Respiratory quotient (RQ) and resting metabolic rate (RMR) are approximately the same measure for our purposes. They are estimated by measuring carbon dioxide and oxygen in the breath to determine the rate of carbon dioxide production and rate of oxygen uptake.  The ratio of these two rates (CO2 productions to O2 uptake) provides an indication the amount of metabolism is from carbohydrates as compared to fats.

This measure can answer the question:  What is my ratio of carbohydrate to fat metabolism?

Breath acetone provides an indication of how much fat is being burned – irrespective of carbohydrates.  Breath acetone can indicate an absolute value of fat metabolism (e.g., grams of fat per day).  As you will see below, breath acetone is more sensitive to changes in fat metabolism as compared to RMR and the measurement of breath acetone with LEVL takes seconds vs. minutes.

Examining a data from a published study (Figure 4 from reference 3) shows the relationship between these two measures, RMR/RQ and breath acetone (Figure below).

Breath Acetone vs. RMR

For orientation, the oxidation of different macronutrients are represented by RQ

  • RQ = 1.0 for oxidation of carbohydrate
  • RQ = 0.80 for oxidation of protein
  • RQ = 0.70 for oxidation of fat

As the RQ moves into the fat burning zone (<0.8) RQ doesn’t have as much sensitivity (or accuracy) with respect to changes in breath acetone. As RQ decreases, small RQ changes probably (no data available other than figure below) correspond to large changes in breath acetone. Additionally, RQ is not correlated with the absolute rate of fat metabolism. Breath acetone has been shown to be correlated to fat loss at these low acetone concentrations (1, 2).


  1. Kundu SK, Bruzek JA, Nair R, and Judilla AM. Breath acetone analyzer: diagnostic tool to monitor dietary fat loss. Clin Chem 39: 87-92., 1993.
  2. Anderson, Joseph C. Obesity, vol. 23, no. 12, 2015, pp. 2327–2334., doi:10.1002/oby.21242.
  3. Owen OE, and Reichard GA, Jr. Human forearm metabolism during progressive starvation. J Clin Invest 50: 1536-1545, 1971.
  4. Prabhakar A, Quach A, Wang D, Zhang H, Terrera M, Jackemeyer D, Xian X, Tsow F, Tao N, and Forzanil E. Breath Acetone as Biomarker for Lipid Oxidation and Early Ketone Detection. Global Journal of Obesity, Diabetes and M

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