A *very* special dual-fuel car analogy for the human body that I just invented.

The human body is like a very special dual-fuel car.

From http://www.aa1car.com/library/alternative_fuels.htm

In this very special dual-fuel car:-

Glucose is represented by Ethanol, 'cos Ethanol is a carbohydrate, according to Robert Lustig ;-)
Glucose is C₆H₁₂O₆. Ethanol is C₂H₆O. 3(C₂H₆O) = C₆H₁₈O₃. It's not very close, but it'll do!

Caprylic acid is represented by Octane, 'cos fatty acids are hydrocarbons, don'tcha know? ;-)
Caprylic acid is CH₃(CH₂)₆COOH and Octane is CH₃(CH₂)₆CH₃, which is actually pretty close.

Storage depots:

 

Carbohydrates:

For Ethanol, there's a large storage tank (≡ muscle glycogen) and a small storage tank (≡ liver glycogen).
The contents of the large storage tank cannot be used to top-up the small storage tank, but the contents of the small storage tank can be used to top-up the large storage tank. The contents of the small storage tank are used to fuel a generator (≡ HGP) to keep the ECU (≡ brain) working at all times. The contents of the large storage tank are used to fuel the engine.

Fats:

For Octane, there's a large storage tank (≡ subcutaneous fat deposits) and a small storage tank (≡ visceral fat deposits). The contents of the small storage tank are used to produce hormones etc. The contents of the large storage tank are used to fuel the engine.

Substrate Utilisation:

When the car is driven at low speed, the engine burns mostly Octane (≡ RQ=0.7).
When the car is rapidly accelerating or driven at high speed, the engine burns mostly Ethanol (≡ RQ=1).
When the car is being driven intermediately, the engine burns a mixture of Octane & Ethanol.

Overeating/Undereating:

 

Carbohydrates:

If the large Ethanol storage tank becomes full, excess Ethanol goes to the small storage tank.
If the small storage tank becomes full, a gizmo kicks-in and converts excess Ethanol into Octane (≡ DNL).
It also shifts fuel usage of the engine towards Ethanol, to deplete Ethanol as quickly as possible.
Octane accumulating in the small storage tank causes it to malfunction (≡ fatty liver).

Conversely, if the small storage tank becomes nearly empty, it shifts fuel usage of the engine towards Octane, to conserve Ethanol.

Fats:

If the large Octane storage tank becomes full, excess Octane goes to the small storage tank.
If the small storage tank becomes full, it produces too much hormones and the car malfunctions.

How low-carbohydrate diets are (incorrectly) explained to work.

Having explained how 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 fairies: During the night, the insulin fairy comes and makes your body store your bed-time carbohydrates as body fat. Uh, nope!

The only time that there's significant hepatic DNL is when there's chronic carbohydrate over-feeding. If you've been overeating carbohydrates all day, bed-time carbohydrates add to the chronic surplus and there is significant hepatic DNL. Who knew?

If, on the other hand, you've been eating sensibly all day, there will be no significant hepatic DNL of bed-time carbohydrates. In fact, bed-time carbohydrates produce a calm feeling (due to increased serotonin) and a drowsy feeling (due to melatonin) making it easier to sleep. Enjoy your night-cap!

3) A Calorie isn't a Calorie, where weight change is concerned: "A calorie is a calorie" violates the second law of thermodynamics, therefore there's a metabolic advantage with low-carbohydrate diets. Uh, nope!

Where to start? Evelyn Kocur knows her Physics, so I'll start there. See The first law of thermodynamics (Part 1) and The first law of thermodynamics (Part 2).

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. There is no significant Metabolic Advantage with low-carbohydrate diets.

Everyone is Different, Part 2.

Cont'd from We are not all the same.

A long, long time ago...


I learned that Everyone is Different, thanks to a study by Julia H. Goedecke, Alan St Clair Gibson, Liesl Grobler, Malcolm Collins, Timothy D. Noakes and Estelle V. Lambert.

