The Importance of the Respiratory Exchange Ratio in Fat Loss

The Importance of the Respiratory Exchange Ratio in Fat Loss

The Respiratory Exchange Ratio (RER) is one of the most fundamentally important principles for anyone interested in fat loss.

As you know, we inhale oxygen so our bodies can (among other tasks) metabolize glucose, fats, or both to use as fuel. We then exhale carbon dioxide and the process starts anew. RER is calculated by the ratio of oxygen consumed and the carbon dioxide expelled. The method is known as indirect calorimetry.

Simply put, the greater the physical exertion, the higher the RER.
Okay, you're asking. Just how does this help me burn as much fat as possible while retaining the lean muscle tissue ( which you want to preserve because you don't really want to look like an emaciated zombie - regardless of what some fashionista may tell you).
Below, courtesy of NASM, you will see a chart detailing the RER and the percentage of calories derived from carbohydrates, fats, or a combination of the two.

Let's put this into perspective. The body utilizes the highest percentage of it's caloric needs from fats when the RER is at 0.71. The logical conclusion is that we should then exercise at that level to get the most from our efforts.
Unfortunately, a RER of 0.71 is attainable when it is at complete rest when we're sleeping or doing very little on the couch or in bed.
Does this mean we should cancel our gym memberships and find the best deals on down comforters and Lazy Boys? Again, the unfortunate answer is 'no' (you didn't think it was going to be that easy, did you?). Obviously quality sleep is an important part of overall health. However, nothing worth having is possible without a certain amount of effort.

Although you burn 100 percent of calories from fats when the at RER of 0.71, the overall QUANTITY of calories burned is very little. Just how little...? That varies from person to person based on her basal metabolic rate, how active she is, and several other factors. So anyone reading this who is entertaining the notion of having a slice of cheese cake (or two) and going immediately to couch potato mode will be dissapointed.

When walking or jogging, the RER is at about 0.80 to 0.90. This equates to approximately 65-75% of your max heart rate. You should be able to hold a conversation at this pace, although it may become somewhat difficult as you reach the 75% rate.
Please note: I strongly believe jogging is one of the most over rated activities people can do if their main goal is to lose fat; however, I chose it as a reference point since it is something most of us have tried at one time or another.
When engaged in an activity in which you can just barely complete a sentence but need to catch your breath afterwards, the RER is at about 0.91 to 0.95. This equates to approximately 80-85% of your max heart rate.

When engaged in an activity in which you are exerting so much effort that you can't utter one single word (imagine being chased by an angry dog), the RER is at 1.0 or slightly less. This, obviously, is at 100% of your max heart rate.
For those who've stayed awake to this point (I commend you), you may be thinking to yourself: "This ain't so bad. I'll just work at a RER of about 0.80. It's a fairly challenging pace and I won't have to suffer."
That's not a bad game plan. However, in order to sculpt the best physique your genetics will allow, chances are pretty good that you'll have to exercise at a slightly higher level.

And even if you don't plan to grace the cover of a magazine or win a physique contest, the body does need to be challenged - gradually and intelligently, of course.

Yes, this means an intelligent strength program.

A universal truth in physiology is that lean muscle tissue is metabolically expensive; this is a fancy way of saying that you if you increase the amount of lean tissue your metabolism will be higher (which equates to more calories burned).

And please don't worry - most women simply cannot look like some of those steroid-injected men you see all oiled up and flexing in a banana hammock. As I stated in another article, the chances of a woman looking like that as the result of an intelligent strength and conditioning program is less than getting struck by lightening while relaxing inside your favorite coffee house.

Also factor in that, the day after a challenging strength workout, your body's metabolic demands are higher because of the repair process it must go through. Indeed, within hours of a challenging workout, the body burns more calories IF the RER was sufficiently high enough during the workout. The process is called Excess Post Exercise Oxygen Consumption (EPOC).

Does this mean I expect all of your workouts to make you feel as if the grim reaper is hovering above you? Absolutely not. Any idiot trainer can make her client sweaty and tired at the end. It's the rarest of trainers that can design and implement a program that is challenging, safe both short and long term, and enjoyable (well, as enjoyable as exercise can be).

This is a simplified version. I can bog things down by going into further detail about the various energy systems involved but, for better or worse, most people are not interested (of course, I'll be happy to discuss the matter in greater detail in person with anyone who is). The bottom line is, the information presented should be sufficient to nudge a paradigm shift in how you view exercise and caloric expenditure.

So how does one juggle the strength training with the challenging cardio with the the moderate to easy sessions...? There is no one-size fits all approach. Those who ignore this and purchase the latest Wii or dvd are setting themselves up for frustration and possibly injury.

