Sunday, December 12, 2010


This from psipsina:

One of the more irritating things about die-hard proponents of low-calorie weight loss diets is how they talk about “the laws of thermodynamics” as though they have any idea what they actually mean, or how they might be applied to human nutrition.  Usually, I struggle mightily against the sin of arrogance, but I must say that when I read what passes in the press for nutrition writing, I am confident that I understand the laws of thermodynamics, as well as all the other laws of physics, better than most journalists do.

So, in today’s edition of Dumb Things the Diet Dictocrats (tip o’ the hat to Sally Fallon for the term Diet Dictocrats) Say, I am going to take on the tired notion of “calories in, calories out.”  In so doing, I hope I can make amends to the first law of thermodynamics for the sins that have been committed in its name.  I don’t use the word sins lightly; what else can you call it when someone like Jane Brody, who actually has a degree in biochemistry and should know better, advises the American public to consume exactly that diet that is most likely to lead to heart disease, diabetes, stroke, cancer, autoimmune disorders, and a host of other grievous ills, and on no better evidence than a fundamental misunderstanding of energy use and storage?

I am picking on Brody not because she’s any more egregious than any other writer, but because this article of hers provides an example of just exactly where the popular understanding of calories goes awry.  Here she “explains” to the reader how thermodynamics apply to the human body:
With respect to weight gain and loss, the laws of thermodynamics can be translated as: Calories consumed must be used or they will be stored as body fat.
So far, I have little quibble with what she says, though, as you’ll see below, I think it would be more accurate to say that “calories consumed must be disposed of.”  But before I go much further, I have to say that a surefire clue that a nutrition writer is a little fuzzy on the subject of thermodynamics is when he starts talking about the laws, plural, of thermodynamics.  What he means is the first law, which states that the amount of energy in a closed system does not change, the implication being adding energy to such a system results in a net increase in energy unless an equal amount of energy is subtracted from the system.  This law is often expressed as Energy is neither created nor destroyed.  The zeroth (yes, there really is one), second, and third have little to do with the total energy of a system.

So if I don’t fundamentally disagree with “calories in, calories out,” what is my beef?  The problem is that writers like Brody don’t understand the “calories out” portion of the equation.  And this misunderstanding is based on at least three fundamental myths, assumptions, or oversimplifications about how calories are expended.

Myth 1:  Calorie burning is 100% efficient.

Brody’s first poorly justified assumption is that the human body burns calories 100% efficiently and never wastes any – any that are not burned are stored as fat.  Indeed, in the article cited above, she goes on to say:
The body does not waste energy, no matter what its source.
This is an assumption, not a fact, and it is an assumption that is easily refuted.  The popular press delights in talking about the so-called dangers of ketosis, the metabolic state induced by significant carbohydrate restriction.  And yet they do not seem to catch on to the fact that the very process of ketosis results in a waste of body energy!  Let me say that again:  ketosis is a process that results in a waste of energy.  An analogy might be helpful – if you burn a log of wood for a certain amount of time, you will release or use energy in the form of light and heat, and you will probably end up with a large chunk of black stuff called charcoal.  You could throw out this hunk of charcoal.  But the charcoal still has energy, as anyone who has ever used a charcoal grill will understand, so you could also burn the charcoal and cook a steak over it.

The body’s metabolism of fat is very much like this.  When fats are burned, a by-product called ketones is produced.  Ketones are incompletely burned fat molecules, and like charcoal, they still contain some energy.  Some of the ketones can be and are burned for further energy; the heart and brain in particular will suck up ketones to use as fuel whenever they are present.  But if more ketones are produced than can be used, as is the case when fat is the primary source of dietary calories, the body excretes the unused ketones in the urine, breath, and sweat.  The body does not have a mechanism for storing excess ketones for later.  It’s like burning wood and tossing out most of the charcoal because there’s no place to keep it – a waste of energy.  And if you are overweight, wasting energy is exactly what you want to do.

Myth 2:  Basal metabolic rate never adjusts.