Well, stone the flamin' crows! Timothy D. Noakes' name just popped up in Alan Aragon's article 2013 NSCA Personal Trainers Conference: Looking Back at my Debate with Dr. Jeff Volek. Dr. Noakes has had problems with his blood glucose level and has adopted a very-low-carb/ketogenic diet.

What also caught my eye in Alan Aragon's article was (Note: TTE = Time To Exhaustion):-
"However, the authors’ conclusion is misleading since 2 of the 5 subjects experienced substantial drops in endurance capacity (48 and 51-minute declines in TTE, to be exact). One of the subjects had a freakishly high 84-minute increase in TTE, while the other increases were 3 and 30 minutes."

I expect that the subjects with 84 and 30 minute increases in TTE would be praising ketogenic diets, whereas the subjects with 48 and 51 minute declines in TTE would be cursing them and the subject with 3 minutes increase would be "Meh". Vive la difference!

Also note that sprint capability...remained constrained during the period of carbohydrate restriction. As mentioned in It's all in a day's work (as measured in Joules), exercise above a certain intensity (~85%VO2max) burns significant amounts of carbs, no matter how fat-adapted someone is.

Cont'd on Everyone is Different, Part 3.

It's all in a day's work (as measured in Joules) Part 2.

Are you as aerobically-fit as this bloke?

Emmanuel Mutai made it a Kenyan double after winning the Virgin London Marathon in a new course record. Mutai's time of 2:04.38, beats the previous best of 2:05.10 set by Samuel Wanjiru in 2009 and also the fifth-fastest time ever.

I'll take it that's a "no", then.

Elite marathon runners have optimised their metabolisms to use the minimum possible amount of muscle glycogen as fuel. Muscle glycogen storage is limited to ~1,680kcals-worth (~420g of carb)*.
Supercompensation (depletion followed by 3 days of carb-loading) can increase this figure to ~720g*.
Fat storage can amount to ~35,000kcals-worth (~10lb of fat), even in a skinny Kenyan like Mutai.

A blogger called Thor Falk took the data from It's all in a day's work (as measured in Joules) and plotted it as a graph in Fat vs carb burning – a N=1 chart. Here's the graph:-

Even a super-fit Kenyan like Mutai burns some carbs when running at ~12.5 miles per hour. The less fit that somebody is, the more the first corner in the blue plot moves down and to the left. This results in more carbs being burned at energy consumption levels more than the first corner. This depletes muscle glycogen stores faster, resulting in "hitting the wall" (running out of muscle glycogen) sooner.

Muscles that are depleted of glycogen are more insulin-sensitive than muscles that have more glycogen, therefore the less aerobically-fit somebody is, the sooner their muscles become insulin-sensitive when they exercise.

*Assuming 20kg of muscle (Lore of Running P104)

It's all in a day's work (as measured in Joules)

The title is from the "Physics Man" sketch on The Now Show. Work 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 burned and fuel usage by measuring Respiratory Exchange Ratio (RER).

At~1kcal/min (resting), he burned ~95% from fat (~0.11g/min), ~5% from carbs (~0.01g/min).
At 2kcal/min (12% max), he burned 100% from fat (0.22g/min), 0% from carbs (0.00g/min).
At 3kcal/min (18% max), he burned 100% from fat (0.33g/min), 0% from carbs (0.00g/min).
At 4kcal/min (24% max), he burned 99% from fat (0.44g/min), 1% from carbs (0.01g/min).
At 5kcal/min (29% max), he burned 48% from fat (0.27g/min), 52% from carbs (0.69g/min).
At 6kcal/min (35% max), he burned 62% from fat (0.41g/min), 38% from carbs (0.61g/min).
At 7kcal/min (41% max), he burned 58% from fat (0.45g/min), 42% from carbs (0.78g/min).
At 8kcal/min (47% max), he burned 46% from fat (0.41g/min), 54% from carbs (1.15g/min).
At 9kcal/min (53% max), he burned 42% from fat (0.53g/min), 58% from carbs (1.39g/min).
At 10kcal/min (59% max), he burned 44% from fat (0.49g/min), 56% from carbs (1.49g/min).
At 11kcal/min (65% max), he burned 38% from fat (0.46g/min), 62% from carbs (1.82g/min).
At 12kcal/min (71% max), he burned 41% from fat (0.55g/min), 59% from carbs (1.89g/min).
At 13kcal/min (76% max), he burned 37% from fat (0.53g/min), 63% from carbs (2.18g/min).
At 14kcal/min (82% max), he burned 30% from fat (0.47g/min), 70% from carbs (2.61g/min).
At 15kcal/min (88% max), he burned 14% from fat (0.23g/min), 86% from carbs (3.44g/min).
At 16kcal/min (94% max), he burned 0% from fat (0.00g/min), 100% from carbs (4.27g/min).
At 17kcal/min (100% max), he burned 0% from fat (0.00g/min), 100% from carbs (4.53g/min).

