Hormonal Control of Energy and Macronutrient Intake in Obesity (MEMORY)

The overall aim of the MEMORY study is to examine the concept of 'food memory' - how specific macronutrient compositions influence subsequent food preference and intake, and whether this differs across the BMI range from normal weight to obesity.

45 people (age 18-45 years old) with normal weight (BMI between 18.5-24.9 kg/m\^2, n=15), overweight (BMI between 25-29.9 kg/m\^2, n=15), and obesity (BMI above 30 kg/m\^2, n=15) will participate in this randomized cross-over study. Participants will complete one screening visit and two test visits.

During their test visits participants will be served a liquid meal consisting of either carbohydrate (sucrose) or protein (whey protein) diluted in water and sugar-free cordial mix for flavor. Participants will be served either carbohydrate or protein at their first visit and the opposite at their second visit in random order. The test visits will include clinical assessment (body weight, body composition, and blood pressure); Blood samples; Visual analogue scales for assessment of subjective appetite; Ad libitum buffet for assessment of energy intake. Participants will complete the Steno Biometric Food Preference Task (SBFPT), a computerized task measuring food choice, explicit liking, and implicit and explicit wanting with concomitant biometric measurements.

Time: -60 minutes (fasting), 0 minutes (liquid test meal), 150 minutes (ad libitum test buffet).

Descriptive data will be collected at the screening visit and will include body weight (kg); BMI, kg/m\^2; Fasting blood samples; Urine sample (future research); Adipose tissue biopsy (future research). Participants will also answer questionnaires regarding Socioeconomic status (SES), Control over eating (CoEQ), Health and wellbeing (SF-36), physical activity (international physical activity ((IPAQ)), and chronotype (morningsness/eveningsness ((MEQ)).

The specific research aims are:

1. To investigate whether intake of high-sucrose or high-protein affects subsequent food sensory-specific preference and different food intake from an ad libitum buffet, and whether this differs between individuals across the BMI range from normal weight to obesity.
2. To investigate whether the plasma FGF21 and glucagon responses:

   1. Differ between the above-mentioned macronutrient compositions,
   2. Are associated to subsequent food sensory-specific preference and macronutrient intake from an ad libitum buffet, and
   3. Differ between individuals across the BMI range from normal weight to obesity.
3. To investigate whether the postprandial responses of well-known appetite-related hormones, as well as unexplored metabolites and proteins:

   1. Differ between the above-mentioned macronutrient compositions,
   2. Are associated to subsequent food sensory-specific preference and macronutrient intake from an ad libitum buffet, and
   3. Differ between individuals across the BMI range from normal weight.
4. To identify new biomarkers facilitating patient stratification and optimize future treatment of obesity.

Eligibility Criteria:
Inclusion Criteria:

* Age 18-45 years
* For women: Regular menstruation
* BMI-range 18.5-39.9 kg/m\^2

Exclusion Criteria:

* Not able or willing to eat or drink the test meals because of e.g., allergy or intolerance
* Daily smoking
* For women: Pregnancy / planned pregnancy (within the study period) / lactating
* Self-reported history of an eating disorder
* Self-reported weight change (kg) within two months prior to inclusion
* HbA1c ≥48 mmol/mol
* Treatment with antidepressants
* Alcohol/drug abuse or in treatment with disulfiram (antabus) at time of inclusion
* Uncontrolled medical issues including but not limited to cardiovascular pulmonary, rheumatologic, hematologic, oncologic, infectious, gastrointestinal, or psychiatric disease; diabetes or other endocrine disease; immunosuppression
* Current treatment with medication which significantly affect appetite or energy balance (e.g., GLP-1 receptor agonists)
* Bariatric surgery
* Unable to understand the informed consent and the study procedures
* Concomitant participation in intervention studies
* Participant's withdrawal of the informed consent
* Other safety concerns - judged by the investigator