According To Lousy Media Coverage, A New Obesity Study Has Found That Every Big Mac You Eat Is Raising Your BMI By 0.03 (But Don't Panic, Because It's Not Actually True)

Surprise, the media coverage of a new obesity study is misleading and inaccurate and I'm explaining why.

Feb 14, 2014 at 12:00pm | Leave a comment

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BRB just bringing this burger to heaven.

You may have read something in the past few weeks about the influence of fast food on your weight, as described by a new study out of the University of California, Davis. And you might have panicked a little -- or at least raised an eyebrow -- after reading all the reporting that each fast food meal is measurably raising your personal BMI. 
 
The actual study, published in the February 3 issue of the Bulletin of the World Health Organization, attempts to forge a connection between the deregulation of fast food industries and increasing Body Mass Index (BMI), specifically as they occur in “high-income” countries like the US. The study’s authors drew data on fast food transactions from a global market database, and compared it with BMI rates to demonstrate how a lack of government oversight in the proliferation of fast food outlets is contributing to increasing numbers of overweight and obesity.
 
SNORE, right? It’s not the sexiest study ever. The main interest comes from the fact that it is the first study to look at the number of transactions instead of fast food outlets themselves (not joking, one such “ecological” study found that the density of Subway sandwich shops was a positive predictor of increased BMI) and so the authors had the opportunity to break down the BMI effect to an overall increase of 0.03 per fast food transaction.
 
But that's kind of dull. So predictably, the media coverage of this study has reframed the results to fit the comfortable cultural obesity narrative we’re already familiar with. 
 
For example, the NBC News headline on this study roundly declares, “STUDY SHOWS EXACTLY HOW FAST FOOD PACKS ON POUNDS” and then fails to deliver on this promise, because the study as reported does not show “exactly how” fast food "packs on pounds." The Daily Mail does not disappoint either, proclaiming, “Still fancy that burger? Every fast food meal you eat bumps up your BMI by 0.03 points.” 
 
Indeed, far from showing the precise process by which fast food makes people fatter, or demonstrating an individual BMI increase per each hamburger consumed, the researchers themselves found their results raised as many questions as they answer. From the study itself:
Our study shows the fast food consumption is independently and positively associated with mean BMI in high income countries. While the consumption of soft drinks explains a small proportion of the variation in the association between fast food consumption and BMI, the intake of animal fats and total caloric intake do not seem to be significant mediators of the association. This is puzzling. The fat and calories in fast food meals are usually blamed for the unhealthful effect of fast food. Although we cannot exclude the possibility of measurement errors, factors other than calories and fat content may explain why fast food makes people fat. Researchers need to investigate, for example, the metabolic effects of long-term exposure to fast foods produced from the meat of animals fed on corn, kept in confinement and exposed to excessive fertilization. Researchers should also examine the health effects of a poor diet, which can lead not only to obesity but also to the development of noncommunicable diseases. More research is also needed to study the effects of the degree of processing of food items and not just their nutrient caloric content.
To sum up: we found a connection between fast food consumption and rising BMI. But we don't actually fully get why it's happening. We need more research. (And good luck to anyone bothering to pursue it when it’s way easier to just continue to beat the ever-popular personal responsibility drum.)
 
Unfortunately, the Daily Mail coverage provides an extreme example of the way our preferred means of talking about obesity can subvert and confuse the facts. The study’s actual results found that for every unit of increase in fast food transactions, the population-wide BMI in the country in question went up by 0.03. 
 
In an extraordinary leap of staggering doltishness, the Mail translates this to literally mean that every time you eat a Big Mac, your personal BMI goes up by 0.03. Think I’m joking? I wish I were:
Research has revealed that a person’s BMI – body mass index – increases by 0.03 every time they eat fast food.
 
The research, published in the Bulletin of the World Health Organisation, also revealed that between 1999 and 2008 the number of fast food meals eaten each year rose from 27 to 33 per person.
 
