is another gut-derived hormone that suppresses appetite and increases energy expenditure but the influence of acute exercise on oxyntomodulin concentrations in individuals varying in adiposity status has not been investigated. This study will investigate whether acute continuous walking/jogging impacts circulating oxyntomodulin concentrations in individuals who are lean or living with overweight or obesity. The influence of exercise and adiposity on other hormonal, subjective, sensory and neural correlates of appetite will also be explored.

This study is a cross-over design consisting of four visits: a pre-visit, two main trial visits (exercise and control) and a magnetic resonance imaging (MRI) visit. Participants will undertake a preliminary measures visit (pre-visit) to confirm eligibility, complete questionnaires assessing their health, habitual physical activity and eating behaviours, undergo standard anthropometric measurements (height, weight, and hip/waist circumference) and treadmill exercise tests to determine their peak oxygen uptake.

Main trials will be separated by at least seven days for male participants, whereas female participants will complete the two main trials in the follicular phase (the first seven days) of the menstrual cycle. Participants will arrive at the laboratory after fasting overnight for at least 10 hours (plain water is permitted). Participants will then complete assessments of height, weight and either bioelectrical impedance analysis (main trial 1) or air displacement plethysmography (BOD POD®) (main trial 2). A venous cannula will be inserted for the collection of venous blood samples at 30-minute intervals (0 hours \[08:30\], 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours and 4 hours). Subjective appetite ratings will be measured at 30-minute intervals (0 hours \[08:30\], 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours and 4.5 hours). Participants will complete the Burghart ODOFIN Sniffin' Sticks smell test and the Burghart ODOFIN taste strips test at three time points during the trials (0 hours \[08:30\], 1.5 hours and 4 hours). Participants will rest for the duration of the trials except for performing 1 hour of treadmill exercise (walking/jogging) at 60% of their peak oxygen uptake (calculated from the pre-visit) between 0.5 to 1.5 hours (09:00-10:00) in the exercise trial. Expired air samples will be collected during exercise and for 30 minutes during the rest trial to calculate net energy expenditure and substrate oxidation. At 2.5 hours (11:00), an ad libitum lunch consisting of a homogeneous meal containing pasta, tomato sauce, and olive oil (72% carbohydrate, 12% protein, 16% fat, 6.5 kJ per gram of food) will be provided for 30 minutes (until 3 hours).

The MRI visit will take place after an overnight fast of at least 10 hours and will involve a 45 minute scanning protocol. Structural MRI and functional MRI (fMRI) scans will be performed on a GE 3.0 T Discovery MR750w scanner using a 32 channel head coil. Two fMRI scans will be performed (1) during the presentation of food and non-food cues and (2) for an equivalent duration whilst participants are not looking at food and non-food cues.

Eligibility Criteria:
Inclusion Criteria:

* Body mass index (BMI) between 18.5 - 24.9 kg/m2 and a waist circumference of ≤ 88 cm for women, and ≤ 102 cm for men or a BMI between 25 - 40 kg/m2 and a waist circumference of \> 88 cm for women, and \> 102 cm for men. BMI and waist circumference thresholds vary amongst ethnicities. People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background are prone to central adiposity and their cardiometabolic risk occurs at a lower BMI. Therefore, the following BMI and waist circumference thresholds will be applied for people of South Asian, other Asian, Black African and African-Caribbean ethnicity: (1) BMI 18.5 kg/m2 to 23 kg/m2 and waist circumference of \< 90 cm for men and \< 80 cm for women; (2) BMI 23.1 kg/m2 to 40 kg/m2 and waist circumference of ≥ 90 cm for men and ≥ 80 cm for women.
* Normally consumes three meals a day
* Able to walk continuously for 1 hour on a treadmill
* Weight stable for 3 months (\< 3kg change in weight)
* Regular menstrual cycle for the last 6 months (people taking the combined contraceptive pill are eligible for the study)
* Able to undergo a 45-minute MRI scan

Exclusion Criteria:

* Smokers (vaping is considered smoking in this study)
* Known medical conditions (e.g. diabetes, heart condition)
* Taking any medication which may affect the study outcomes (e.g. liraglutide, semaglutide, insulin, steroids, anti-psychotics)
* Clinically diagnosed eating disorder
* Previous bariatric surgery (e.g. gastric bypass, gastric band, sleeve gastrectomy)
* Food allergies or intolerances, or severe dislikes to study foods
* Pregnant or breastfeeding
* Have recently donated blood (within eight weeks of visits 2 and 3).