Calories, Thermodynamics, and Weight

When arguing against a specific scientific claim it is always desirable to be able to say that the claim violates an established law of science. Creationists attempt this with their argument that evolution violates the second law of thermodynamics (it doesn’t). The temptation is that such arguments are short and pithy, they seem conclusive, and they avoid the need to wade through a dense and complex set of scientific evidence and theories.

In the “diet wars” the first law of thermodynamics has been thrown around a lot. Up to now I have been aware of two camps defending their position with thermodynamic arguments. The first (and the one that I find most compelling) is the calorie in vs calorie out camp, that argues that the laws of thermodynamics apply to people too. This means that weight management must be a function of calories in (the total calories consumed by a person) – calories out (the total caloric expenditure, including metabolic processes, waste heat, exercise, and others). Thermodynamics must be obeyed and so if one wishes to lose weight they must burn more calories than they consume.

The second camp are the defenders of special weight-loss diets who claim that the type of calories one consumes significantly affects weight loss. They reject the “calorie is a calorie” mantra, and instead preach about the evils of carbs, or fats, or glycemic index. They argue that all calories are not equal because some calories are more efficient than others – they require less energy to metabolize. If you want to lose weight you want to consume inefficient calories (i.e. – more of the energy from these calorie sources is wasted as heat, or they require greater overall metabolic activity, so less is available for muscles and other uses). Therefore, they argue, thermodynamics (when efficiency is considered) favors manipulating macronutrients (protein, carbohydrates, and fats) for weight loss.

While I agree that this is a legitimate thermodynamic argument, what has not been demonstrated (either from a basic science perspective, or in weight loss research) is that efficiency has a significant effect. The bulk of weight loss studies show that total caloric intake does correlate pretty well with weight loss, at least in the short term.

I was surprised to learn that now there is a third camp, using thermodynamic arguments to claim, essentially, that dieting does not work.

Sandy Szwarc who writes the Junkfood Science blog (although billed as a “skeptical” blog she has earned a mixed reputation and seems to deny any link between diet, weight, and health) recently wrote an entry entitled The First Law of Thermodynamics in real life.  To jump to her conclusion, she writes:

The pop belief that people can simply eat less and exercise more and control their weight defies the first Law of Thermodynamics. 

To arrive at this conclusion she makes a rather bizarre and incoherent argument. Actually, reading this blog entry I had the feeling I was reading two separate articles.  The substantial middle of the entry is a mostly reasonable argument about the limitations of diet and exercise for weight loss. However, this is sandwiched in between arguments involving the first law of thermodynamics that are nothing but irrelevant straw men and non sequiturs.

It is as if she had a reasonable, but dense, argument to make about the complexities of weight control, but decided to wrap it up in a thermodynamics argument to give it more pith and punch. All she managed to do was hopelessly confuse her readers and distract from her real points.

The First Law of Thermodynamics

Szwarc writes:

As is often the case when science is dummied down into soundbytes, it becomes wrong. Such is the case in the distortion of the Law of Thermodynamics which has been simplified into the popular wisdom: “Calories in = calories out.” This simplistic adage has become something “everyone knows” to be true. It’s behind widely held beliefs that managing our weight is simply a matter of balancing calories and exercise. While that’s been used to sell a lot of calorie-reduced diets and calorie-burning exercise programs for weight loss; sadly, it’s also been used to support beliefs that fat people “most certainly must be lying” about their diets and activity levels, because otherwise their failure to lose weight would seem to “defy the Law of Thermodynamics.”

While it might seem inconceivable, this simplified maxim is little more than superstition and urban legend. To realize this fact requires us to first go back to physics class and fill in the missing half of the first Law of Thermodynamics.

The first Law of Thermodynamics, or energy balance, basically states that in a closed system, energy can neither be created nor destroyed, only transformed or transferred.

There are a number of straw men in her argument.  The first is that weight loss is all about calories and exercise, and that this is based upon thermodynamics. She is distorting this position, however. The thermodynamic argument recognizes that there are many sources of “calories out” and this is not equated with exercise. Overall physical activity can be increased without specifically exercising. When writing about this I and others point out that most calories are consumed by our basic metabolic rate. One way to increase calories out is to increase metabolism.

She confuses practical advice about what works with thermodynamic arguments. The thermodynamics are absolutely clear – matter and energy cannot vanish or be poofed into existence; the balance sheet must balance.

From a practical point of view, exercise does increase calories out, and it increases basic metabolic rate, and muscle tissue burns off more calories than fat, and fit people are likely to burn more calories just going about their day. Further, while we recognize that calories out can be increased by simply increasing metabolism, there is no safe and healthful way to do this directly. Stimulants work short term, but are not safe and cause rebound weight gain.

