JMIR Publications

ABSTRACT

Background:

Long-term body weight is regulated by the balance between energy intake and energy expenditure (EE). Although weight stability requires energy balance, achieving and maintaining such balance in everyday life is challenging. Weight loss occurs when EE consistently exceeds energy intake, whereas a sustained positive energy balance promotes weight gain which may lead to obesity. Whole-room indirect calorimetry enables precise 24-h assessment of total EE and its components. Achieving energy balance within a whole-room indirect calorimeter (WRIC) represents a substantial challenge and depends critically on stringent clinical standardization as well as robust technical performance to ensure accurate estimation of energy requirements.

Objective:

To achieve energy balance within a WRIC and to characterize the technical performance of two newly installed WRIC systems.

Methods:

Healthy subjects, aged 18 to 65 years with a body mass index of 18.5 to <40 kg/m² are eligible to participate in the study. Resting EE is measured over 30 minutes and combined with the Mifflin–St. Jeor equation to calculate a personalized weight-maintaining diet (WMTD). Participants consume this WMTD for 3 days in free-living conditions before each 24-hour stay in the WRIC. Before and during WRIC stays, participants are instructed to maintain a low physical activity level (PAL≈1.4; PAL defined as 24-h EE/resting EE). Standardized meals (breakfast 8 AM, lunch 1 PM, dinner 6 PM) are provided inside the WRIC. For the first two WRIC stays, biological validation of the system is performed by repeating EE measurements under identical conditions, that is during these stays, the caloric content of the diet matches the pre-calculated WMTD adjusted for reduced physical activity within the WRIC. For a third WRIC stay, following another 3-day WMTD run-in, the caloric content of the diet is matched to each participant’s average 24-h EE from the two preceding stays and energy balance is calculated. Hereupon, two additional WRIC stays are conducted after another 3-day WMTD run-in and participants are instructed to achieve a higher physical activity level (PAL≈1.7) using cycle ergometry. During the first stay within the WRIC with PAL≈1.7, caloric content of the diet equals the WMTD adjusted for PAL≈1.7. For the following 24-h EE assessment with PAL≈1.7, diet is adjusted such that its caloric content equals the previously measured 24-h EE under increased physical activity and energy balance is reassessed. The day after the last 24-h EE assessments with PAL≈1.4 and PAL≈1.7, respectively, ad libitum energy intake is measured using a buffet to relate individual EE with energy intake. Body weight is monitored throughout the study.

Results:

The trial commenced in August 2025. At the time of manuscript submission, six participants have been enrolled. Based on prior data, a total of 34 participants is required to evaluate the improvement in mean energy balance by 100 kcal with a power >0.80, assuming a standard deviation of 200 kcal. The final analyses will include energy balance, changes in body weight, components of EE, ad libitum energy intake, and circulating hormones involved in appetite regulation and satiety.

Conclusions:

This trial evaluates whether energy balance can be achieved during repeated stays in a WRIC and provides a detailed assessment of the performance of two newly installed WRIC systems.