During the same time period, the average BMI in the 25 high-income countries studied increased from 25.8 to 26.4.
 
As a result, researchers at the University of California, Davis, worked out that every fast food meal is causing a 0.03 increase in BMI.
It almost seems absurd to even give this reporting the time of day, but I’ll do so anyway. This is totally, completely, gob-smackingly wrong. This study did not assess the singular hamburger-related decisions of unique individuals. This study is not looking at individual consequences of Spicy Chicken Sandwich consumption. It is seeking correlation between a population’s overall BMI and fast food business data collected between 1999 and 2008. It has literally nothing to do with the personal impact of a Filet-o-Fish.
 
There are a few other obvious, but critical points to remember here: populations do not eat fast food uniformly, every citizen at the same rate, so when research says the per capita consumption of fast food meals is 33 a year, that does not mean that everyone eats 33 fast food meals per year, because this number is NOT A REAL PERSON. There are many people who never eat fast food; there are many people who eat fast food on a daily basis. 
 
And even people who eat fast food on a daily basis are not necessarily ever-ballooning larger and larger with every Egg McMuffin and Whopper they consume. Some people get fat on nuggeted chicken, and some don’t. There are always other individual factors involved. (See also this bizarre experiment by an Iowa science teacher who ate nothing but McDonald’s for three months and LOST 37 pounds. To prove a troubling point. About, again, personal responsibility.)
 
The truth -- in the US at least -- is that fast food tends to be consumed more in low-income communities, because it is cheap, quick, accessible, and calorie-dense. Low income communities also tend to have higher BMIs, but it would be a major stretch to argue that this is exclusively a result of fast food consumption, as it is more likely to be influenced by a host of issues affecting poor people, from a lack of resources and time for physical activities, to difficulty procuring quality healthcare.
 
Sometimes, ill people get fat because they are sick, and not sick because they are fat. 
 
The study in question did attempt to adjust for income disparities, but the efficacy of their adjustments is difficult to measure, especially since this was not really a study about how class interacts with BMI. Nor is it a study about how an individual’s fast food consumption affects their individual BMI. It IS a study about how government regulation affects population BMI vis–à–vis the easy and unchecked proliferation of fast food restaurants. No matter how hard the Mail wishes it were something else.
 
Here’s a trickier example of uncritical thinking from NBC’s coverage of this study, while we’re at it:
The team also looked at data from the United Nations Food and Agricultural Organization, and found people ate a little less animal fat — something that should be good for health. On average, intake of animal fats decreased slightly from 212 calories per capita per day in 1999 to 206 in 2008. But people were still overeating — a lot. On average, people ate 3,432 calories per capita per day in 2002 and 3,437 in 2008. But most people only need 2,000 to 2,500 calories a day.
Rather than share the conclusion of the study itself -- which, as quoted above, is that fast food consumption seems to influence overall BMI, but also that more research needs to be done because there are probably many factors involved here -- the NBC coverage goes straight to calories as the culprit. Because everybody knows fat people are fat because they eat too much.
 
As in so many things in life, calories are more complicated than they may seem. The FDA’s 2000-2500 calorie target is based on the Basal Metabolic Rate (BMR) of a person who already has a BMI within the “normal” range. When we talk about that 2000-2500 range, we’re saying that people whose weight is already within the parameters that we’ve (somewhat arbitrarily, and based on 19th century math) decided are “healthy” require this many calories to maintain their weight, move their bodies around every day, and not, y’know, starve. 
 
However, not all bodies burn calories at the same rates. Athletes often need more than the FDA recommendation for calories because they use more energy. Likewise, it is also sometimes true that a larger body may burn more calories doing the same things a smaller body can do with less, simply because it can require more energy to move and biologically support a 250-pound body than a 125-pound one.
 
