Evaluation of Methods for Measuring Food Reward and Food-related Behavior in Healthy Individuals

Measured using eye tracking in response to looking at food pictures during the computerized Leeds Food Preference Questionnaire.

Includes the following parameters: Gaze: Time spent (ms and %) and revisits (n); and fixations: Time to first fixation (ms), time spent (ms and %), fixation count (n), first fixation duration (ms), average fixation duration (ms). Distance to screen (mm), and gaze direction bias (ratio) which is calculated as the number of trials in which the first fixation was directed to a food image as a proportion to all trials. A bias score ˃0.5 indicates attention towards one food image, a bias score equal to 0.5 indicates no bias, and a bias score <0.5 indicates attention towards the other food images.

Measured as galvanic skin response (changes in conductivity of the skin) in response to looking at food pictures during the computerized Leeds Food Preference Questionnaire.

Includes the following parameters: Presence of a peak (yes/no), peak count (n), peaks/min, peak (ms), peak amplitude (μS), peak onset (ms), peak offset (ms), duration (ms), tonic signal (μS).

The presence of a peak, the magnitude of the peak as well as the duration of the peak are measures of arousal (includes all the parameters listed above). The greater the response the higher the arousal.

Emotions including anger, sadness, disgust, joy, surprise, fear, contempt as well as facial expression metrics (actions units) are determined by facial expression analysis using computer-vision algorithms (AFFDEX) in response to looking at food pictures during the computerized Leeds Food Preference Questionnaire.

Results represent the probability the emotions and facial expression metrics were expressed (range: 0-100; 0=it was not expressed, 100=it was expressed, 50=50% likelihood that it was expressed).

Food choice of food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined from the computerized Leeds Food Preference Questionnaire. Food choice is determined based on frequency of selection made within each food category. The scores range from 0-48 i.e. 0 = foods within a specific food category have not been selected at all to 48 = foods within a specific food category have been selected 48 times.

Reaction time during forced food choice of food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined from the computerized Leeds Food Preference Questionnaire.

Implicit wanting of food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined from the computerized Leeds Food Preference Questionnaire. Implicit wanting is assessed based on food choice and response time for selected and non-selected food items as well as mean response time (a frequency-weighted algorithm).

In this frequency-weighted algorithm a positive score indicates a more rapid preference for a food type over another food type and a negative score indicates the opposite. A score of zero indicates that food types are equally preferred. The frequency weighted algorithm is used so the implicit wanting score is influenced by both selection (positively contributing to the score) and non-selection (negatively contributing to the score) of food type. Scores for implicit wanting typically range from -100-100 (due to reaction time there is no fixed min-max value)

Explicit liking of 16 food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined from the computerized Leeds Food Preference Questionnaire. Explicit liking is rated using visual analogue scales and the range is 0-100. Each end represents the extremes e.g. Question: "how pleasant would it be to taste this food right now?" Answer: "not at all" (rated 0 on the 0-100 scale) to "extremely" (rated 100 on the 0-100 scale).

Explicit wanting of 16 food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined from the computerized Leeds Food Preference Questionnaire. Explicit wanting is rated using visual analogue scales and the range is 0-100. Each end represents the extremes e.g. Question: "how much do you want some of this food now?" Answer: "not at all" (rated 0 on the 0-100 scale) to "extremely" (rated 100 on the 0-100 scale).

Rated using visual analogue scales and includes sensations of: Hunger, fullness, satiety, prospective food consumption, wellbeing, nausea, thirst, desire to eat meat, salty, and sweet. The scale range is 0-100 and each end represent the extremes e.g. hunger rating: "I am not hungry at all" to "I have never been this hungry before".

Body weight is measured on a digital scale

Calculated from body weight (kg) and height (m)

Measured by Dual-energy X-ray Absorptiometry

Measured by Dual-energy X-ray Absorptiometry

Measured by Dual-energy X-ray Absorptiometry

Measured using tape measure

Measured using tape measure

Measured under resting and fasting conditions

Measured under resting and fasting conditions

Measured under resting and fasting conditions

Hemoglobin A1c

Assessed using the Pittsburgh Sleep Quality Index. The questionnaire covers sleep quality and sleep disturbances over the preceding month and includes 19 individual items that generate seven scores weighted on a 0-3 scale. The sum of the component scores yields a total score of 0-21, and the higher the score, the poorer the sleep quality. The questionnaire also covers bedtime (hh:mm), sleep onset latency (minutes/night), wake-up (hh:mm); sleep duration (hours and minutes per night).