Over a wide range of intensities, the number of grams of fat Steve burned/min was fairly constant.

Note that 17kcals/min = 1186.6W, or 1.19kW. This level can be maintained for only a few seconds, as carbs are burned both aerobically and anaerobically, which exhausts PhosphoCreatine stores in muscles and also causes an accumulation of lactate in muscles. See Why do muscles hurt after exercise?

Muscle mass is very metabolically-active compared to fat mass, as one pound of fat mass burns only about 2kcal a day. See also Dissecting the Energy Needs of the Body – Research Review

Here's another Physics Man.

Everyone is Different.

If there's one thing I've learned over the years of research into Diet and Nutrition, it's this: Everyone is Different. When I first discovered low-carbohydrate diets (thanks to the late Dr Robert C. Atkins M.D.), I thought that it was the One True Diet, and I became a bit of an "Atkins bore" telling everyone how wonderful it was and suggesting that everyone should be on it. I now know that what suits me doesn't necessarily suit everyone else.

To illustrate how variable people are, here's Fig. 2 from Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. Used with permission.

Respiratory Exchange Ratio (RER) (a.k.a. Respiratory Quotient (RQ)) is the ratio of carbon dioxide breathed out to oxygen breathed in. This ratio depends on the fuels that the body is burning for energy. For example, if the body is burning 100% fats, RER = 0.7. If the body is burning 100% carbohydrates aerobically, RER=1.0. If the body is burning 100% carbohydrates anaerobically (flat-out sprinting), RER > 1.0. RER goes up and down depending on intensity of exercise, food intake (eating protein and/or carbohydrate increases it and extended fasting reduces it). Increasing cardiovascular fitness reduces RER.

The top diagram is a histogram of fasted RER and % fat oxidation vs. number of subjects. At the left-hand end of the histogram, there are two cyclists with a fat oxidation of 93 - 100%. At the right-hand end of the histogram, there is one cyclist with a fat oxidation of 20 - 27%.

There's a helluva difference between burning 93 - 100% fats at rest and burning 20 - 27% fats at rest. Average fat oxidation is 66%, which means that average carbohydrate oxidation is 34%. So, on average, at rest, people burn twice as much energy from fats as from carbohydrates. So, why do current "Healthy Eating" guidelines recommend almost twice as much energy from carbohydrates as from fats for everyone, including sedentary people?

As exercise intensity increases, the peak in the histogram shifts to the right as shown in the lower diagram. At 25% full work-load, mean fat oxidation is ~53%. At 50% full work-load, mean fat oxidation is ~37% and at 75% full work-load, mean fat oxidation is ~13%.

I suspect that at 100% full work-load, mean fat oxidation is 0% i.e. 100% of energy is obtained from carbohydrates when sprinting. Somebody on a very-low-carbohydrate diet like Atkins induction (~20g net carbs/day) could keel over with hypoglycaemia if they exercise for too long at too high an intensity.

