Respiratory Exchange Ratio

The Respiratory Exchange Ratio (RER) is a measure of how much carbon dioxide (CO₂) you produce compared to how much oxygen (O₂) you consume during respiration. It helps assess which type of fuel your body is using for energy—carbohydrates or fats. An RER close to 0.7 indicates fat is the primary source, while an RER near 1.0 suggests carbohydrates are the main fuel. During intense exercise, RER can exceed 1.0 due to increased CO₂ production from acid buffering. RER provides insights into metabolic processes and energy expenditure during activity.