Persistent low body weight in humans is associated with higher mitochondrial activity in white adipose tissue.

Background: Constitutional thinness (CT) is a state of low but stable body weight (BMI ≤18 kg/m2). CT subjects have normal-range hormonal profiles and food intake but exhibit resistance to weight gain despite living in the modern world's obesogenic environment.

Objective: The goal of this study is to identify molecular mechanisms underlying this protective phenotype against weight gain.

Rational and design of an overfeeding protocol in constitutional thinness: Understanding the physiology, metabolism and genetic background of resistance to weight gain.

Background: Constitutional thinness (CT) is a natural state of underweight (13-17.5kg/m) without the presence of any eating disorders and abnormal hormonal profile, and with preserved menses in women. We previously conducted a four-week fat overfeeding study showing weight gain resistance in CT women and one of our main results was the identification of an energy gap: a positive energy balance (higher energy intake than energy expenditure).