Her argument about a closed system vs an open system is irrelevant – another straw man.  The calories in vs calories out argument is about calories going into and out of the human system – it treats it, by definition, as an open system.

To further muddy things she writes:

Balance in an open system, like the human body, is when all energy going into the system equals all energy leaving the system plus the storage of energy within the system. But energy in any thermodynamic system includes kinetic energy, potential energy, internal energy, and flow energy, as well as heat and work processes. 

The first sentence is true – all energy must ultimately equal out or thermodynamics is violated. Her second sentence is also true – all forms of energy must be considered. But she makes it seem as if the second sentence refutes the first, which it doesn’t.

Her comment that the thermodynamic argument is used to accuse fat people of lying about their food intake is a non sequitur. It allows for the fact that there may be metabolic differences among people.  Also, it is possible that overweight people do not lie about their caloric intake, they just grossly underestimate it.

The Biology of Weight Control

Szwarc then goes on to discuss various studies concerning the biology of weight control. In this section I actually agree with most of her arguments, which essentially add up to the fact that dieting does not work. To quickly summarize her points – most people who lose weight by dieting will gain it back, it requires a huge effort of will to significantly alter one’s “natural” weight, and it is even difficult to gain weight if one is naturally skinny.

There are various reasons for this, but the major one is that our bodies evolved in a calorie-limited environment. Surviving lean times was a priority, and so when we reduce our caloric intake our bodies interpret that as starvation and reduce the basal metabolic rate to conserve energy. When we overeat our bodies interpret that as a time of plenty and takes advantage of the extra calories by increasing metabolic expenditures. This has the net effect of resisting any significant change in body weight.

While I have significant disagreements with some of the ultimate conclusions Szwarc draws from these facts, I agree with others. I agree that these well-established facts of biology make it very difficult for most people to lose weight, and that dieting almost always fails for these reasons.

If she had simply written an article summarizing this research in order to make this point, she would have had an excellent article, and one important to the public discourse on dieting.

But (even the thermodynamic nonsense aside) she also overreaches in her conclusions, mainly through cherry picking her data. She writes:

In the 1980s, Dr. Leibel had advertised to find people who’d maintained 100 pound weight losses for at least a year and a half. A colleague at the lab, Dr. Bruce Schneider, said that “he got six people and all of them were wacked.” Successful long-term losers are “monomaniacal and completely obsessed with their weight.” They’d made weight control their life, becoming extremely upset if they didn’t jog a certain number of miles a day, counting calories and constantly fantasizing about food, exhibiting every sign of dysfunctional eating behavior.

While it makes sense that obsessive-compulsive exercising is one way to keep weight off, it is premature to conclude that only the “wacked” can maintain weight loss. For example, the National Weight Control Registry tracks people who have lost an average of 66 pounds and kept it off for more than 5 years. While 90% do exercise every day, most of them get their exercise by walking. Most also made sensible changes to their eating habits.

She then turns to the notion of a set point, writing:

Dr. Leibel and colleagues at Rockefeller University later showed that when someone gains only about 10% of weight over their natural set point, their metabolisms increase by at least 16% over and above the expected increase for their size, as the body works hard to balance energy to maintain its natural size. 

Again, there is a great deal of evidence to support the conclusion that our metabolism adjusts in response to weight gain or weight loss – but this does not mean there is an unavoidable set point of “natural” weight. This cannot be the entire picture. For example, over the last 20 years average weights in this country (and the West in general) have been steadily increasing. Just watch the animated map of the US showing obesity trends.

Weight and set point cannot be only about genetics, that cannot explain the undeniable trend toward increased weight in America. It is difficult to pin down what other factors are playing a role – and everyone likes to blame their favorite boogy man. It is likely a combination of increased sedentariness and increased portion size. There may be other factors as well, including metabolic effects or changes in food choices. This is a separate and complex question. But genetics alone is insufficient as an explanation.


Szwarc’s thermodynamics argument is worthless and misleading – an unnecessary distraction from her real points, which are themselves a mixed bag. I agree with her that diet and exercise alone are not sufficient to explain weight gain or loss, as we also need to consider major changes in metabolism. I also agree that will power is not sufficient for most people to make long term changes to their weight. It is simply too difficult to maintain. I agree that the evidence shows that dieting often does not work. And I agree that genetics has a huge influence on our weight and body type – not everyone can and should be skinny.

However, I disagree with her ultimate conclusion that any conscious attempt at weight control is hopeless (unless you are a fanatic) and we are slaves to our genetic set points. Recent history belies this conclusion.

