Jun 232010
 

In my last post on Gary Taubes and his book Good Calories, Bad Calories, I stated that I would do a chapter-by-chapter critique of the book, starting with Chapter 14, “The Mythology of Obesity”.  In this chapter, Taubes begins to create a mystery that doesn’t actually exist.  He does this through a combination of logical fallacies, selective quotation of out-dated scientific data, and leaving out existing data that conflicts with his statements.

Taubes opens the chapter with this sentence: 

“Critical to the success of any scientific enterprise is the ability to make accurate and unbiased observations.”

He then goes on to say:

“…if the initial observations are incorrect or incomplete, then we will distort what it is we’re trying to explain.”

Taubes is correct in these statements.  Unfortunately he doesn’t follow his own advice.  He notes the hypothesis that obesity is due to excess calorie consumption and/or inadequate physical activity, and then says that this hypothesis fails to explain the evidence and observations. 

However, what Taubes fails to realize is that it only fails to explain the evidence and observations when you leave out important information regarding that evidence or those observations.

Taubes’s First Big Boo Boo

Taubes makes his first big mistake on the very first page of this chapter.  He writes:

Lean people will often insist that the secret to their success is eating in moderation, but many fat people insist that they eat no more than the lean – surprising as it seems, the evidence backs this up – and yet are fat nonetheless.  As the National Academy of Sciences report Diet and Health phrased it, “Most studies comparing normal and overweight people suggest that those who are overweight eat fewer calories than those of normal weight.”  Researchers and public-health officials nonetheless insist that obesity is caused by overeating, without attempting to explain how these two notions can be reconciled.

The last statement in that paragraph is blatantly false.  These two notions have been reconciled over and over again in numerous studies.  It is well established that overweight people underreport their food intake on average.  In fact, there is a huge volume of literature of on this…so huge that it is surprising that Taubes missed it all.  The underreporting is quite severe.  One study comparing obese twins to their non-obese twin counterparts indicated underreporting of 764 calories per day.  Another study indicated obese subjects to be underreporting their calorie intake by over a thousand calories per day.  This is just a fraction of the data that is out there.  Yet, Taubes selectively quotes out-dated research that relied on self-report of food intake.  Taubes’s reliance on out-dated and low quality data will be a consistent theme through the remainder of his book.

The phenomena of underreporting is verified when you supply overweight people with the amount of calories they claim to be eating.  In one study, women who claimed to be eating 1200 calories per day were supplied with that actual amount of food intake.  What happened?  They lost 1.7 pounds per week.  George Bray reported on a similar clinical experience.

My own clinical experience also verifies this.  For example, we had one individual who was not losing weight.  She swore to the dietitian that she was following the program.  One day, her husband came into the dietitian session with her.  He ratted her out and said she was eating 8 tablespoons of peanut butter per day and wasn’t recording it in her food log.  That’s over 800 calories per day of food intake that she wasn’t reporting.  It is no wonder why she was not losing weight.  This is not to say that everyone who underreports food intake is blatantly lying about it.  Many people simply do a poor job of estimating their food intake.  But the fact is, people underreport their food intake.

Taubes, through selective cherry-picking, tries to create a mystery where there is no mystery.  He calls the idea of energy imbalance a “hypothesis”, yet fails to consider not only the data mentioned above, but all of the controlled studies that demonstrate experimental overfeeding to create weight gain.  Researchers insist that overeating causes obesity because that’s exactly what the data shows, despite Taubes’s attempts to spin it otherwise.

The “Carbohydrate or Calorie” False Dichotomy

Taubes moves on to discuss data from the National Health and Nutrition Examination (NHANES) survey.  From 1971 to 2000, this data showed an increase in calorie and carbohydrate intake (as a percentage of calories) in the U.S. population, while fat intake decreased.  Taubes then states:

This increase in energy intake…was “attributable primarily to an increase in carbohydrate intake.”…The NHANES data suggest that either calorie or carbohydrates could account for the increase in weight…

Taubes creates a false dichotomy here by asserting that either the increased calorie intake, or the increased carbohydrate intake, was responsible for the weight gain.  However, it’s not “either/or” because the two are not independent of each other.  The increased carbohydrate intake IS the increased calorie intake, so you cannot separate the two.  Taubes creates a dichotomy where none exists.

Anecdotes and Newspaper Articles are Not Scientific Evidence

Taubes goes on to discuss physical activity.  He talks about the “exercise explosion” of the 1970’s and 80’s, implying that Americans were more active than ever.  However, what does he cite to support this?  Some anecdotes and newspaper articles from the New York Times and the Washington Post.  He also cites statistics on the revenues of health clubs.

It is absurd to imply that physical activity is high based on some newspaper articles and gym revenues.  For example, many people join gyms but don’t go, or go infrequently.  And no matter how many Americans were supposedly partaking in the “fitness revolution”, it is not statistical evidence of how truly active Americans were.   Also, formal exercise only represents a small portion of total daily energy expenditure.  When it comes to physical activity, we are concerned with all physical activity throughout the day, not just formal exercise.  Gym memberships and the “fitness revolution” are not indicative of 24-hour energy expenditure.

If you look at the science rather than anecdote, you get a different picture.  While there isn’t good survey data regarding physical activity from the 1970’s and early 1980’s, the CDC does have data on leisure-time physical activity trends from 1988 to 2008:

Now, this is just leisure time physical activity, and not 24-hour activity.  However, you can see that the trend was mostly flat, with a slight downtrend in this decade.  This data indicates that 1/3 of Americans participate in no leisure time physical activity at all.  Taubes’s numbers on gym memberships are meaningless, and his claims of a “fitness revolution” do not hold when you look at the data.

