Energy Metabolism and Eating Behavior in Underweight and Normal-weight Individuals

Metabolic Flexibility, Eating Behavior and Adipose Tissue Expandability: Role of This Triad in the Propensity to Human Obesity

This study evaluates eating behavior and metabolic responses following consumption of a high-fat high-energy meal in healthy underweight and normal-weight adults. The primary research question is: Do healthy underweight individuals exhibit different eating and metabolic responses compared with normal-weight adults following consumption of a high-fat high-energy meal?

Healthy underweight individuals have a body mass index below the normal range in the absence of a medical condition, food aversion, food insecurity, or evidence of unusually high levels of physical activity. Although the environmental factors contributing to their lower body mass index are not fully understood, these individuals may represent a phenotype resistant to the obesogenic environment. If so, the biological mechanisms underlying this resistance remain poorly understood. Such mechanisms must ultimately influence energy expenditure, energy intake, or both.

This study will compare metabolic responses and eating behavior during fasting and following consumption of a high-fat, high-energy meal in healthy underweight and normal-weight adults. Eating behavior will be assessed through measures of food liking, subjective appetite perceptions, and ad libitum energy intake. Metabolic responses will include assessments of energy expenditure, substrate oxidation, and circulating metabolites and hormones.

We hypothesize that healthy underweight individuals will exhibit greater postprandial satiety and lower ad libitum energy intake than normal-weight adults.

Inclusion criteria:

• Men or women
• Age 18-25 years
• Stable body weight during the previous 6 months (±2 kg)
• Healthy according to medical history and laboratory assessments
• BMI: 15.0-<18.5 kg/m2 or 20.0-<25.0 kg/m2

Exclusion criteria:

• Pregnancy or lactation
• Athletes or individuals engaged in high levels of physical activity, including those participating in competitive sports, structured endurance training, or physically demanding occupations.
• Cardiovascular, liver, kidney, thyroid, or other chronic diseases requiring medical treatment
• Conditions affecting energy metabolism or eating behavior
• Smoking or alcohol abuse
• Phobia or vasovagal response associated with blood draws
• Intolerance or allergy to peanuts, chocolate, eggs, or gluten
• Irregular menstrual cycles (>3 months without menstruation)
• Current or previous diagnosis of eating disorders
• Psychiatric disorders requiring antidepressant or psychotropic treatment

Additional criterion for healthy underweight participants:

• Absence of food insecurity
• Low body weight not attributable to eating disorders or exercise-related behaviors