Where a doctor tips the scale could influence discussions about weight with a patient.

A new Johns Hopkins study found that physicians with a normal BMI were almost twice as likely to discuss weight loss with obese patients than doctors who were overweight themselves. Obese doctors were 86-percent less likely to diagnose obesity if they thought a patient's BMI met or exceeded their own.

The study showed normal-weighted doctors had greater confidence when giving weight loss advice or referring patients to diet and exercise counseling.