Respiratory Exchange Ratio & Fat Burn

(Michael - Don't expect miracles and you won't be disappointed.) #1


The respiratory exchange ratio (RER) is the ratio between the amount of carbon dioxide (CO2) produced in metabolism and oxygen (O2) used to produce it. The ratio is determined by comparing exhaled gases to room air. Measuring this ratio can be used for estimating the respiratory quotient (RQ). RQ can be used as an indicator of which fuel, carbohydrate or fat, is being metabolized to supply the body with energy and the proportions of each being burned.

RER is about 0.8 at rest with a standard American diet (SAD). This value, however, can exceed 1.0 during intense exercise, as CO2 production by the working muscles becomes greater and more of the inhaled O2 gets used rather than being expelled. During moderate or higher intensity exercise, both aerobic and anaerobic, the accuracy of RER for estimating RQ declines due to several factors affecting CO2 levels being expelled by the respiratory system.

An RER of 0.70 indicates that fat is the predominant fuel source, RER of 0.85 suggests a mix of fat and carbohydrates, and a value of 1.00 or above is indicative of carbohydrate being the predominant fuel source.

The Equations

Oxidation of a carbohydrate molecule:

6 O2 + C6H12O6 → 6 CO2 + 6 H2O + 38 ATP
RER = VCO2/VO2 = 6 CO2/6 O2 = 1.0

Oxidation of a fatty acid molecule:

23 O2 + C16H32O2 → 16 CO2 + 16 H2O + 129 ATP
RER = VCO2/VO2 = 16 CO2/23 O2/ = 0.7


Table of RER, carb and fat ratios:



Home usable devices to measure RER are becoming available and we may soon have reliable methods to measure fat burn directly and accurately. I started a topic on one such device here. As I encounter others either currently available or in development I will note them in this topic.

What do you think, are the days of obsessing over ketone numbers soon to be eclipsed by simple and direct measure of actual fat burn via the ratio: VCO2/VO2?

Cant get back into ketosis
Testing enhanced fat burn with raw whole ginger root
(Michael - Don't expect miracles and you won't be disappointed.) #2

I’ve discovered another portable, personal device called the Breezing that is actually shipping and can be purchased on Amazon. The emphasis is definitely CICO, but it also indicates carb/carb&fat/fat burn. I don’t know if it displays a carb/fat ratio or not.


Alert: Breezing has consumables! One-use sensor cartridges at $5 a pop. That would be a show stopper for me, since I would like to test multiple times per day, like I do with my Ketonix.

(Bob ) #3

Fascinating, Michael. Thanks for the info!

Like you, I’d be very reluctant to get something with a $5 per use cost. I’ll take your word on the Lumen not having that. I watched the video but didn’t explore their site much.

Definitely one to keep an eye out for.

(Michael - Don't expect miracles and you won't be disappointed.) #4

@CFLBob One of Lumen’s advertising points is one-time cost of purchase. At US$299 purchase price is less than Breezing.

The Breezing is currently not available on Amazon, so no listed price for the device itself. Breezing’s store only lists package prices that includes a Samsung tablet. The cheapest for US$470. There’s another ‘Professional’ version for $200 more! There are so many different Samsung tablets at various prices it’s impossible to determine the price of the Breezing itself.

(Bunny) #5

I wonder that too, I’m thinking this method could give you a personal breakdown on how much NOT to eat?

e.g. half an egg, half slice of bacon and a sliver of avocado to meet your daily fat burning requirement ratio!

(Karim Wassef) #6

Unless there’s some data that correlated the cheap home test to the lab grade test, I don’t know how usable it really is.

It would be great if it worked. I almost considered shelling out $3000 for an RMR tester since that’s the one variable I really wish I could capture consistently and frequently.