A person’s basal metabolic rate is the number of calories required just for low-level life processes – breathing, heartbeat, digestion, brain and nerve functions, and so forth.  You can think of it as the number of calories you’d need if you spent 24 hours lying very still.  The total number of calories a person expends in a day equals the person’s basal metabolic rate plus the number of calories expended in activities (plus, as we saw above, calories wasted by the incomplete burning of fat).
The way most popular nutrition writers understand this, a person’s basal metabolic rate (and for that matter, the number of calories expended by a given activity) does not respond to increased caloric intake.  Oddly, though, these same writers will easily grant that basal metabolic rate does respond to decreased caloric intake.  In fact, they use this phenomenon, which is well documented, to explain the failure of most people to lose significant amounts of weight, or keep the weight off, on low-calorie diets (which makes you wonder why they continue recommending such diets.  But I digress).  Our bodies, they say, evolved to store weight easily in times of plenty and get rid of it slowly in times of famine.  When you diet, they say, your body thinks a famine is impending and holds on to every last calorie it can.  People whose bodies did not work this way, they reason, would have failed to make it to reproductive age during famine; so we have our famine-resistant ancestors to thank for the inheritance of a gene that makes it hard for us to lose weight.  This is sometimes known as the Thrifty Gene argument.

This argument always makes me think that they don’t understand evolution any better than they understand thermodynamics!  I happen to think that the theory of evolution is just about the most brilliant product of the mind of Western man, but the problem with explaining our current condition by recourse to evolution is that all we know is that at some point in human history, conditions favored genes that are prevalent in our genome today.  Exactly what those conditions are is usually nothing but speculation, and you can almost always spin an equal and opposite story.  (This also drives me nuts when it’s used to explain the psychosocial differences between men and women, but again I digress.)  In the case of metabolism, an equal and opposite story would be that, in times of plenty (and surely there have been times of plenty in our evolutionary history – famine is a relatively recent occurrence in human history, tied to the development of agriculture and the subsequent dependence of humans on very small numbers of different crop species), it would be a disadvantage for our ancestors to gain more than a few pounds.  An obese hunter-gatherer would have a disadvantage in chasing prey or in running away from predators.  Furthermore, we know that obesity is associated with debilitating conditions like heart disease and diabetes.  Therefore, the obese would’ve been eaten by massive carnivores or died of heart attacks or diabetes complications and would’ve failed to reproduce.  Therefore, goes my story, our bodies have evolved to waste calories by kicking up our metabolisms when food is plentiful.  Let’s call this the Spendthrift Gene argument.

Is my equal and opposite story true?  I have no idea, any more than an honest proponent of the Thrifty Gene argument will claim to know if their story is true.  These stories are both what the ancient Greeks called “likely stories,” stories that “save the phenomena,” i.e., account for observations in a more or less plausible way.  We do observe that people burn fewer calories when they consume fewer calories, and – the dirty little secret that the low-calorie people don’t tell you, maybe because they don’t know it themselves - we also observe that people who consume more calories actually burn more calories, but only on low-carbohydrate diets.  I am not going to go into a thorough review of the research here; Gary Taubes devotes a good portion of Good Calories, Bad Calories to an examination of the research.  Let’s just say that studies have been done where participants were put on high-fat diets containing 3,000, 5,000, or even 10,000 calories per day and maintained stable weights or even lost weight without increasing their activity levels.

Myth 3:  Anything that can be burned will be burned immediately or stored to be burned later.  There are no other choices.

We consume three nutrients that can be burned, carbohydrates, proteins, and fats.  And in fact, carbohydrate is good for nothing but burning.  It’s like gasoline – you can either ignite it with a spark and burn it now, or you can store it in your gas tank to burn later.  And with carbohydrates, it is true that if you consume more than your body can use, your body saves them for later.

Protein and fat, however, have a host of uses in the body in addition to generating energy.  Protein is used to build muscle cells, to create and repair cell membranes in all cells, and to create enzymes that make it possible for all your body functions to occur at the relatively low temperature of 98.6 degrees.  Fat transports certain nutrients that are not soluble in water, acts as a precursor to a number of hormones, insulates neurons to ensure that electrical charges are carried properly, and, like protein, is used to create and repair cell membranes.  Furthermore, fat and protein can both be broken down and recombined into whatever form the body needs.  So you might consume muscle protein from a cow, and the body might break it down and rearrange it to make a digestive enzyme, or incorporate it into the membrane of a brain cell, or use it to make the red blood cell protein hemoglobin.  Protein and fat are like wood – you can certainly burn it for energy, but you can also use it to build a house, or grind it up and make paper out of it.

It should be obvious that we use our food for something other than burning – if it were not, we’d collapse into little unorganized puddles of organic compounds (oh, hey, that’s the second law of thermodynamics, if you’re interested).
So the next time someone tries to wave the laws of thermodynamics in your face as an explanation of why low-calorie diets are better than low-carb diets, have a little fun with them.  Ask them to name the laws of thermodynamics and explain to you how they are applied to human metabolism, or better yet, ask them exactly how calories out are calculated.

To read the full article, click here.

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