Assessed using the Epworth Sleepiness Scale. The questionnaire describes eight different situations of everyday life, and participants are asked to rate how likely they would doze off or fall asleep in each situation on a 0-3 scale. The sum of the scores yields a total score of 0-24, with higher scores indicative of greater daytime sleepiness.

Assessed using the Short Form Health Survey (SF-36). The questionnaire covers self-reported health status and the response format is a Likert-type scale e.g. question regarding overall health from 1=excellent to 5=poor and binary scales (yes/no) e.g. "difficulties performing daily tasks".

Assessed using the Recent Physical Activity Questionnaire. The questionnaire covers physical activity during work and in transport and leisure-time domains. The response format is a Likert-type scale e.g. 1=never and 5=always and participants are also asked about distance to work and typical mode of transportation. The time spent (minutes/day) on different modes of transportation or work-related or leisure-time physical activities and exercise as well as intensity (sedentary, light, moderate, vigorous) of the activities can be calculated.

Assessed using the Munich Chronotype Questionnaire. The primary outcome is sleep midpoint (hh:mm) calculated based on participants' registration of habitual bedtime (hh:mm), sleep onset (hh:mm), sleep onset latency (minutes), wake-up (hh:mm), time from wake-up to out of bed (minutes). The questionnaire also covers use of sleep medicine and intake of alcohol and coffee/tea (units/day, units/ week, units/months), type of transportation to work (car/bus/train, walking/bicycling or work from home) and duration of transportation (minutes/day).

Assessed using the Night Eating Questionnaire. The questionnaire covers hunger and craving for foods at different times during the day and night. The response format is a Likert-type scale ranging from e.g. 0=not at all to 4=very much.

Assessed using the Dutch Eating Behavior Questionnaire. The questionnaire consists of 33 questions and assess restrained (10 items), emotional (13 item), and external (10 items) eating behavior. The response format is a Likert-type scale ranging from 1=never to 5= very often. The greater the total score within each category the greater degree of e.g. dietary restraint.

Assessed using the Control Over Eating Questionnaire. Control of eating and the degree of food cravings are assessed using the 21-item questionnaire which includes questions related to food cravings, control of eating, appetite and overall mood. Based on the previous 7 days, participants are asked to rate 20 questions on a 100 mm visual analogue scale (VAS). One question is open-ended. The VAS range is 0-100 and each end represent the extremes e.g. "how difficult is it to control eating": "Not difficult at all" to "It has never been more difficult".

Assessed using a questionnaire assessing self-reported educational level (categorical), main occupation (categorical), civil status (categorical), ethnicity (categorical), living arrangement (categorical), children (n), personal income (DKK), household income (DKK), sex (male/female), and age (years).

Total energy intake during an ad libitum buffet meal provided after all basal assessments

Energy intake from different food categories (high fat-savoury, high fat-sweet, low fat-savoury, low fat-sweet) during an ad libitum buffet meal provided after all basal assessments

Explicit liking of 8 food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined during an ad libitum buffet meal provided after all basal assessments. Explicit liking is rated using visual analogue scales and the range is 0-100. Each end represents the extremes. Question: "how pleasant is the taste of the food right now?" Answer: "not pleasant at all" (rated 0 on the 0-100 scale) to "very pleasant" (rated 100 on the 0-100 scale).

Explicit wanting of 8 food items from four combined food categories (high-fat savoury, high-fat sweet, low-fat savoury and low-fat sweet foods) examined during ad libitum buffet meal provided after all basal assessments. Explicit wanting is rated using visual analogue scales and the range is 0-100. Each end represents the extremes. Question: "How much more do you think you can eat of the food right now?" Answer: "nothing at all" (rated 0 on the 0-100 scale) to "very much" (rated 100 on the 0-100 scale).