Jan 05 2011

Obesity Denial

It seems that for every established science there is an ideological group who is motivated to deny it. Denialism is a thriving pseudoscience and affects any issue with the slightest political or social implications. Sometimes, even easily verifiable facts can be denied, as people seem willing to make up their own facts as needed.

Denialists have an easy job – to spread doubt and confusion. It is far easier to muddy the waters with subtle distortions and logical fallacies than it is to set the record straight. Even when every bit of misinformation is countered, the general public is often left with the sense that the topic is controversial or uncertain. If denial is in line with a group’s ideology, then even the suggestion of doubt may be enough to reject solid science.

We see this when it comes to the effectiveness of vaccines, the evolution of life on earth, and anthropogenic global warming. A recent Pew poll shows that the campaign of global warming denial has been fairly successful – while the science becomes more solid around the consensus that the earth is warming and humans are contributing to this, the public is becoming less convinced.

I often encounter denial even when it comes to simple things, like body weight. You would think that the question of how many Americans are overweight or obese would be fairly straightforward, but no data is so straightforward that it cannot be distorted by dedicated ideologues. For example, in my recent post on diet a commenter made this argument:

One important fact in this discussion is that in the 1990′s the government revised the way they determine obesity and being overweight and overnight the number of people who were obese doubled. Those who want to use this as “proof” that obesity is rampant do so fully aware that they are misrepresenting the facts. In fact obesity has not statistically increased in the dozen or so years since that change and for men has decreased slightly.

There is so much wrong with this one paragraph that it will take me the rest of the post to deal with it. It is a horrendous straw man – the conclusion that overweight and obesity in this country, and generally in industrialized nations, has been on the increase is not at all based upon this one-time redefinition of these categories.

But let’s back up a bit and give some background.

Body Mass Index

The terms overweight and obesity have had various definitions in the past, but in recent years the various health organizations have settled on consensus operational definitions (for obvious practical reasons). Their definition relates to body mass index, which is a person’s weight in kilograms (kg) divided by their height in meters (m) squared.

It should be noted that BMI is a measure of weight, not fat (adiposity). BMI is used for convenience, as height and weight data are often available but more direct measures of body fat are not. It is widely recognized and admitted that BMI is problematic as applied to individuals. Muscular and athletic people may have a high BMI and not have excess adiposity, for example. Also at the extremes of height the BMI becomes harder to interpret.

But this does not mean the BMI is useless. In fact, for most people BMI correlates quite well with adiposity. In one study researchers compared BMI to a more direct measure of body fat percentage using skin-fold thickness. They found that when subjects met the criterion for obesity based upon BMI, they were truly obese by skin-fold thickness 50-80% of the time (depending on gender and ethnicity). When they were not obese by BMI they were not obese by skin-fold 85-99% of the time.

So BMI is a rough but useful estimate, good for large epidemiological studies where more elaborate fat percentage measurements are not practical. However, those who wish to deny the “obesity epidemic” have found BMI to be a convenient target for sowing doubt.

There is ongoing research into the utility of supplementing BMI with other easy measures, like waist circumference. This seems to be a more accurate measure of adiposity, and specifically risk from being overweight.

Overweight and Obese

Because BMI is a convenient measure, it has become the measure of choice in defining overweight and obesity. For children and adolescents overweight is defined as a BMI in the 85-95% percentile by age and gender, while obesity is >95% percentile BMI. For adults overweight is defined as a BMI of >=25.0 but <30.0, obese is defined by BMI >=30.0 and < 40.0, and extremely obese is defined as BMI >=40.0.

These cutoffs, like all such cutoffs for medical definitions, are partly arbitrary (they constitute drawing a line to demarcate a spectrum) but are evidence- based. This is similar to definitions for hypertension, for example. Researchers typically will set the cutoff to capture most people who are at risk for medical complications.

This is where the controversy comes into play with overweight and obesity. In 1998 the NIH decided to lower the cutoff for BMI for overweight, from 28 for men and 27 for women to 25 for both sexes. This was based upon an expert panel review of hundreds of studies. It also brought the NIH definition in line with the World Health Organization and other health organizations. The BMI 25 cutoff has now become generally accepted. The cutoff for obesity was not changed – it was and remains a BMI of 30.

Of course this means that any estimates of overweight (but not obesity) based upon the newer lower cutoff of BMI 25 would be greater than estimates based upon the previous criteria. This raised a bit of a kurfuffle, as it always seems to do when medical definitions are altered. This happened with the lowering of the cholesterol cutoff, blood pressure for hypertension, and blood sugar for diabetes.

