Obesity is on everybody's mind it seems. Not a week passes without the release of a study linking obesity to soaring health care costs or a shrill editorial demanding that something be done about America's weight problem. Now, with the help of agencies like the Centers for Disease Control and Prevention (CDC), and the National Institutes of Health (NIH), HBO has joined the panic party with the release of a documentary called The Weight of The Nation.
The documentary is broken into four parts, each dealing with a different aspect of the obesity epidemic. But there are two characteristics running through the entire film: ominous music and pseudoscience. In the next two posts for this column, we'll look at the fallacies discussed in each part of the documentary.
Part 1: Consequences
"Consequences" discusses the scope of the obesity epidemic and the repercussions of being overweight. The message is that Americans are fatter than they used to be, and being overweight carries with it all sorts of devastating medical and social consequences. To make their case, the filmmakers follow several overweight individuals and highlight their struggles with obesity to demonstrate how these problems manifest. Such a presentation is compelling, but what I found equally striking is what wasn't presented during part 1 of the film.
Most obviously absent is any discussion of the problems with the Body Mass Index (BMI), which is the primary method used to assess obesity. Among its many flaws, the BMI arbitrarily draws lines between "normal," "overweight," and "obese" ranges and can't track what a person's weight is composed of. For example, somebody who regularly lifts weights, and thus has more muscle mass, will have a BMI similar to an individual who has a high body fat percentage.
Any measurement that puts two people who are at drastically different fitness levels in the same category can't possibly be very useful. Indeed, multiple studies (references 6,7, and 8) have illustrated that the BMI doesn't accurately predict risk for disease or longevity. More to the point, overweight people often live perfectly healthy lives, and individuals who maintain a supposedly normal weight commonly suffer from conditions regularly attributed to obesity. Recognizing these points is essential to understanding problem, and they are entirely ignored by Weight of the Nation.
The costs of obesity are also touted in part 1. But none of the experts surveyed on the issue mention the costs of caring for healthy people who live longer, which are higher in the long term than health care costs associated with obesity.
Part 2: Choices
"Choices" discusses the science of obesity, what causes the condition and how people can bring down their weight. Weight loss, according to the film, is simply a matter of energy balance. People get fat because they eat too many calories and burn too few through exercise. This is the accepted wisdom in dietary science, but it has never been well supported by the evidence.
No attention is paid during the film to the overfeeding or starvation studies showing that the well known energy balance equation doesn't account for body weight. In one famous study, prison inmates ate upwards of 10,000 calories and most gained no weight. Those who did very easily lost the weight gained during the study. More recent overfeeding studies have found the same.
Similarly, as Gary Taubes discusses in Good Calories, Bad Calories, obese patients put on semi-starvation diets and made to exercise every day often don't lose weight. If they do, they put the weight back on easily despite adherence to their diets and exercise regimens because "... the body naturally compensates" for the changes in energy intake and expenditure. For the eat less, exercise more hypothesis to work, energy intake and expenditure have to be independent of each other, but they are inextricably linked.
So-called fad diets are also blasted by the film's experts. Frustratingly, low carb diets are counted as fad diets, but none of the research indicating that carbohydrates are uniquely fattening because they raise blood sugar and stimulate an insulin response is discussed. Clinical trials showing that people lose weight and reduce their disease risk when they go on low-carb diets are also ignored in Weight of The Nation.
Soda and other sugary drinks are blamed disproportionately for obesity because most of our calories supposedly come from the drinks, but the CDC's own data show that this is not the case. Most of the calories Americans consume come from food, much of them from junk food. It is also odd that the filmmakers interview Dr. Robert Lustig about childhood obesity but don't ask him about the calories in, calories out hypothesis, which he undeniably rejects. Like many experts, Lustig argues that calories are not all equal; the ones that come from sugar are worse than the calories that come from other foods
Of course, the film isn't all bad. It correctly points out that stress can impact weight gain and accurately describes the benefits of exercise, to name two examples. Nonethelss, the film gets many more things wrong. And it is nothing short of annoying to see popular documentaries backed up by prominent doctors and scientists misleading the public about such an important health issue. However well intentioned the filmmakers are, The Weight of Nation isn't going to help solve the obesity problem.