Calopy

Indirect calorimetry (IC) is the standard non-invasive method for measuring energy metabolism in animals and humans. By tracking oxygen consumption and carbon dioxide production, it quantifies parameters such as energy expenditure, resting metabolic rate and the respiratory exchange ratio — a key indicator of substrate utilization and metabolic flexibility. Modern systems record these signals alongside activity, food and water intake, body temperature and environmental and phenotypic variables at high temporal resolution, producing complex, time-resolved data whose interpretation requires sophisticated statistical methods.

Calopy addresses this need with an open-source, transparent and easy-to-use platform for IC data analysis. Its key capabilities include:

• robust preprocessing, including outlier detection and subject-level removal;
• optional filtering of time-resolved variables to extract noise-robust features (daily maxima and minima, amplitude, area under the curve);
• global and time-resolved estimation of resting and basal metabolic rate from an activity- and food-intake-aware model;
• a comprehensive suite of exploratory tools for statistics on raw and derived features together with all metadata, enabling between-group, temporal-condition and time-window comparisons.

Calopy is built on a modular architecture that cleanly separates data handling, analysis methods and interface, making it readily extensible with new methods. It runs as a free service at www.calopy.app or can be installed locally, is released under the MIT license, and is published in Nature Metabolism (2025).