Oxygen is inhaled. Carbon Dioxide is exhaled. Water is lost in breath, wee, poo, sweat & other bodily fluids.
As 6 molecules of Oxygen produce 6 molecules of Carbon Dioxide, the Respiratory Exchange Ratio (RER) is 6/6 = 1
Converting molecular weights into their gram equivalents, 180g of Glucose combines with 192g of Oxygen to produce 264g of Carbon Dioxide plus 108g of water plus ~3,012kJ of energy. I'm using kJ rather than kcal, as the human body expends energy as mechanical energy (force x distance) and heat energy.
2. Oxidation of Fat in the body.
Fat is three fatty acids (Stearic Acid, say) attached to a Glycerol backbone. As ~95% of the energy released from a fat is from the three fatty acids, I'm ignoring the Glycerol backbone, to keep the maths as easy as possible. Stearic Acid is CH3(CH2)16COOH. I'm approximating it to 18(CH2), to keep the maths as easy as possible.
54(CH2) + 81(O2) → 54(CO2) + 54(H2O) + energy
Oxygen is inhaled. Carbon Dioxide is exhaled. Water is lost in breath, wee, poo, sweat & other bodily fluids.
As 81 molecules of Oxygen produce 54 molecules of Carbon Dioxide, the RER is 54/81 = 0.67
Note: The RER for fats is actually 0.7, as the Glycerol backbone is converted into Glucose by the liver. As the RER for Glucose is 1, this raises the RER of my approximated fat by ~5%.
Converting molecular weights into their gram equivalents, 756g of approximated fat combines with 2,592g of Oxygen to produce 2,376g of Carbon Dioxide plus 972g of water plus ~28,468kJ of energy.
This doesn't invalidate Energy Balance, as the kcal/kJ values for foods merely represents the amount of chemical energy that can be released by oxidation of the various fuels in the foods. See Why Calories count (where weight change is concerned).
"The human body does not need carbohydrates from an external food source, because it is capable of very precisely and correctly assembling its own amounts of glucose that is needed in very small amounts for auxiliary and specialized functions." - Igor Butorski.
After liver glycogen has been depleted in starvation or on Nutritional Ketosis (Ketogenic Diets with less than 14% of total energy from Protein), total glucose production from liver & kidneys is ~100g/day.
From It's all in a day's work (as measured in Joules), the body oxidises carbohydrate at a rate exceeding ~4g/hour at exercise intensities exceeding ~25%, on a LCHF diet. This is unsustainable.
EDIT: If protein is consumed, total glucose production increases, up to a maximum of ~400g/day.
3)It's wasteful. Glucose production from protein converts ~50% of the most expensive macronutrient (protein) into the cheapest macronutrient (carbohydrate). It creates expensive urine, as the nitrogen part of amino acids is detoxified by being converted into urea by the liver and then wee'ed out by the kidneys.
4) Using the above argument, the human body does not need saturated fats & monounsaturated fats from an external food source, because it is capable of very precisely and correctly assembling its own amounts of saturated fats & monounsaturated fats (out of carbohydrate) that are needed in very small amounts for auxiliary and specialized functions.
If we consume only Essential Fatty Acids, Essential Amino Acids, Vitamins, Minerals, Fibre/Fiber, Water & Anutrients, there won't be much to eat. Also, there won't be a source of chemical energy to generate heat energy & mechanical energy. That's what dietary carbohydrates & fats are for!
Respiratory Exchange Ratio/Respiratory Quotient (RER/RQ) varies with carbohydrate & fat intake, as the body preferentially oxidises the fuel that's most readily available, when it's working properly. If it's not working properly, due to Insulin Resistance (IR), fix the IR rather than kludge the diet (by eating LCHF) to compensate for it. See Insulin Resistance: Solutions to problems for how to do this.
RER/RQ varies with Exercise Intensity. Low-intensity exercise results in mostly fats being oxidised. High-intensity exercise results in mostly carbohydrates being oxidised. Medium-intensity exercise results in a mixture of fats & carbohydrates being oxidised.
Having explained how low & very low-carbohydrate diets work, here are a few ways in which they don't work.
Uh, nope!
1. Hormonal clogs: This is a term used by Jonathan Bailor. I don't think he's referring to wooden shoes! The "clog", I'm guessing, is supposedly caused by that dastardly hormone insulin. Uh, nope!
See the following plots of RER vs exercise intensity after being on high-fat diet or low-fat diet.
RER = 0.7 ≡ 100%E from fat. RER ≥ 1.0 ≡ 100%E from carb.
The low-fat diet results in higher RER, so the body is burning a higher %E from carb and a lower %E from fat.
However, this doesn't make any difference to weight loss, as it's merely a substrate utilisation issue. In addition, when the body is burning a higher %E from carb, this depletes muscle glycogen stores faster, which lowers RER during the course of the exercise. So, it's not a problem.