Rather – I would conclude that weight control is difficult, but not impossible. In addition, I believe that the popular weight loss industry is making the problem worse by distracting the public from those strategies for which there is at least some evidence of efficacy and focusing on minute, short term, and probably insignificant effects from manipulating macronutritent proportions.

The evidence suggests that long term weight loss is possible through lifestyle changes. Increasing daily activity and regular exercise is helpful. People have difficulty estimating what they eat, so keeping a diary is also very helpful.

Further, if will power is not the answer because it is too difficult to maintain, then it would seem that the answer is to make lifestyle changes as easy as possible so they can be sustained. From a public health point of view, healthful choices need to be made easier. The real lessons from the studies that Szwarc cites is that long term weight control requires sustainable strategies, not quick fixes and not magical diets.

Posted in: Public Health

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16 thoughts on “Calories, Thermodynamics, and Weight

  1. David Gorski says:

    The problem with Sandy Szwarc is that she is one-sided and tends to use crank arguments. She’s not as obvious as a lot of denialists. I admit that it took me a few weeks of reading her blog to realize the problem. I had found her blog because it was praised by so many, but as I read it I got an increasingly unsettling feeling that all was not right with her arguments. For one thing, when it comes to weight and cholesterol, I can’t recall her ever conceding that there is a detrimental effect on health due to obesity, except minimally and grudgingly. For another thing, she attacks pretty much any major study that finds a health risk due to obesity or diet, and I can’t recall her ever expressing skepticism over studies that fail to show a correlation between health problems and obesity. Third, as you mention, she cherry picks evidence to support her case and does not give adequate due to evidence that does not. Fourth, she attacks a lot of straw men about the science about diet and exercise, always in the name of arguing that obese people simply cannot lose weight through diet and exercise. As you also point out, losing weight can be incredibly difficult, but it’s far from impossible. Ms. Szwarc always downplays the risks of being obese.

    She abuses science sometimes to make her point. As you point out, her post could have been quite reasonable if she had not tortured thermodynamics in the way that she did. All the thermodynamics argument did, IMHO, is actually to weaken her article. If she had just said that “energy out” means metabolism plus activity and that metabolism is the major contributor to that, there would have been nothing much to argue about. But, nooooo. She had to add the thermodynamics handwave and claim that the “complex system” of metabolism made the application of the first law of thermodynamics so very, very complicated, and make a big deal of the difference between an open and closed system that had no relevance to the argument she was trying to make, all in an effort, it appears to argue weight loss is impossible through diet and exercise alone. I exaggerate, but not by much.

    A bit of Ms. Szwarc’s attitude is captured here:

    Szwarc’s written works have also included a series of articles published by the Competitive Enterprise Institute, a Washington D.C. libertarian think tank. Her articles, published between March 2004 and January 2006, sought to convey reassuring messages on mercury in fish and from power plant emissions.”Fishy Advice: Why We Need not Fear Methylmercury in Fish”, was the headline of one. “The fear factor: Benefits of sale, healthful fish lost in sea of methylmercury concerns” was the headline on another.[6]

    She has written several article mitigating the effects of mercury toxicity on humans,[7][8][9] disputing the scientific research which has shown that methyl mercury harms consumers of fish and that mercury spills in schools are harmful to children. She has argued that United States’ Environmental Protection Agency moves to curb mercury emissions were excessive.[10]

    She has also written to argue against legislation restricting or banning phthalates, asserting that the chemical poses no threat to the health of infants.[11], and genetically modified organisms as a danger to future agriculture.[12] On her former website,, she has also published articles, including one claiming contracting mad cow disease is essentially no threat to humans.[13]

    In a review of a book on biotechnology by Henry I. Miller and Greg Conko, Szwarc railed against what she described as the “‘absolute safety at all costs’ perspective that’s been skillfully fueled by scares and misinformation from special interests. As a result, foods and technological developments that can and are bettering our lives and can save lives, are being maligned, feared and resisted far out of proportion to their potential risks. The result of overly-cautious, inaccurate tenets is regulatory policies rife with blunders and inconsistencies that hurt consumers, most of all the poor and disadvantaged. We not only deny ourselves better choices, as well as perfectly safe foods, we deny them to others who may more desperately need them”.[12]

    “Virtually every food and health fear today fits this description: the “obesity crisis,” pesticides in fruits and vegetables, mercury in fish, mad cow from beef, hormones in milk, “bad” fats in snacks, refined sugars in treats, arsenic in water, and the countless other unfounded scares bombarding us. But understanding how fears take hold, what’s behind them, and what they’re doing to us, is the first step towards helping ourselves,” she continued.[12]

    She’s also cited approvingly by The International Network of Cholesterol Skeptics, has said that “far more young people are dying from anorexia than any are from being fat,” and has been known to use abuse Godwin’s Law in comparing public health officials and scientists who warn of the health problems due to obesity to Josef Goebbels. Overall, she takes the science showing that weight loss can be very difficult due to metabolic issues and gussies it up to try to argue that weight loss is impossible with diet and exercise alone, and–oh, by the way–go right ahead and eat that extra donut. Or two. No problem.

