Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans

This protocol quantifies the physiological significance of human brown adipose tissue activity by combining carbohydrate loading with indirect calorimetry and changes in supraclavicular temperature. This protocol does not expose participants to ionizing radiation. It detects changes in measured supraclavicular temperature, combined with core temperature and the temperature of a reference region.

On the day of the study, begin with measuring the height and weight of the participants. Ask the participants to lay down on a plinth. After 30 minutes, record their baseline parameters.

Following this, allow the participants to consume three carbohydrate drills of 90 grams each between zero to 15 minutes. After 45 minutes post-carbohydrate loading, allow the participants to ingest the 100 milligrams of caffeine treatment capsules. To perform indirect calorimetry, use a calibrated respiratory gas analyzer.

Fit the cold sterilized silicone mask equipped with a pre-sterilized non-rebreathing valve on the participant to deliver room air. Fix it on the participant's face with a mesh attachment and check for leaks. Ensure that the inspiratory and expiratory tubes are connected.

After sampling the expired gases, remove the mask to complete the additional measurements and measure the substrate oxidation rates as described in the text manuscript. After each round of expired gas measurements, use a glucometer to measure blood glucose levels. Direct a non-contact thermometer toward the center of the participant's forehead.

To perform infrared thermography, make the participants sit in an upright position looking straight ahead with their neck to chest region exposed. Position the thermal imaging camera on a tripod at neck level about one meter from the subject's face. After switching on the camera, adjust the focus by rotating the focus ring.

Point a laser pointer at the midline of the participant's neck. And click a picture. To analyze the infrared images, assess the surface temperatures of the thorax region containing brown adipose tissue by placing triangular regions of interest in the supraclavicular fossa and a circular region of interest on the sternum.

Consider the sternal area as the control reference point, as this area does not contain brown adipose tissue. Once the regions have have been cross-located, obtain the average and standard deviation of the temperature for each region using the software. The effects of caffeine intervention on the temperature measures of the core and supraclavicular fossa region are indicative of brown adipose tissue thermogenesis.

The intervention displayed a marked effect in the metabolic measures with the increase in the supraclavicular temperature and rapid lowering of blood glucose levels. These findings, combined with a lack of temperature changes in the core and reference region temperature, indicate brown adipose tissue thermogenesis. Increased energy expenditure resulted in decreased respiratory exchange ratio and coincidentally increased fat oxidation.

It's important to ensure that the room is kept at a stable temperature;the silicon mask is fitted properly;and the thermal imaging camera is at neck level, at least one meter away from the participant. It would be advisable to measure blood markers for insulin. The rapid return of blood glucose levels following the intervention suggests that the intervention itself may have improved insulin signaling.

This technique permits repeated measures analysis. This is something that cannot be done with PET imaging studies. The extent to which dietary ingredients and pharmacological agents can impact brown adipose tissue activity in humans can now be assessed in a safe, accessible way.