In the last decade growing interest has been directed to the BAT due to its potential as a therapeutic target to treat obesity. The most remarkable aspect is represented by the BAT plasticity present in adults. The ability to recruit beige adipocytes within WAT has further added to the focus on BAT, or more strictly on UCP1-dependent adipocyte thermogenesis, as a therapeutic route in obesity. The best-known and effective inducer of brown adipogenesis and function is norepinephrine.. Of particular interest from the perspective of novel therapeutics for obesity and diabetes, there have now been identified additional specific-secreted signaling molecules that trigger brown adipocyte development, including nodal, wingless, sirtuins, ketone bodies and members of the fibroblast growth factor (FGF). The objective of the present study is to explore the role of BAT activation in response to an oral fat tolerance test in subjects with obesity through the combination of three relevant methods: 1. the use of infrared thermography to identify and quantify BAT activation; 2. the use of indirect calorimetry in order to measure energy expenditure in response to meal-related BAT activation; 3. the measurement of heart rate variability as a proxy of the sympathetic system activation, which is an important mediator of BAT function and activity. Participants will be recruited among subjects referring to the Section of Medical Pathophysiology, Food Science and Endocrinology - Department of Experimental Medicine, ¿Sapienza¿ University of Rome, Italy, over a 1-year period. Primary outcome measure: Infrared thermography- related temperature changes during the oral fat load. Secondary outcome measures: Energy expenditure.Thermic effect of food (Indirect calorimetry). Postprandial lipids trajectories. Fasting and postprandial substrate oxidation (AUC CHO and AUC FAT oxidation: mg/min; time point respiratory quotient))Heart rate variability changes during the test meal.
In the last years novel methodologies have been developed in order to explore BAT activation, based on infrared thermography. This novel method is non-invasive, cheap and quick, requires very little equipment, and it especially avoid patient¿s/subject¿s exposure to x-rays.
The principle of infrared thermography is the process of constructing an image of an object's temperature by first measuring the emission of infrared radiation, then converting that radiometric data to a temperature and, finally, displaying the temperature data as an image. The infrared radiation emitted is related to the temperature of the body with long-wavelength IR (8¿15¿m) emitted by objects whose temperature is between -80°C and 89°C, including the human body.
IRT offers a complementary detection method for BAT activity and can overcome some of the drawbacks of PET/CT. The non-invasive nature of thermal imaging and its avoidance of ionizing radiation make it highly suitable for BAT measurements in healthy cohorts or children and young people. The flexible and non-harmful nature of IRT make serial measurements of large numbers of individuals become feasible and ethical. In contrast to PET/CT, IRT measures heat directly which is the key outcome of thermogenesis. The practical and ethical freedoms of IRT compared to PET/CT thereby confer the ability to create large datasets which will provide increased confidence in results as well as allow others to check that results are reproducible.