    I tend to look at Ms. Szwarc as a cleverer, less obvious version of Steve Milloy or Michael Fumento. To her, everything showing a problem from industry (particularly the food industry) is “junk science,” as is any study showing a correlation of health problems with diet or obesity. No health scare (not even mad cow disease or pesticides) is legitimate, nor is any study showing the rise of the number of obese people. In fact, I seem to have recalled her arguing in some cases that obesity can be more healthy.

  2. overshoot says:

    The thermodynamics are absolutely clear – matter and energy cannot vanish or be poofed into existence; the balance sheet must balance.

    As far as I can tell, her argument isn’t against matter or energy vanishing but very particularly that it can “be poofed into existence:” that one can expend more calories than the diet includes and still gain girth.

    The importance of the distinction is that it takes all of the arguments about efficiency and so on totally off the table. Unless one presumes an “efficiency” of greater than 100%, there’s simply no way to reach her objective: an excuse for bulking up while still following diet and exercise programs.

    And let’s face it: an excuse really is what she’s after.

  3. James Fox says:

    I’ve found reading Scwarz’s blog an interesting, sometimes informative and sometimes frustrating adventure. I wish there was someone who’d address nutrition diet and science issues with the same level of enthusiasm and more willingness to weigh the available evidence. Ms Scwarz is a very good writer which makes her (one sided) blog all the more appealing in the sea of poorly written schlock available on the internet. Except of course the non schlocky stuff at Science Based Medicine, NeuroLogica, Respectful Insolence… .

  4. Harriet Hall says:

    Haven’t these people noticed that in famines everybody loses weight? Did they notice that in the concentration camp liberation photos every prisoner was emaciated? Have they considered the movie stars who gain and lose weight on command to fill the requirements of their roles?

    The principle is simple; it’s only the execution that is difficult.

    My daughter adopted a labrador retriever that was overweight at 125 pounds; she fed him measured amounts of food as prescribed by the vet, and a year later he was a healthy 75#. And has stayed there on a maintenance diet. There is no way this kind of program wouldn’t work for any human if we could control human intake as easily as we can control a dog’s food.

  5. James Fox says:

    So Harriet, was your mention of the concentration camps a veiled reference to something Nazi by way of argument???

    Sorry, couldn’t resist.

  6. Harriet Hall says:

    Who, me? I was thinking of Andersonville. See picture of Union soldier who survived:

  7. HCN says:

    We also have a local case to remind us of the results of starvation:
    “Long denied ever withholding food or water from the girl, but admitted locking her in her room.

    “She conceded she had done that, admitted it was wrong and agreed not to do it again,” said Thomas Shapley, spokesman for the Department of Social and Health Services.

    Instead, the abuse worsened over the next three years, and when police were called again Aug. 13, the girl, now 14, looked pale, weighed 48 pounds and looked half her age. This time, she and her brother, 12, were removed from the home and placed into foster care.”

  8. David Gorski says:

    Who, me? I was thinking of Andersonville.

    Actually, Andersonville was a military prison used to house prisoners of war, not a concentration camp. A subtle, but real difference.

    Sorry, couldn’t resist being pedantic. I’ll stop. For now.

  9. Great post, Steve.

    Calories in always equal calories out. But all isocaloric diets aren’t necessarily equally effective for weight loss.

    Some sources of calories are more satiating. If your diet is based on highly satiating foods, you may spontaneously take in less energy and feel less hungry.

    I think there’s pretty good laboratory evidence that high-fiber carbs and lean proteins are especially satiating. How that plays out in the real world over the long term is much less clear.

  10. Jules says:

    Ah, JFS…if you read it regularly you’ll find that it’s misguided, but not malignant, in the sense that she doesn’t use pseudoscience to counter science, just badly-done-and-poorly-thought-through-arguments to counter science. I read it regularly myself, if only for the entertainment value. Her deconstructing of scientific studies is so ludicrous it makes homeopathy sound scientific by comparison.

    I especially loved her assessment of the study that showed 1 hour of walking a day was needed to keep off weight. Not surprisingly, she begged to differ, and proceded to show that there was no appreciable difference.

