What does a respiratory quotient (RQ) of 1.2 indicate?

Respiratory Quotient (RQ) of 1.2 Indicates Lipogenesis

A respiratory quotient (RQ) of 1.2 indicates lipogenesis, which occurs when excess carbohydrates are converted to fat in the body. 1

Understanding Respiratory Quotient

The respiratory quotient (RQ) is defined as the ratio of carbon dioxide production (VCO₂) to oxygen consumption (VO₂) and reflects the metabolic substrate being utilized by the body:

• RQ of 1.0 indicates metabolism primarily of carbohydrates 1
• RQ of approximately 0.7 indicates metabolism primarily of fat 1
• RQ of approximately 0.8 indicates metabolism primarily of protein 1
• RQ greater than 1.0 indicates lipogenesis (conversion of excess carbohydrates to fat) 2, 3

Physiological Basis of RQ > 1.0

When RQ exceeds 1.0, it typically indicates one of the following conditions:

• Lipogenesis: The primary cause of an RQ of 1.2 is net fat synthesis from excess carbohydrates, which requires additional CO₂ production relative to O₂ consumption 2
• Hyperventilation: Can artificially elevate RQ due to excess CO₂ being exhaled from body stores 1
• Lactic acid accumulation: Can increase CO₂ production as bicarbonate buffers lactic acid 1

Clinical Significance of RQ = 1.2

An RQ of 1.2 has important clinical implications:

• Indicates overfeeding: Particularly with carbohydrate-rich nutrition support regimens 2, 3
• Associated with respiratory compromise: Elevated RQ correlates with increased respiratory rate and decreased tidal volume, potentially causing ventilatory issues in patients with limited pulmonary reserve 3
• Metabolic inflexibility: High and fixed RQ values may indicate reduced metabolic flexibility, which is associated with obesity 4

Differentiating RQ from RER

It's important to note the distinction between:

• Respiratory Quotient (RQ): Reflects metabolic exchange of gases at the tissue level 1
• Respiratory Exchange Ratio (RER): Measured at the mouth and reflects not only tissue metabolism but also transient changes in body gas stores 1

Under steady-state conditions, RER equals RQ, but during non-steady states (like hyperventilation), they may differ 1

Clinical Applications

• In nutrition support, an RQ > 1.0 has a specificity of 85.1% for identifying overfeeding, though sensitivity is lower at 38.5% 3
• Monitoring RQ can help adjust nutrition support regimens to prevent overfeeding and associated respiratory complications 2, 3
• RQ variance (ability to change RQ in response to different activities) is inversely associated with obesity, suggesting better metabolic health with greater flexibility 4

Common Pitfalls

• Interpreting elevated RQ without considering non-metabolic factors like hyperventilation or acid-base disturbances 1
• Using RQ alone to make fine adjustments to nutrition support regimens (not recommended due to limited sensitivity) 3
• Failing to distinguish between RQ (tissue level) and RER (measured at mouth) when interpreting results 1