The Interaction Between Resting Metabolic Rate, Physical Activity and Thyroid Hormone in Females

Subjects will be asked to fast overnight and weight will be measured using a calibrated Seca body weight scale first thing in the morning on subjects wearing light clothes and no shoes.

Measured by seca 217 stable stadiometer. Subjects wearing no shoes.

Waist and Hip circumferences will be measured using a whole body laser scanner.

Fat mass will be measured by Magnetic Resonance Imaging (Shanghai united imaging, uMR 790 ) or DXA (Hologic).

Fat free mass will be measured by Bioimpedance Analysis (Tanita, MC-980) or DXA (Hologic).

Bone mass will be measured by DXA (Hologic).

Resting energy expenditure will be measured using indirect calorimetry via a respiratory hood system (Cosmed). The subject attends the lab after an overnight fast. The person lies down on a flatbed and the hood is placed over their head. Metabolic rates (oxygen consumption and CO2 production) are monitored for 30 minutes. Calorimeters will be assessed with a turbine test to ensure the accuracy of measurements. Validation via an alcohol burn will be performed monthly.

Physical activity of the participants will be recorded using GT3X accelerometer worn near the hip for a consecutive period of 14 days. The monitor should not be worn while bathing or swimming. The first day is discarded along with any day where the wear time is less than 10 hours. For a valid measure, the goal is to get at least 2 weekday and 2 weekend days.

Nurses will collect the blood samples on day 1. Levels of circulating thyroid hormones will be measured using radio immunoassay.

The whole room calorimeter/metabolic chamber (OMNICAL, Maastricht instrument) will be used to measure resting metabolic rate. The metabolic chamber is a sealed room with a continuous gas supply (CO2- 0.80×10-2, O2 -18.00×10-2), providing subjects with 24-hour energy expenditure data. The total energy expenditure of the subjects in MJ/day was plotted against time in 30-minute intervals over 24 hours. The lowest and most stable energy expenditure during sleep time was considered the RMR of the subjects, which occurred from 2:00 am to 5:00 am.

Total energy expenditure (TEE) will be measured using the DLW method. Urine samples from all participants in the DLW subset will be stored at -20 oC and analyzed in the laboratory of Dr. John Speakman at the Shenzhen Institute of Advanced Technology, Chinese Academy of sciences. Isotopes will be measured in a benchtop near-infrared isotope gas analyzer, and mean CO2 production will be calculated from isotope ratios using the recently derived equation (Speakman et al 2021: Cell reports medicine). TEE will then be calculated using mean CO2 production using the Weir equation.

Total energy expenditure will be measured using the whole room calorimeter / metabolic chamber (OMNICAL, Maastricht instrument). The metabolic chamber is a sealed room with a continuous gas supply (CO2- 0.80×10-2, O2 -18.00×10-2), providing subjects with 24-hour energy expenditure data. The total energy expenditure was calculated by averaging the chamber's gaseous exchange using a 24-hour time window between 11.30 am and the next day around 3.00 pm.