2.Insulin: This is Gary Taubes' hypothesis. Insulin makes your body storecarbohydrates as body fat. Uh, nope!
The only time that there's significant hepatic DNL is when there's chronic carbohydrate over-feeding. If you eat sensibly, there's no significant hepatic DNL.
From Second Law of Thermodynamics:-
"Living organisms are often mistakenly believed to defy the Second Law because they are able to increase their level of organization. To correct this misinterpretation, one must refer simply to the definition of systems and boundaries. A living organism is an open system, able to exchange both matter and energy with its environment."
People on ketogenic diets excrete very few kcals as ketone bodies. See STUDIES IN KETONE BODY EXCRETION (PDF). There is no significant Metabolic Advantage with low-carbohydrate diets.
Salient points:
1) Excessively high serum FFA a.k.a. NEFA is bad.
2) Respiratory Quotient (RQ) a.k.a. Respiratory Exchange Ratio (RER) changes due to dietary changes are more sluggish in the MI than in the MF.
3) Under Insulin Clamp conditions, RQ/RER is lower in the MI than in the MF, due to impairment of glucose oxidation and non-oxidative glucose disposal.
In the first article, Danny Roddy writes:-
"Additionally, taking magnesium while actively engaging in a diet or
lifestyle that reduces the respiratory quotient (e.g., high-fat diet,
light deficiency, excessive exercise) seems pretty silly. For example,
as a rule, diabetics have a reduced respiratory quotient (Simonson DC,
et al. 1988), tend to have higher levels of free fatty acids or NEFA
(Kahn SE, 2006), and are often deficient in magnesium (De Valk HW,
1999)."
The second sentence (diabetics have a reduced respiratory quotient...and are often deficient in magnesium) seems to contradict the first sentence (...taking magnesium while actively engaging in a diet or
lifestyle that reduces the respiratory quotient seems pretty silly).
Simonson DC,
et al. 1988 is Oxidative and non-oxidative glucose metabolism in non-obese type 2 (non-insulin-dependent) diabetic patients.
"In conclusion, during the postabsorptive state and under conditions of
euglycaemic hyperinsulinaemia, impairment of glucose oxidation and
non-oxidative glucose disposal both contribute to the insulin resistance
observed in normal weight Type 2 diabetic patients. Since lipid
oxidation was normal in this group of diabetic patients, excessive
non-esterified fatty acid oxidation cannot explain the defects in
glucose disposal."
Impaired glucose oxidation with normal lipid oxidation lowers RQ/RER. Therefore, lower RQ/RER must be bad, right? Wrong. From the above study:-
"...euglycaemic insulin clamp studies were performed..."
Remember Salient point 3)? Simonson DC,
et al. 1988 is an insulin clamp study, the results of which don't apply to free-living people (who aren't insulin clamped).
RER has been mentioned a few times on this blog. By measuring the rate of CO2 exhaled and the rate of O2 inhaled, it's possible to work out how many kcals/min the body is generating from food at any instant and from what fuel mixture.
An RER of 0.700 means that 100% of energy is being generated from fat.
An RER of 1.000 means that 100% of energy is being generated from carbohydrate aerobically.
An RER of >1.000 means that 100% of energy is being generated from carbohydrate, some aerobically and some anaerobically.
How does this work? Fats are an ester of fatty acids + glycerol. Acid + Alcohol = Ester + Water.
Saturated fatty acids (the easiest type to calculate) have the generic formula CH3(CH2)nCOOH, where n can be from 0 to 16. Here are some saturated fatty acids and their n values:- Acetic (0), Propionic (1), Butyric (2), Lauric (10), Myristic (12), Palmitic (14) and Stearic (16). The total number of carbon atoms in each fatty acid is n+2. Stearic acid is mostly CH2s, so I'll approximate fat to n(CH2).
n(CH2) + 3/2n(O2) = n(CO2) + n(H2O) + Heat. The ratio of CO2 to O2 is 2/3, so RER = 0.666.
As fats contain things other than CH2 (e.g. glycerol CH2OHCHOHCH2OH), this raises RER to 0.700. Burning protein gives an RER = 0.800.
Carbohydrates have the generic formula n(CH2O), where n = 6 for glucose.
n(CH2O) + n(O2) = n(CO2) + n(H2O) + Heat. The ratio of CO2 to O2 is 1.000, so RER = 1.000.
So how on earth can Eskimos have an RER = 0.600? I have a theory. When hydrogen is oxidised, water only is produced. There is no CO2, so RER = 0.000. Therefore, if some hydrogen was being burned (by gut bacteria, say), this could result in RER falling below 0.700. Maybe...
I'm not quite sure what the picture below means (I need to do a spot of reading!).
