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  • Karen Buch RDN, LDN

Measuring Metabolism

Metabolism determines how the body uses energy and it can fluctuate. Research published in The New England Journal of Medicine found decreased resting metabolism in 86% of study participants after a caloric reduction to lose 10-20% of body weight, leading to reduced caloric intake for maintaining the new weight. Tracking metabolism may help individuals to more effectively manage caloric balance and adjust dietary intake to match nutritional goals. Indirect calorimetry is the most well-established approach for accurate assessment of resting energy expenditure (REE) and energy expenditure (EE). According to the 2016 position of the Academy of Nutrition and Dietetics—if indirect calorimetry is available, the registered dietitian nutritionist (RDN) should use a measured resting metabolic rate (RMR) to determine energy needs in overweight or obese adults. Traditional indirect calorimetry testing equipment can be bulky, expensive, and complicated to calibrate and operate. Furthermore, using a predictive equation may produce an estimated REE that significantly differs from a person’s true REE value. To address these concerns, a compact, mobile, indirect calorimeter called Breezing® was developed to facilitate personalized REE measurement and tracking. About Breezing® Breezing measures the metabolism using indirect calorimetry. The device uses a sensor cartridge and flow meter to determine the rate of consumed oxygen (VO2) and produced carbon dioxide (VCO2) in the breath. These values are used to determine REE and EE according to the Weir Equation* as well as respiratory quotient (RQ), which is the ratio of produced carbon dioxide to consumed oxygen. The device pairs wirelessly via Bluetooth to the free Breezing mobile app on an iOS or Android smart phone or tablet. The app guides the user to perform the metabolism test, view results, and track history of metabolism, RQ, weight, diet, and activity. Each test requires a single-use sensor cartridge, which conveys its own calibration parameters through a quick response (QR) code scan during the testing process. Starter kit retail price is $349. On-going costs are $1 per mouthpiece and $5 per sensor cartridge. The device was provided to me at no cost for the purpose of review. I spent several weeks interacting with it and reading related literature. My time was compensated. Thoughts and opinions expressed are my own. My Experience with the Device I was particularly interested in learning how to use the device, learning about its accuracy, and determining its usefulness as a tool for dietitians who provide personalized nutritional services to clients that want to improve their level of fitness and weight management. Steps to Use Breezing® to Measure Resting Energy Expenditure (REE) 1. Download the Breezing® app, register, and complete the brief new user training 2. Plan to conduct the testing close to waking time and after fasting overnight (8-hours) ideally, or wait at least 4 hours after eating a moderate-calorie (~500 kCal) meal. 3. Wait at least 4 hours after moderate exercise; wait at least 12 hours after strenuous exercise 4. Be reclined and supported by a cushion in a quiet, comfortable environment 5. Practice breathing through the mouthpiece connected to the T-joint assembly for at least two minutes (while wearing the nose clip; without device attached) and check heart rate to ensure a resting state 6. Attach the Breezing device; press and hold the power button until the breezing logo lights up 7. Scan the QR code on the sensor cartridge package 8. Open/insert a single-use cartridge (“B” is facing up & yellow square at lower right); cover tightly 9. Affix the nose-clip, tap to connect wirelessly, and watch the app for your cue to begin breathing normally through the mouthpiece

When testing is complete, results will post immediately to the app. Allow five minutes between tests while the device completes its self-cleaning and drying process.

Momentary energy expenditure (MEE) measurement is also available for clients wishing to observe metabolic changes due to a various forms of exercise such as aerobic training or weight training.

Is Breezing® accurate? The device was tested in over 300 measurements with human subjects and was found to correlate to the values of the gold-standard Douglas Bag method with no statistical differences found between the two methods.

Is Breezing® an appropriate tool for use in nutrition and fitness counseling? As a dietitian who has experience working to help individuals manage weight and improve their personal level of fitness, I find this tool and its user-friendly mobile interface appealing. In my practice, I measure the client’s weight, metabolism (energy expenditure), and body composition (percentage of body fat) in combination initially, and at key stages during the weight-loss journey to guide individualized nutrition education and fine-tune meal planning. Highly-motivated clients may also be interested in purchasing their own Breezing® device for personal use and routine metabolism tracking over time.

For more info, visit If you decide to make a purchase, enter FN&R discount code to receive 5 free sensor cartridges with your order. References Leibel R, Rosenbaum M, Hirsch J. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995;332:621-628. Raynor HA, Champagne CM. Position of the Academy of Nutrition and Dietetics: Interventions for the treatment of overweight and obesity in adults. J Acad Nutr Diet. 2016;116(1):129-147. Weir JB. New methods for calculating metabolic rate with special reference to protein metabolism. J Physiol. 1949;109(1-2):1-9. Xian X, Quach A, Bridgeman D, Tsow F, Forzani E and Tao N. Personalized indirect calorimeter for energy expenditure (EE) measurement. Glob J Obes Diabetes Metab Syndr. 2015;2(1):004-008.

* Weir equation: REE (kCal/day) = [3.9 (VO2)+1.1 (VCO2)] x 1.44 VO2

A similar version of this product review article first appeared on


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