There is also data out of the Minneapolis-St. Paul metropolitan area between 1980 and 2000.  The percentage of individuals engaging in physical activity for 30 or more minutes, at least 5 times per week, was only 8-12%.  Only 1% participated in 60 minutes daily.  While this is not national data, the results were similar to what has been observed on a national level, and contradict Taubes’s implication of an “exercise or sports epidemic” in America.

There is also data estimating the cost of mechanization (dishwashers, elevators, cars, etc.) to our daily energy expenditure.  It is estimated that we expend an average of 111 calories per day less, which, if not compensated by lower food intake, would result in substantial weight gain over many years.

In the usual fashion, Taubes creates a physical activity paradox where none exists.

The Poverty/Obesity Relationship:  Not A Contradiction After All

Taubes moves on to address another apparent contradiction…that obesity rates tend to be higher among the poorest members of society.  Taubes considers this a contradiction for two reasons.  First, he presumes that the poorest members of society are also the hardest-working, have less access to labor-saving devices, and thus are the most physically active.  Second, he presumes that they are undernourished and do not eat very much.

Of course, these are both assumptions.  Interestingly, Taubes criticizes advocates of the thrifty-gene hypothesis for making assumptions.  Perhaps Taubes should take a look at his own assumptions.

When you actually investigate the scientific data, you will find that Taubes’s assumptions do not hold.  First, let’s look at the presumption of low calorie intake.  There is a wealth of data that shows that the calorie intake of people living in poverty is not low.  In fact, people in poverty are more likely to consume energy-dense foods, because energy-dense foods are much lower in price.  There is an inverse relationship between the energy density of foods and price.  Here is a chart showing food prices from Seattle supermarkets in 2006:

 

You can see that the least expensive foods are both the fats and the refined carbohydrate foods, so one cannot simply point a finger at carbohydrates here.  In fact, there is a several thousand percent difference between the cost of vegetable oils and sugars compared to fresh produce.  It is very easy to overconsume calories when eating energy dense foods.  In fact, the energy density of foods plays a role in regulation of food intake, and high energy-density foods lead to passive overconsumption (meaning you consume more calories without noticing it, or without adequate feelings of fullness).  For a given volume of food, the greater the energy density of your diet, the more calories you will eat.  Thus, you can actually spend less and eat more.

People in poverty are more likely to underreport their food intake.  They are also  more likely to skip breakfast, which can result in appetite dysregulation and greater daily energy intakes (interestingly, adolescent breakfast skippers also have lower carbohydrate intakes).  Also, low-income urban neighborhoods have a high density of small food stores, which carry mostly energy-dense foods.

Let’s also look at the presumption of high activity.  This does not hold when one looks at the data.  According to NHANES, leisure time physical inactivity is higher in people below the poverty line compared to people above the line.  This is particularly true among women, where obesity rates also tend to be higher.

On top of all that, Taubes fails to consider that obesity rates for higher socioeconomic classes increased at a higher rate than lower socioeconomic classes from 1976 to 2008.

The bottom line is that poverty does not mean chronic energy deficiency or high physical activity.  In fact, impoverished populations with true chronic energy deficiency have almost no obesity.

Pima Problems

Taubes continues to get it wrong when he moves to discuss the Pima Indians, again relying on old data from the 1800’s and eary 1900’s, including journals and anecdotes rather than rigorous scientific research.  He discusses how the Pimas went from food abundance to poverty when placed on reservations, along with a corresponding rise in obesity.  He implies that it could not have been due to an increase in energy intake or a decrease in physical activity.  His support for that?  Anecdotes from anthropologists.  Taubes relies heavily on anecdotes from anthropologists Frank Russell and Ales Hrdlicka.  Taubes comments how obesity was most prevalent among the Pima women, who also (supposedly) “worked considerably harder than the men”, and mentions how Russell was not particularly confident that the Pima were no longer active (I’m not sure how Taubes can infer Russell’s level of confidence from written words).    He mentions the low fat intake of the Pima (24% of calories, according to data from the physician Frank Hesse), and the high intakes of refined flour, sugar, and canned fruits.  The implication, of course, is that it’s the carbohydrates causing the obesity, not elevated energy intake and/or reduced energy expenditure.

When one looks at more modern, higher quality scientific data, we get a different story.  There is a group of Pima Indians living in a remote region of the Sierra Madre Mountains in an area only recently accessible by road.  These Pima have experienced little change in environmental conditions, and continue to lead the traditional lifestyle of the Pimas of the 1800’s.  A number of studies have compared these Pima Indians to the U.S. Pima Indians living on reservations.  Rates of obesity are dramatically lower among the Mexican Pimas compared to the U.S. Pimas, while physical activity levels are 2.5-7 times higher.  Direct measurements of energy expenditure using doubly-labeled water have shown the energy expenditure of the Mexican Pimas to be 600 calories per day higher than U.S. Pimas.  The Mexican Pima Indians have a diet of over 60% carbohydrate, and around 26% fat.  Estimates of the traditional Pima diet before the influx of the white man place the carbohydrate intake even higher at 70-80% carbohydrate.  So much for carbohydrate causing obesity!

Chapter 14:  Nothing But Mythology

The bottom line is that the vast majority of the information in chapter 14 is misleading and based on very selective reporting of mostly old, low quality data.  Unfortunately this journalistic style of Taubes continues through the rest of the book.  Supposedly Taubes did 6 years of research for this book, yet it took me only a few days of PubMed searches to find better research.  Chapter 14 is more an exercise in confirmation bias than true scientific inquiry.

I will discuss Chapter 15, “Hunger”, in a future blog post.

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