Participants are aware of both the scheduled time and the length of the next meal.

Resting-state and task-based heart rate, measured with a three-point electrocardiogram (ECG)

Resting-state and task-based heart-rate variability measured with a three-point electrocardiogram (ECG). Respiratory activity will also be recorded using a breathing belt to correct for breathing-related artifacts.

Resting-state and task-based skin conductance measured with two electrodermal activity electrodes placed on the fingers of the non-dominant hand.

Subjective stress levels are measured on a semi-continous scale from 1 (not at all) to 100 (extremely) repeatedly during each visit to assess stress responses to perceived food availability. Higher scores indicate greater stress.

Subjective hunger levels are measured on a semi-continous scale from 1 (not at all) to 100 (extremely) repeatedly during each visit to assess changes in subjective hunger ratings in response to perceived food availability. Higher scores indicate greater hunger.

Subjective fullness levels are measured on a semi-continous scale from 1 (not at all) to 100 (extremely) repeatedly during each visit to assess changes in subjective fullness ratings in response to perceived food availability. Higher scores indicate greater fullness.

Subjective satiety levels are measured on a semi-continous scale from 1 (not at all) to 100 (extremely) repeatedly during each visit to assess changes in subjective satiety ratings in response to perceived food availability. Higher scores indicate greater satiation.

Subjective cravings for sweet, salty, and fatty foods are measured on a semi-continous scale from 1 (not at all) to 100 (extremely) repeatedly during each visit to assess changes in subjective food craving ratings in response to perceived food availability. Higher scores indicate stronger food craving.

Levels of different hormones (e.g., estradiol, progesteron, testosterone, ghrelin, leptin) will be measured via blood sampling.

Cortosol levels will be assessed multiple times throughout the visit as an objective measure of stress.

Levels of insulin will be measured multiple times throughout the visit via blood sampling.

Glucose levels will be measured multiple times throughout the visit via blood sampling.

Changes in food intake related to stress is assessed with the Salzburg Stress Eating Scale (SSES; Meule et al., 2018). Higher Scores indicate increased food intake in response to stress, while lower scores indicate reduced food intake when experiencing stress.

Reward-related behavioral activation and inhibition are assessed using the Behavioral Inhibition System/Behavioral Activation System questionnaire (BIS/BAS; Strobel et al., 2001). Participants respond on a four-point Likert scale: "strongly disagree," "disagree," "agree," and "strongly agree." Higher scores on the BIS scale indicate greater behavioral inhibition, while higher scores on the BAS scale reflect stronger behavioral activation.

Impulsivity is assessed using the Barratt Impulsiveness Scale (BIS; Meule et al., 2011). Participants respond using a four-point scale: "rarely," "occasionally," "often," and "almost always." Higher scores indicate greater impulsivity.

Mood is measured twice during each visit before and after the ad libitum meal using the Positive and Negative Affect Schedule (PANAS; Janke & Glöckner-Rist, 2014). Participants respond to 20 mood adjectives-10 reflecting positive affect and 10 reflecting negative affect-using a five-point scale: "not at all," "very slightly," "moderately," "quite a bit," and "extremely." Higher scores on the positive affect scale indicate stronger positive mood, while higher scores on the negative affect scale indicate stronger negative mood.

Emotion regulation is assessed using the Emotion Regulation Questionnaire (ERQ; Abler & Kessler, 2009), which captures individual differences in the use of two distinct strategies to regulate emotions (cognitive reappraisal and expressive suppression). Participants rate their agreement with each item on a seven-point Likert scale, ranging from "strongly disagree" to "strongly agree." Higher scores on each subscale indicate more frequent use of the corresponding regulation strategy.

Perceived stress is assessed using the Perceived Stress Scale (PSS-10; Schneider et al., 2020), which aptures the extent to which individuals perceive their lives as unpredictable, uncontrollable, and overwhelming over the past month. Participants respond to general statements using a five-point scale ranging from "never" to "very often." Higher scores indicate greater perceived stress.

