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Study Design

Screening visit (Visit 1) Participants will be asked to complete a health screening questionnaire. Only those in generally good health will be enrolled. Following this, weight and height will be measured, and the body mass index (BMI) will be determined. Finally, participants will complete the International Physical Activity Questionnaire and food preferences questionnaire to ensure they like the foods provided in the study. Moreover, they will be provided with a 24-hour food diary to complete 24 hours before the first experimental trial, along with a set of scales to help them measure and record all items. Participants will be instructed to follow this food diary in the 24 hours before the second trial, ensuring that the food and drink consumed in the 24 hours before each experimental trial are similar.

Experimental trials (Visits 2 and 3) In the 24 hours prior to the experimental trial, participants will complete a 24-hour food diary where they record all food and beverages. With this diary, participants will describe all drinks and food consumed using household measures (e.g. teaspoon, cup). They will be asked to record a detailed description of food and/or drink intake, time and place of consumption. They will also record details on food brands, preparation and cooking methods. Portion sizes should be estimated using household measures or natural unit sizes (e.g., slices of bread). Food diaries and an electronic kitchen scale (Salter Housewares Ltd., Tonbridge, UK) will be provided to subjects, and they will be shown how to use the scales and how to record. They will follow this food diary in the 24 hours prior to the second visit to ensure they replicate their food and drink consumption in the 24 hours before each experimental trial.

Participants will arrive at the laboratory before both experimental trials at approximately 08:30, having fasted for at least 12 hours (participants instructed not to eat or drink after 20:30 from the previous night, except water). They will be weighed and then, at approximately 09:30. They will consume a standardised breakfast comprising porridge oats, full-fat milk, croissants, butter, jam and orange juice, which they will have 30 minutes to consume. Participants will then rest in the metabolic research unit for the remaining 3.5 hours of the trial (5-hour visit in total), completing study questionnaires where necessary. They will be able to consume water ad libitum and will be able to bring laptops/tablets and books.

During the experimental trial, participants will complete the weekly Visual Analogue Scale (wVAS), the Three Factor Eating Questionnaire (TFEQ) and the Intuitive Eating Scale-2 (IES-2) in the fasted state before the breakfast meal; while in the second trial, participants will be asked to complete these 90 minutes after the administration of the breakfast meal. In a randomised counter-balanced design, half of the participants will complete these scales in the fasted state first, whilst the other half will complete these scales after the breakfast meal first.

Throughout both experimental trials, participants will be periodically asked to complete measures of instantaneous appetite and food cravings. Instantaneous appetite ratings will be measured through the instantaneous Visual Analogue Scale (iVAS). These will examine various appetite constructs: hunger, satisfaction, fullness, prospective food consumption and desire to eat. Participants will be asked to place a vertical mark on the horizontal line at a point corresponding to their feelings at that time (hence the term instantaneous appetite). Participants will complete iVAS first at approximately 09:00, just before the breakfast meal. Thereafter, iVAS will be administered every 60 minutes (five assessments in total).