Metabolic flexibility "bowl" and "Adaptability envelope"
While replying to Kade Storm this morning, it suddenly occurred to me that the Eskimos have an unusual ability. RER (a.k.a. RQ) normally varies from 0.7 (100% fat-burning) to 1.0 (100% carb-burning aerobically) to >1.0 (100% carb-burning, some anaerobically). Eskimos manage to get an RER of 0.600 *Mind blown.*
One theory that comes to mind is BAT. As Eskimos live in a very cold environment, it's possible that this has resulted in them having a large amount of BAT. BAT is very metabolically-active and turns ATP into heat via UCPs.
Nowadays, first-world people don't live in a cold environment (unless they're old and/or poor), so we don't have much BAT after infancy. Naturally-skinny people may be that way due to having more BAT. They seem to be able to eat whatever and as much as they want without getting fat. I'd like to scratch their eyes out! ;-)
The title of this blog post is from the "Physics Man" sketch on The Now Show. Work (also heat) is another word for energy and there are two different units for it.
The calorie (cal) is the amount of energy required to heat 1g of water by 1°C. This is a tiny amount of energy. The dietary Calorie (Cal) = 1,000cal = 1kcal.
The Joule (J) is the SI unit of energy. 1J = 1kg*m^2/s^2.
1Joule/sec = 1Watt (W).
1kcal = 4.186kJ.
At rest, an average human body uses ~1kcal/min = ~4,186J/min = ~69.8J/sec = ~69.8W.
The brain uses ~5g of glucose/hour = 18.75kcal/hour (1g of carb = 3.75kcals, usually rounded-up to 4) = 78487.5J/hour = ~21.8W.
The heart uses ~10W. The liver, kidneys, gut and lungs run continuously so they use energy all of the time.
Skeletal muscle uses a variable amount of energy using a variable proportion of fuels, depending on what you're doing with it. A chap called Steve sent me a spreadsheet of results in 2004 when he underwent a metabolic test on a stationary bike while breathing through a respiratory gas analyser, which calculated kcals oxidised and fuel utilisation by measuring Respiratory Exchange Ratio (RER).
At 1kcal/min (resting), he oxidised ~95% from fat (~0.11g/min), ~5% from carb (~0.01g/min).
At 2kcal/min (12% max), he oxidised 100% from fat (0.22g/min), 0% from carb (0.00g/min).
At 3kcal/min (18% max), he oxidised 100% from fat (0.33g/min), 0% from carb (0.00g/min).
At 4kcal/min (24% max), he oxidised 99% from fat (0.44g/min), 1% from carb (0.01g/min).
At 5kcal/min (29% max), he oxidised 48% from fat (0.27g/min), 52% from carb (0.69g/min).
At 6kcal/min (35% max), he oxidised 62% from fat (0.41g/min), 38% from carb (0.61g/min).
At 7kcal/min (41% max), he oxidised 58% from fat (0.45g/min), 42% from carb (0.78g/min).
At 8kcal/min (47% max), he oxidised 46% from fat (0.41g/min), 54% from carb (1.15g/min).
At 9kcal/min (53% max), he oxidised 42% from fat (0.53g/min), 58% from carb (1.39g/min).
At 10kcal/min (59% max), he oxidised 44% from fat (0.49g/min), 56% from carb (1.49g/min).
At 11kcal/min (65% max), he oxidised 38% from fat (0.46g/min), 62% from carb (1.82g/min).
At 12kcal/min (71% max), he oxidised 41% from fat (0.55g/min), 59% from carb (1.89g/min).
At 13kcal/min (76% max), he oxidised 37% from fat (0.53g/min), 63% from carb (2.18g/min).
At 14kcal/min (82% max), he oxidised 30% from fat (0.47g/min), 70% from carb (2.61g/min).
At 15kcal/min (88% max), he oxidised 14% from fat (0.23g/min), 86% from carb (3.44g/min).
At 16kcal/min (94% max), he oxidised 0% from fat (0.00g/min), 100% from carb (4.27g/min).
At 17kcal/min (100% max), he oxidised 0% from fat (0.00g/min), 100% from carb (4.53g/min).
There are some interesting points about Steve's data:
1. Over a wide range of exercise intensities, the number of grams of fat Steve oxidised/min was fairly constant.
2. Up to 24% of maximum exercise intensity, Steve derived almost 100% of his energy from the oxidation of fat. Steve was on a LC diet, which shifts fuel usage away from carb and towards fat. This is known as "fat-adaptation".
3.Despite fat-adaptation, above about 45% of maximum exercise intensity, Steve derived more energy from the oxidation of carb than the oxidation of fat.
4.Despite fat-adaptation, above about 80% of maximum exercise intensity, Steve derived almost all of his energy from the oxidation of carb rather than the oxidation of fat.
Note that 17kcals/min = 1186.6W, or 1.19kW! Steve was aerobically fit. A less aerobically fit person derives a higher % of energy from the oxidation of carb than an aerobically fit person. This level of exercise intensity can be maintained for a few seconds only, as carb is oxidised both aerobically and anaerobically, which exhausts PhosphoCreatine stores in muscles and also causes an accumulation of lactate in muscles.
