Individuals vs. Populations: What Can Doctors Do For Obesity?

8/10/2016

by Jason Block, MD, MPH

Several months ago, I got into a twitter spat. In response to a blog post that decried how inadequately doctors were treating patients with obesity, I wrote in a series of tweets: “When will we stop blaming doctors for what they fail to do about obesity and accept that they cannot reverse the epidemic? Primary care docs have a role but not enough support or time to spend on obesity while treating myriad other issues. Reversing obesity is more of a policy and societal challenge than a health care matter. Surgery and drugs can only do so much.” In response, the author of the original blog post wrote another piece, quoting me anonymously, lamenting that I thought there was nothing that doctors could do to treat obesity.

This got me thinking. Was I imprecise in my series of 140 character missives? Did the author misrepresent my comments? Or, was this a misunderstanding about the concept of individuals vs. populations? While some combination of these was likely at play, conflating individuals and populations was a big part of it. It was time to revisit Geoffrey Rose, a famous physician and epidemiologist whose seminal work was The Strategy of Preventive Medicine.

I’m a primary care physician, and I work in a weight management clinic in addition to seeing my primary care patients. I wholeheartedly believe that we should pursue weight loss treatment for patients with obesity and can do so successfully. Diet, medications, and bariatric surgery are all options for patients, and I recommend each of these methods for appropriate patients. But, this isn’t easy. Obesity treatment is a challenge, and most patients cannot sustain weight loss for very long (those who undergo bariatric surgery are an exception). Doctors don’t have much support for treating obesity while also being expected to manage other chronic conditions and preventive care, insurance coverage of obesity treatments has gaps, and treatment can be expensive. Also, patients who lose weight battle against physiological changes that make it difficult for them to sustain that loss. That being said, some patients are successful, and it is our obligation to help patients. We also need to improve access to appropriate treatments, and provide doctors with more support than they currently have.

Geoffrey Rose calls this individually-focused effort to treat disease a “high-risk strategy.” What did he mean by that? Defining “disease” depends on setting a somewhat arbitrary threshold for a measure that underlies that disease (e.g., blood pressure for hypertension, cholesterol for hypercholesterolemia, body weight for obesity). Experts define the threshold, and people above it have the “disease.” This doesn’t mean that people who are just below the threshold won’t experience complications from the condition -- is a systolic blood pressure of 139 really better than 140? But under a “high-risk strategy,” we focus most of our efforts on those people with the disease. This is how medicine works and what doctors do. We treat patients with hypertension, hypercholesterolemia, and hopefully obesity, with a target to get them below the range that defines the disease.

But population trends and remedies to declining population health are a separate construct entirely. While the “high-risk strategy” is efficient in that it helps patients who are most at-risk for developing a bad health outcome, it remains that, as Rose states, “a large number of people at a small risk may give rise to more cases of disease than the small number who are at a high risk.” This is simple math. For example, only 1/3 of the US population has the disease of obesity. Yet, while the risk of weight-related consequences is lower in those who do not have obesity, the sheer size of this group leads to more cases of weight-related consequences than are found in the group with obesity.

Let’s construct a hypothetical to show how this works. In a fictional population of 1 million, let’s say:

· 10% of patients with obesity will have a heart attack in 10 years, and that 300,000 (30%) people have obesity. Well, 30,000 people with obesity will have a heart attack.

· Patients without obesity have a 5% risk of a heart attack in 10 years, and that 700,000 (70%) people don’t have obesity. Well, 35,000 people without obesity will have a heart attack.

There are more heart attacks in the lower risk group!

For a disease less common than obesity, the differences would be even greater. Here is Rose again: ““A large number of people exposed to a small risk may generate many more cases than a small number exposed to a high risk.”

Thus, if we want to prevent the most heart attacks, we should focus our efforts at the population level on the largest group, in this case the people without obesity. We also can try to prevent this large group without obesity from gaining weight and thus later falling into the high-risk group. This might involve population-wide measures like large-scale public education, reducing calories in restaurant food, supporting the provision of fruits and vegetables in schools and nutrition assistance programs, and discouraging unhealthy foods in those settings. Of course, this “population strategy” has its drawbacks, primarily because, as Rose states, “a preventive measure which brings much benefit to the population offers little to each participating individual.” Not to mention cries of a nanny state and big brother.

This doesn’t preclude treating individuals with obesity. We should. Doing so will help some patients . We just can’t expect that it will reverse the epidemic. If we want to do that, our approach should start with Rose, and we need to understand the differences between individuals and populations.

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