Introduction: Constitutional thinness (CT) is a rare condition of natural low body weight, with normal menstruation, no fear of weight gain and no hormonal abnormalities except for an anorexigenic hormonal profile. CT can be considered as the opposite of obesity and its resistance to weight loss. Therefore, we hypothesised they would have a resistance to weight gain.
Methods: 10 female Controls (BMI 18.525 kg/m2) and 10 CT women (BMI<17.5 kg/m2) underwent a 4-week fat overfeeding (700 kcal) intervention. Body weight, food intake, body composition, energy expenditure and the profile of appetite regulatory hormones after test meals were monitored prior to and after dietary intervention.
Results: After one month of fat overfeeding, the mean body weight remained the same in the CT group (−0.300 kg, P=0.258 vs baseline) showing a resistance to weight gain, whereas it normally significantly increased in the control group (+1.3 kg, P=0.0248). After one month ad libitum food intake, the CT group body weight significantly dropped down (−0.850 kg, P=0.0245 vs the end of the overfeeding period), showing a rapid escape of the body weight gain, whereas the control group maintained its body weight gain (+1.5 kg, P=0.02 vs baseline). Resting energy expenditure significantly increased in the CT group only (P=0.0307). In the CT group, post meal PYY plasma levels (P=0.008) and post meal exposure time to GLP-1 significantly increased (P=0.04), emphasising the baseline anorexigenic profile. Conversely, in the control group, total and acylated ghrelin plasma levels increased significantly (P=0.016 and P=0.028 respectively) in an orexigenic profile.
Conclusion: This data is the first to demonstrate a resistance to weight gain in constitutional thinness population in response to 4-week fat overfeeding, associated with an increase in resting energy expenditure and an emphasised anorexigenic hormonal profile.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This work was supported, however funding details unavailable.