This is where I come in. Meet me for a free introductory session and see for yourself how I can custom design a program that will give you results and keep you safe in the process. Furthermore, let's talk about how I can teach you to be self reliant so that you have the knowledge to be your own Personal Trainer. (what's that saying about teaching someone to fish...?)
And for those who aren't convinced, well I'm sure there's sale somewhere on a Lazy Boy.

What is respiratory exchange ratio (RER)? What is respiratory quotient (RQ)?

What is respiratory exchange ratio (RER)? What is respiratory quotient (RQ)?

Useful Resources - Lung Function Testing

Prepared by Dr Ma Hon Ming, SMO TPH (M&EC) and Dr Lo Ho Yin, MO AHNH (Med)
RER is the ratio of carbon dioxide output to oxygen uptake (VCO2 / VO2) measured at the mouth ie external respiration whereas RQ is the ratio of CO2 production to O2 consumption through tissue metabolism (mCO2 / mO2) ie cellular respiration. RER approximates RQ only at steady state conditions when VO2 = m02 and VC02= mCO2 (eg at rest or after 3-4 min steady state exercise at constant workload). In clinical practice, RER is more readily obtained by measuring VCO2 and VO2. In steady states, RQ = RER. In non-steady states, dynamic RER values reflects active coupling of external respiration to cellular respiration.

In metabolic assessments by indirect calorimetry (either open circuit using canopy or close circuit for patients on ventilator), VCO2, VO2 and RER are obtained. RQ = RER in steady state. Based on known values of RQ (carbohydrate 1.0, protein 0.82, fat 0.71, mixed diet 0.85, ketosis 0.67 to 0.7, lipogenesis 1.0-1.2) and urinary nitrogen excretion of patients, we can assess their caloric and metabolic status. The goals are to ensure adequate caloric intake, to optimise nutritional formula and avoid overfeeding to prevent excessive CO2 production that escalates ventilatory demands. Dietary manipulation may change RQ. Physical fitness & endurance training can also change RQ through increased energy utilisation from fatty acid metabolism at a given workload.

In cardiopulmonary exercise testing, RER is derived from breath by breath O2 and CO2 flow measurements at the mouth. RER at rest stays ~ 0.8 (Westernised food). However, subjects who are anxious or hyperventilating for various reasons often have RER> I. Thus, VE and EtCO2 should be taken into consideration when interpreting RER values. During exercise, changes in cellular respiration needed to increase energy output are closely linked to external respiration through the circulation.

Studies on VCO2- VO2 relationship (V-slope) gave us valuable insights into our body wisdom. During exercise with cycle ergometer at increasing work rates (ramp), a steady state for VCO2 & VO2 is achieved at 3 to 4 min at work rates not causing increase in arterial lactate. This is the lower 'aerobic' component slope SI (RER ~ 0.95 corresponding to increase carbohydrate utilization during exercise). With glycogen depletion study (fasting and vigorous exercise on preceding day), SI falls to 0.79-0.81, showing that SI in V-slope plot below anaerobic threshold (AT) represented muscle substrate RQ.

With progressive increase in work rates, capillary PO2 reaches a 'critical' level below which mitochondria cannot consume oxygen (N~ l4mmHg, chronic stable heart failure~ 22mmHg) and lactate rises significantly. VO2 continues to increase at a rate proportional to the rise in lactate but VCO2 further diverges from VO2 increase due to extra CO2 release from cells as HCO3- buffered lactic acid. This is the steeper, upper 'anaerobic' component slope S2. This CO2 rise and HCO3- consumption shifts the O2 dissociation to the right (Bohr effect). Thus lactic acidosis serves to facilitate O2 dissociation and O2 transport to muscle cells without further reduction in end-capillary PO2. From this stage onward, RER is > 1.

AT occurs around a normal subject's mid-work capacity, not at V02 max. RER continues to increase as exercise progresses, up to > 1.6 in short duration, high work rate testing. During cool down, RER returns rapidly to baseline levels with occasional shoot-ups from hyperventilation. RER at peak exercise> 1 (eg RER >1.15 in some computerised ramp protocol) is often taken as indicator that a subject has made good effort. This contrasts with those with 'functional' impairment whose RER always stays < 1 with very high breathing and heart rate reserve even at 'peak' exercise.

(Food for thoughts or exams! - 1) RQ differences: male vs female, obese vs lean, hyperthyroid vs euthyroid, changes with age and pregnancy. 2) RER changes during exercise in COPD. Answers can befound in the references below)


References
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