Would you take weight-loss advice from a doctor who hasn't got control of his own size?

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Related Heavier Docs Less Likely to Tackle Patient Weight MedPage Today

It inspires confidence when a dentist has good teeth, or a hairstylist has a chic ‘do, or when the salesperson at a boutique has an immaculate sense of personal style. The same may be true of doctors who maintain a healthy weight — which may help explain why those who are overweight are less likely to broach the topic of weight loss with their patients.

In a study of 500 primary care physicians around the country, researchers at the Johns Hopkins Bloomberg School of Public Health and the Johns Hopkins University School of Medicine found that a doctor’s own size influenced how he or she cared for patients with weight problems. Overweight or obese physicians were less likely to discuss weight loss with heavy patients: only 18% of these doctors discussed losing weight with their patients while 30% of normal weight physicians did.

What’s more, the researchers found that 93% of doctors diagnosed obesity in their patients only if they believed their own weight was equal to or less than that of their patients; only 7% of doctors who believed their weight exceeded that of their patients diagnosed obesity.

“I was totally surprised by the findings,” says lead author Sara Bleich, an assistant professor of health policy at Johns Hopkins Bloomberg School of Public Health.

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The study builds on earlier work that analyzed how doctors’ own smoking habits affected their advice to patients; there, too, researchers found that physicians who lit up were less likely to recommend smoking cessation for their smoking patients, most likely because of the hypocritical nature of their telling patients to quit while they continued to puff away themselves.

But the results also shed light on the complexities of the doctor-patient relationship, especially concerning obesity, and suggest that anti-obesity efforts that focus nearly exclusively on patients may be too one-sided. Indeed, doctors are just as heavy as the rest of Americans: the Johns Hopkins study found that 53% of the physicians were overweight or obese, which tracks with the 64% of U.S. adults who fall in the same categories.

That means that doctors’ weight may be playing an indirect role in perpetuating the obesity epidemic on several levels. First, by not addressing healthy weight with their patients, these physicians are passing up an opportunity to help people improve their health and avoid chronic weight-related conditions such as heart disease, diabetes, hypertension and joint disorders. Second, overweight doctors are putting their own health at risk. And third, they may be sending the wrong message about weight to their patients, who might rationalize their own prodigious size if their doctors look the same as they do.

“For me, the results raise a lot of questions,” says Bleich. “I’d be surprised if this behavior is intentional. I think a lot of it is subconscious. What this study suggests is that physical attributes of physicians have a much bigger contribution to their care of patients than I realized before.”

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In the study, when overweight or obese doctors did address obesity, they were more likely than their normal weight counterparts to prescribe anti-obesity medications (26% vs. 18%), rather than lifestyle changes such as diet and exercise. That may reflect a lack of confidence in these approaches to weight loss, either because of the physicians’ own personal experiences or because of their subconscious concern that such advice wouldn’t appear reliable to patients coming from someone who wasn’t slim.

Most experts say that changes in diet and exercise habits are a crucial part of any long-term weight-loss strategy, even if patients use medications initially to kick-start weight loss.

Compared with overweight doctors, slim physicians were more confident in their ability to dispense advice about diet and exercise to heavier patients, and 72% believed that they should be models of healthy weight for their patients. Only 56% of heavy doctors said the same.

The results represent yet another challenge in the war against obesity — doctors are notoriously bad at taking care of themselves and at being good patients — but the study also signals an opportunity. “If we improve physician well-being, and improve their lifestyles toward weight loss or weight maintenance, that can go a long way toward influencing the care they provide their patients,” says Bleich.

Doctors who have successfully lost weight and who eat well and exercise regularly may be more likely to share their own experiences with patients, making it more likely that their patients will in turn follow their advice, Bleich says. “By making physicians healthier, we are making patients healthier, and helping two groups at one time,” she says.

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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.