State anxiety is assessed twice during each visit before and after the ad lib meal using the state version of the State-Trait Anxiety Inventory (STAI; Grimm, 2009); which captures the current intensity of anxiety as experienced at the moment of assessment. Response options include "almost never". "a little", "moderately", and "very much". Higher scores indicate higher levels of state anxiety.

Interoceptive awareness is assessed using the Multidimensional Assessment of Interoceptive Awareness (MAIA; Eggart et al., 2021). The questionnaire measures various aspects of the awareness of internal bodily sensations. Participants respond to statements using a six-point scale: "never," "very rarely," "rarely," "occasionally," "frequently," and "always." Higher scores reflect greater awareness of bodily sensations.

Participants will rate their subjective loss of control over eating during the ad lib buffet task. Higher values indicate greater loss of control.

Depressive mood is assessed using the German version of the Beck Depression Inventory (BDI; Kühner et al., 2007). The questionnaire measures the severity of depressive symptoms experienced over the past two weeks. Higher total scores indicate more pronounced depressive symptomatology.

Body image is assessed using the Body Shape Questionnaire (BSQ; Pook et al., 2008), which measures concerns related to body shape commonly associated with eating disorders. Participants rate how frequently they experience body-related thoughts and feelings. Higher scores indicate greater body shape concern.

Food cravings are measured using the trait version of the Food Cravings Questionnaire (FCQ-T; Meule et al., 2012). Responses are given on a six-point scale from "never/not applicable" to "always," with higher scores indicating more frequent and intense cravings.

Dietary patterns are assessed using a food frequency questionnaire (Haftenberger et al., 2018), which captures the frequency and quantity of consumption across various foods and food groups over the past month. Participants indicate how often they consumed specific items and in which quantity, allowing for an overview of habitual dietary intake and eating patterns.

Intuitive eating is assessed using the Intuitive Eating Scale-2 (van Dyck et al., 2019), which evaluates individuals' tendency to rely on physical hunger and satiety cues to guide decisions about when, what, and how much to eat. Participants respond on a five-point scale ranging from "strongly disagree" to "strongly agree." Higher scores reflect a greater inclination toward intuitive eating behaviors.

Food insecurity status is assessed using the Food Insecurity Experience Scale (FIES; Depa et al., 2018), which evaluates individuals' access to food by addressing factors such as financial constraints, availability, and dietary quality. Response options include "yes," "no," "refused," and "don't know." Higher scores reflect greater severity of food insecurity.

Restrained eating is assessed using the "Cognitive Restraint of Eating" subscale from the Three-Factor Eating Questionnaire (TFEQ; Pudel & Westenhöfer, 1989). The subscale includes both true/false items and statements rated on a four-point Likert scale ranging from 1 ("always") to 4 ("never"). Higher total scores indicate greater cognitive restraint in eating behavior.

Eating motives will be assessed using the Eating Motives Survey (TEMS; Renner et al., 2012). Items are rated on a 7-point Likert scale, ranging from "never" to "always". Higher scores on TEMS subscales indicate a greater reliance on those eating motives when making food or eating choices.

Family climate is measured using the Familien Klima Skale (FKS; Roth, 2003). Items are rated on a 5-point Likert scale ranging from 1) "does not apply at all," 2) "applies little," 3) "applies moderately," 4) "applies predominantly," to 5) "applies almost completely." Higher total scores indicate a better family climate.

Attachment styles will be assessed using the Adult Attachment Scale (AAS; Schmidt et al., 2004). Items are rated on a five-point Likert scale ranging from "not at all true" to "exactly true." Higher scores on each subscale indicate a stronger endorsement of the corresponding attachment dimension. The subscales/attachment styles assessed are secure, avidant, anxious.

To assess the relationship between the gut microbiome and participants' food intake during the ad libitum meal, fecal samples will be collected prior to the first visit, during the observational phase in which participants record their habitual dietary intake.