This event in 1998 now has become a central argument in the arsenal of obesity deniers, and is evidenced by the commenter above. If you search on “obesity statistics”, on the first page you will get this apparent libertarian site which quotes a “food industry spokesman” as saying:

In 1998, the U.S. Government changed the standards by which body mass index is measured. As a result, close to 30 million Americans were shifted from a government-approved weight to the overweight and obese category, without gaining an ounce, Burrita said.

This is slightly misleading, as the obese category was not changed. But the main point is that this 1998 redefinition is being used to argue that the obesity epidemic is all smoke and mirrors. The article goes on to quote this gem from William Quick:

According to an American Medical Association report, 14.5 % of Americans in 1980 were obese, a total of 32,700,000 (based on a population of 226,000,000). If, as the above article states, the numbers of obese Americans have “doubled” in the past twenty years, this would mean there are now about 66 million of them. But thirty million of those fatties were created by a change in definition, so by the standards of 1980 [we would calculate an] obesity percentage of 12.85 percent, an actual decrease in obesity percentage since 1980.

That’s some massively flawed reasoning. Again we see the confusion of the overweight and obese categories (as with the commenter’s statement above). But also there are many false assumptions in that back-of-the-envelope calculation. Quick is mixing statistics from different sources and contexts, and the result is a mess.

What we really need is a look at the numbers over time using the same definition. Fortunately, most epidemiologists are not dolts and they get this very basic concept. In fact, it doesn’t get much more basic than this, and it would take some pretty naive incompetence to use inconsistent definitions over time.

The CDC has crunched the numbers for us, and using the modern cutoffs for overweight, obese, and extremely obese applied to BMI data for the last few decades they document a pretty steady increase in American fatness over time. Take a look at the video on the site to see this data presented graphically. Also, it is summarized in the graph here.

As you can see, the lines go steadily up – with the exception that the overweight category has decreased in the last decade. However, it seems that this is due to the shifting of people from the overweight category to the obese category, not to the normal weight category.

Of course, you could cherry pick by just looking at the overweight category. Looking at all the data, however, tells the real story.


The bottom line is that there is an obesity epidemic. The data is clear. There is always complexity to exploit, if one is motivated to sow confusion, and the obesity data is no exception.

15 responses so far

15 thoughts on “Obesity Denial”

  1. ADR150 says:

    Is the chart saying that 70+% of adults over 20 years are overweight, obese, or extremely obese?

    while I had a general sense that we’re getting fatter, that is really quite incredible to see

    its reminds me of the Slacktivist post (http://bit.ly/c89ALt) where he highlights the policy and fiscal affects of increasing rates of diabetes. whereas diabetes affects about 14% of the US population, the CDC estimates it will increase to 21 to 33%.

  2. lippard says:

    The CDC’s animated map of U.S. obesity rates over time is pretty persuasive:


  3. Dawn says:

    @ADR150: No, I think the chart is saying out of the 40% of Americans who fall into those categories, here is the breakdown. At least, I hope that’s what it is saying!

    @lippard: very interesting powerpoints. I stopped the autoplay and looked at the slides one at a time, watching how things changed over time (and was amused by the fact that there was no data from Wyoming until 1994…9 years after they started collecting data, and 2 or 3 years after all the other states had data).

  4. Ash says:

    Actually Dawn, it is almost 70% of the US population that is overweight or obese: http://www.cdc.gov/nchs/fastats/overwt.htm

  5. CivilUnrest says:

    That’s terrifying.

    I have heard (and seen compelling evidence) that simply being overweight is not as unhealthy as we’ve all been led to believe. Anyone else heard anything about this?

  6. petrucio says:

    @ADR150: Yes, that’s exactly what it’s saying.

    @CivilUnrest: There was a study with very large numbers about mortality rates and how they correlated with weight.

    Overweight people actually died slower then ‘normal’ people, but then obese people died significantly faster. It’s important to note that correlation is not causation – fit people may die more from sporting accidents, for example. But it was very interesting data with very large sample sizes.

    I am overweight, and esthetically, i do prefer myself that way. You see, I’m one of the few people who really really does NOT want to loose weight, but I sometimes think about doing it to improve my health. It was the same with smoking, but the data was clearly stacked on that one, so I quit. But that study currently makes me stay happily on my 27 BMI zone. And the 30Y revision says my engines are running just fine so far.

    But I can’t seem to find that study now. I’d like to see Novella’s input on that one, I’m still not sure what to make of it. I could easily lose weight if I wanted to, but I just don’t feel like doing it just to conform to some arbitrary healthy number.

  7. taustin says:

    There are conflicting studies, some of which suggest that average life expectancy for people in the overweight category is longer than for people in the average category, and that certain health risks are lower. I recall one saying that overweight people were more likely to survive heart attacks than average. There was also one, supposedly with a very, very large data set, saying that being less than 100 lbs overweight was not a terribly large risk, and that what risk there was disappeared by age 30. If it doesn’t kill you young, it isn’t going to, as it were.

