Jan. 31, 2012 -- Doctors who are normal weight are more likely to give patients advice on diet and exercise, according to a new study.

And normal-weight doctors were also more apt to make a diagnosis of obesity, compared to overweight or obese doctors.

“Your doctor is often not going to diagnose obesity or have weight loss discussions with you if they weigh more than you do,” says researcher Sara Bleich, PhD. She is an assistant professor with the Johns Hopkins Bloomberg School’s department of health policy and management in Baltimore, Md.

The new survey of 500 primary care doctors shows that doctors who have a normal body mass index (BMI) were more likely to engage their obese patients in weight loss discussions, as compared to overweight and obese physicians, 30% vs. 18%, respectively. Doctors were also much more likely to diagnose someone as being obese if they thought a person’s BMI was equal to or exceeded their own.

Thinner doctors were not only more likely to bring these topics up; they also thought their patients would be more likely to follow their advice. Doctors with a self-reported BMI of less than 25 were considered normal weight. Those with a BMI at or above 25 were considered overweight. The findings appear in the January issue of Obesity.

Exactly why heavier doctors may be less likely to discuss weight loss and obesity is not fully understood.

It’s possible that a heavyset doctor is reluctant to suggest moving more and eating less when he or she knows it didn’t work for them. “They may not want to give advice that is not effective in their own minds,” Bleich says.

Overweight or obese doctors are more likely to recommend weight loss pills, she says. The study did not look at how often the doctors discussed weight loss surgery with obese patients.