How Metabolism Affects Weight Loss and Gain

This observational study explores why some lean people struggle to gain weight while some obese people struggle to lose it, by measuring how the body uses energy under fasting conditions and after eating a specially designed low-protein meal. Using a technique called indirect calorimetry, researchers will identify whether individuals fall into 'thrifty' (energy-conserving) or 'spendthrift' (energy-expending) metabolic patterns. Eligible participants are either lean adults (BMI 18.5–22) reporting difficulty gaining weight, or obese adults (BMI over 30) reporting difficulty losing weight, without diabetes, significant heart disease, or gastrointestinal disorders. Participation involves two clinic visits including a 24-hour fast, a meal test, and various body and metabolic measurements. This summary was prepared to help patients understand the study in plain language.