    Somehow it escaped her that losing 10% of your weight when you have a BMI of 32, while impressive, still leaves you with a long way to go to get healthy.

  11. MJW says:

    Having recently lost 85#s and still losing, I can say that for me at least, it’s been all about the limiting of what I eat. It still is. It’s going to be hard for me not to yo-yo around about 10 pounds when I try to get to the maintenance part of it, but I certainly feel the difference. I’d like to see what she thinks happens to your body when you quit smoking.. I gained 30# just from that, I guess it was the lack of nicotine, not the extra food I was eating..

  12. MJW– Good for you for losing so much! That’s an awesome commitment you’ve made to your health, and you should be really proud. I’m also trying to limit what I eat, and it’s not easy!

  13. Owen says:

    >>> For example, the National Weight Control Registry tracks people who have lost an average of 66 pounds and kept it off for more than 5 years. While 90% do exercise every day, most of them get their exercise by walking. <<<

    That’s ever-so-slightly misleading. The NWCR tracks lots of people, and on average they have lost 66 pounds and kept it off for more than 5 years. Your phrasing makes it sound like they ONLY track people who’ve lost at least 66 pounds for more than 5 years. Pedantic? Yes. Can I help myself? No.

    I also think your “most of them get their exercise by walking” slightly understates the facts. You make it sound like it’s not a big deal. I would argue that actually, exercising for an hour every day *is* a big deal, whether it’s walking or otherwise. It’s a significant commitment (certainly in my lifestyle), and is very hard to maintain. Perhaps it doesn’t make you “monomaniacal and completely obsessed”, but I don’t think it warrants the way you downplay it here.

  14. CarolynS says:

    I’d like to speak up in support of Sandy Swzarc’s blog, which is often excellent and very insightful about the problems of some of the scientific articles that garner a lot of headlines and also about the merits of some studies that get ignored because they don’t quite suppport the prevailing orthodoxies. Yes occasionally she gets carried away but so do lots of others. I am pretty well trained and very well published (in respectable journals) in several of her areas of interest and I find her information generally reliable and her insights sometimes really penetrating. She always gives the references and you are free to go check them out yourself. I have found some really valuable information through her blog that I would otherwise have overlooked. Incidentally, what is so wrong abou t saying that more young people are dying from anorexia than from being fat? Yes perhaps a tendentious statement but seems quite likely to be true on the face of it. The case fatality rate for anorexia is extremely high.

    Obesity and weight regulation are complex topics, and people quite readily turn to personal experiences and beliefs instead of science. In a science-based blog, it’s kind of striking. The National Weight Control Registry is a small number of people and almost completely based on self-report, so it’s wise to be careful about using it to draw sweeping conclusions.

  15. David Gorski says:

    I’d like to speak up in support of Sandy Swzarc’s blog, which is often excellent and very insightful about the problems of some of the scientific articles that garner a lot of headlines and also about the merits of some studies that get ignored because they don’t quite suppport the prevailing orthodoxies.

    I used to think Sandy was a real skeptic. I still think she is for anything other than topics of obesity and cholesterol, where her position is always–and I do mean always–to defend the position that fat isn’t a problem in the diet and that obesity is just ducky (more or less). See:

    Ms. Szwarc is also listed as an expert for the Competitive Enterprise Institute; so her defense of the food industry at every opportunity is, sadly, not surprising:

    She’s also been known to take a “what, me worry?” attitude to mercury in fish and claiming that Mad Cow disease is no threat to humans. Basically, I’ve come to the reluctant conclusion that she’s a food industry apologist.

  16. CarolynS says:

    I know what you mean but that doesn’t mean her science is poor. As to the obesity problem, haven’t you noticed that there is a pretty large cadre of people who will not accept anything that suggests maybe obesity isn’t always so bad and who get violently upset when research shows (e.g.a big meta analysis in the Lancet a few years ago) that so-called “normal weight” people with coronary artery disease have higher mortality rates than “overweight” and even “moderately obese” patients? Yet no one calls these people out as denialist cranks. I honestly don’t see Sandy leaning any farther in the one direction than a lot of people do in the other.

    I’m not saying research like the Lancet article in question (very respectable, from the Mayo clinic) is the final answer. All I am saying is that there is a lot of evidence similar to the Lancet article out there and that some people (very very often funded directly or indirectly by drug companies) simply reject or ignore all evidence suggesting that obesity is not necessarily the most dire threat faced by humanity. This really distorts the science and I think leads to making Sandy look like she is further out on a limb than she really is. OFten what she is pointing out is simply the complete lack of evidence for some tendentious statement.

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