Taking this calculation at face value is how we arrive at the popular assumption that ALL fat people must necessarily be eating far more food than the “average” person, in order to get and remain fat. However, simple math and thermodynamics ignores the fact that bodies are not uniform food-processing factories, all operating at the exact same capacity, all burning an identical amount of fuel for an identical return of energy.
 
Even setting aside fat politics for the moment, odds are good that you have known at least one person in your personal anecdotal life who could seemingly “eat whatever they want” and not gain weight. Maybe you are one of those people yourself, and folks have long boggled at your ability to scarf down mountainous portions of pizza and donuts without your waistband being the slightest bit troubled by it.
 
Fat people have unique bodies as well. Some are efficient calorie burners, and some are not. Dieting can have an impact too -- as many people who have been on a liquid diet know, spending a length of time subsisting an extremely low calorie starvation-like diet can result in a magical ability to gain weight on as little 1,800 calories per day later on. And let’s not forget the influence of genetics, which even the most conservative twin and adoption studies have found are responsible for between 40% and 60% of weight variance.
 
Coupled with the fact that so many fat people have also spent large portions of their lives repeatedly weight cycling, which may (or may not, the jury is still out on this) have an effect on an individual’s ability to lose weight without resorting to drastic measures, uncritically asserting “most people only need 2,000 to 2,500 calories a day” is an oversimplification of the highest order.
 
Point being, the higher average caloric intake cited by the NBC News coverage is an average, and not necessarily what most people are actually eating. Some people are eating more than the recommended allowance, and some are eating far less. Curiously, the higher calorie numbers the article cites are themselves a powerful argument against the old chestnut of calories in, calories out, because if that were uniformly true, then one would expect our entire population would be gaining weight at a rate that far exceeds the actual growth of obesity. 
 
The truth is that since 1999, obesity rates have been practically flat among children and adolescents, as well as adult women (and only slightly up for adult men) -- so it’s hard to see these higher caloric intake averages as something to get terrifically freaked over.
 
Did you catch that last part? About obesity rates not significantly increasing in the US since 1999? Are you thinking, But wait, everyone knows obesity is skyrocketing out of control, higher and higher all the time, everyone is constantly getting fatter and we need to worry about it a lot! And have you ever asked yourself why we think we know that?
 
We don't question it, or look for evidence any more than we’re likely to track down and read the actual study the Mail’s “every fast food meal = 0.03 increase in BMI” story is erroneously based on. We're happy to believe we just know. We read popular articles that treat public health studies across broad populations as individual mandates.
 
Just like the BMI itself, which was never intended to be used to determine the healthy weight of a single individual.  In 1832, Adolphe Quetelet came up with the math on which our current BMI is based, using data from a few hundred Belgians. The BMI as we know it was was devised in 1972 by Ancel Keys exclusively for use in population studies, and not to diagnose individuals, because it is unreliable for individual diagnosis.
 
And what do we do? We use it to diagnose individuals, every day.
 
The UC Davis study isn’t a bad study, by any means. It's an interesting global look at one factor that may be influencing BMI trends. The problem is in how we popularly understand it, or more precisely, how we choose not to understand it. The role of public health research is not to describe individual processes within a discrete body -- that’s what biology is for -- but rather to assess generalized trends and changes across large populations. It’s not about blame. It’s not about personal responsibility. It’s certainly not about McNuggets. The study itself makes good-faith recommendations for goverment interventions to improve food choices in the interest of a healthy population, but it also acknowledges its shortcomings and the fact that population-wide BMI is not a simple matter with a single cause. 
 
My purpose in raising these questions is not to convert anyone; my purpose is simply to encourage us all to take a hard look at our uncritical acceptance of certain ideas, and maybe to reconsider what we assume to be true. My issue is with the way we currently talk about weight and health -- which is to say we do not really talk about it at all -- and our stubborn cultural refusal to ask questions and glean facts when it is so much easier to only look for the stories that reinforce what we think we already know about obesity. We have no use for details, nuances and reality when we can rely on the reassuring comfort of unquestioned conventional wisdom.