As there is so much variation from person to person, you must find out for yourself your own optimum proportions of proteins, fats & carbohydrates, and these depend upon the intensity & volume of exercise you do. It all sounds rather complicated, but it isn't really.

Apply the principle of "Eat, monitor & adjust accordingly" as Toxic Toffee (ex-Muscletalk member) always used to say. The eating bit will be covered in future Blog posts. The monitoring bit doesn't necessarily involve bathroom scales.

Hang on. Isn't "dieting" all about losing excess weight? Not necessarily. Remember the old joke?
Q. What's the best way to lose 5lbs of ugly flab?
A. Cut off your head!
As your body is made of water, muscle, fat, bones, cartilage, tendons, organs, glycogen, skin etc and your scales can't tell the difference between them, losing weight the wrong way can make you less healthy. However, losing weight the right way will make you more healthy.

If you starve, skip breakfast or go for a long run before breakfast, as your body is lacking glycogen reserves & amino acids, a large amount of a corticosteroid hormone called cortisol is secreted, which increases the conversion of muscle into amino acids, then glucose. It also suppresses the immune system and weakens skin & bones.

Unless you have a lot of muscle mass to spare, it's body-fat that you should be losing, and to monitor this, either use a tape-measure around your waist, check how loose/tight your clothes are, or strip-off and jump up & down in front of a full-length mirror. As Big Les (Muscletalk Moderator) says, "If it jiggles, it's fat!".

So, what happens if you eat too much carbohydrate but your body doesn't burn it fast enough? Initially, carbohydrate intake tops-up liver and muscle glycogen stores, which increases carbohydrate-burning to compensate. The liver can store about 70g of glycogen and muscles can store about 400g of glycogen. If, despite increased carbohydrate-burning, more carbohydrate is consumed than is burned, glycogen stores continue to fill. When glycogen stores become full, RER increases to 1.0 and 100% of energy is derived from carbohydrate. Getting 100% of energy from carbohydrate means that zero fat is burned, so filling glycogen stores to the brim by eating too much carbohydrate is not a good idea if you want to burn some body-fat.

Once glycogen stores are full, any additional intake of carbohydrate beyond that which is burned passes through the lipogenesis pathway - this basically means that carbs are turned into fat - which may end up as liver fat. But there's even worse news. Fat is secreted by the liver into the blood as triglycerides. This is bad for the cholesterol particles in your blood. See Cholesterol and Coronary Heart Disease. What happens if you eat too few carbs? As stated above, a "carbohydrate-burner" taking in insufficient carbohydrates could get hypoglycaemia & keel over.

How many grams of carbohydrate per day does it take to promote lipogenesis? Someone at rest burns ~1kcal/minute. If this is derived 100% from carbohydrate, this is equivalent to 0.25g of carbohydrate/minute, or 15g of carbohydrate/hour, or 360g of carbohydrate/day. Therefore, sedentary people who consistently eat more than 360g of carbohydrate/day will probably produce significant triglycerides. People who have The Metabolic Syndrome/Syndrome-X (a high proportion of people who have excess belly fat) have increased lipogenesis and higher serum triglycerides than healthy people.

Discussing weight again for a moment, it's often said that all diets are the same, as weight loss is all about calories. This is true. See Is a Calorie a Calorie? However, body composition is determined by a combination of macro-nutrient proportions (i.e. the relative amounts of proteins, carbohydrates and fats in the diet) and the intensity & volume of exercise. Health is determined by a combination of micro-nutrient proportions (i.e. vitamins, minerals & anutrients) and exercise.

If you're only interested in weight loss, just count calories. If  you wish to lose body-fat without losing muscle mass, you need to know what proportions of proteins, carbohydrates & fats to eat (it's really not that critical, but many people get it wrong). You need to know the difference between good carbs & bad carbs, and good fats & bad fats. You need to know the best times to eat proteins, carbohydrates & fats relative to exercise (it's also really not that critical, but many people get it wrong). You need to know the difference between good exercise & bad exercise.

Continued on We are not all the same.