    I remain skeptical of a “medical standard” that applies the same definitions to men as women, and ignores age and build. While BMI may work well for the majority, even the vast majority, it makes life hell for the exceptions. I have a friend who was driven out of the military for being overweight, despite being at (measured in a water tank) less than 5% body fat. He was simply that massively built and muscular.

    Just as food for thought, there is also this:


    A collection of photos of women, labeled with their BMI category. To me, virtually none of the women labeled “normal” look normal; they all look thing (some quite naturally so, some look unhealthy). Nearly all of the “overweight” women look normal, and many of the “morbidly obese” women look little more than a little chubby.

  8. Spurll says:

    @ADR150 & Dawn: If you look at the note at the bottom of the chart, you’ll see that “overweight” and “obese” are mutually exclusive categories—”overweight” is [25,30) and “obese” is [30,∞)—so you can safely add them together to get a total “overweight” tally. However, “morbidly obese” falls within the “obese” category.

  9. eiskrystal says:

    William Quick needs to look out of the window once in a while. Americans are fat. Fatter than they were 20 years ago and a simple viewing of any playground or workplace will tell you that. The idea that americans are generally thinner than they were 20 years ago is, i’m afraid, quite laughable.

    Also, even if the overweight levels were changed. All it did was start including people close to the original border of “overweight” anyway. That was a LOT of people that suddenly fell over that border. This should tell you something in itself.

  10. sonic says:

    Your mention of AGW reduces the impact of this article- it’s a bit as if you claimed that the ‘the mafia did it’ deniers are messing up the Kennedy legacy–

    1- there isn’t really a ‘scientific consensus’

    2- the evidence to support the main hypothesis is questionable-


    3- Horrific predictions are proving wrong-

    4- The ‘evidence’ includes much ‘made-up-‘ data-

    5- The promoters of this stuff (call them ‘warmest if you must) have a clear agenda-

    None of the above has any effect on the true believers- perhaps they know something I don’t- I admit I’m having a hard time finding it.

    Science anyone? (I would be willing to change my mind on this if there is any example of a model that makes accurate predictions that actually match the evidence- is there such a model?)

  11. eiskrystal says:

    All we have to do to show AGW correct is to wait. This is hardly the first mass effect on the environment by man. Or do you think the hole in the ozone layer and acid rain were also imaginary?

    Man has an effect. Just because you can pull out a few oddities doesn’t change the consensus on global warming going back what must now be almost 20 years.

    Noting your list of links. A few wordpress crank sites and minor newspaper websites? Really??…Science anyone?

  12. sonic says:

    Thank-you for your reply. I have been considering the situation and have come to the realization that all the stuff that bothers me about this subject stems mostly from one thing.
    Firstly I should say that it was many years ago that I took graduate classes in time series analysis at UC, so I am aware of the difficulties in this type of analysis (but it was a long time ago- so the specifics are rusty).
    Next- I agree that man can have an effect- in fact I would suggest that we could increase the CO2 content to double its current and one would expect to see an increase of 1/2 of a degree on average.

    What bugs me is this- it seems to me that anyone who studies the weather/ climate of Earth should be able to look at the “hockey-stick graph” and see that it is a misrepresentation of the past. The fact that this graph was put together using doubtful methods and was accepted and used as proof of hypothesis is bothersome.

    When I have questioned this graph I have been told that I have a mental illness (denialism).
    When I questioned general relativity and quantum mechanics I was shown experiments.

    Something in the difference…

  13. Diane says:


    I’m not convinced by this slideshow. I looked carefully at the photos of the women who were within an inch of my height, and the way they looked in the photos didn’t really correlate with their reported weights. I know for a fact that 160 lbs would definitely be quite overweight on my 5’5” body, and so when I see a photo of a 5’5”, 160 lb woman who doesn’t look overweight I think that the photo is misleading rather than the definition of overweight is wrong.

  14. eiskrystal says:

    Ignoring the half a degree increase you threw in… and not wanting to get too far off topic (though frankly we are already so far away i can probably see the surface of mars now) and assuming you are discussing the temperature graphs for the last 1000 years.

    1) We have actual temperature data from 1850. That shows an impressive upward shoot just by itself. If anything, the data before it actually makes the rise a little less impressive due to the medieval warm period.
    2) The data has now been calculated about 12 times using multiple methods. The graphs come out broadly the same. That is the data we have. You are free to ignore it… but it isn’t going to change.
    3) The global temperature change is actually only one of a whole host of related and identified problems from water shortages to food production to missing ice-caps that don’t rely on hockey stick graphs to make their presence felt.

  15. sonic says:

    Thank-you for that.
    Too far off-topic.
    I’ll continue to grapple.
    Perhaps later…

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