It's not nice to call someone fat. That's a simple rule of thumb, repeated by parents of small children everywhere. For physicians, however, it's a social nicety that must be set aside if they are to act in the best interests of an overweight or obese patient.

And yet, a study released Monday in the Archives of Internal Medicine finds that one in three patients whose body mass index (BMI) is in the obese category has never heard the "O" word from his or her physician. That failure occurs despite obesity" href="http://www.cancer.gov/cancertopics/factsheet/Risk/obesity" target="_blank">copious research linking a BMI above 30 to higher rates of cardiovascular disease, certain cancers, Type 2 diabetes, musculo-skeletal pain disorders and even depression and dementia.

Among patients whose BMI falls in the "overweight" category, a little over half (55%) said they had never been told by a physician that their weight exceeded normal, healthy standards, the archives study found.

Does it matter whether a doctor has uttered those fateful words: "You need to lose some weight"?

A package of articles in the issue of Archives of Internal Medicine out this week says it does. According to one study conducted by researchers at the Medical University of South Carolina and Imperial College, London, patients who have heard from their doctor that they are overweight or obese are far more likely to recognize that they weight more than they should; they are more likely--eight times as likely for the overweight and five times as likely for the obese--to say they want to lose weight; and they are more than twice as likely to have tried to lose weight in the past year.

That's certainly no assurance that overweight or obese patients will lose enough weight to fall into the normal, healthy range, or that they will succeed in keeping lost weight from returning. (As an accompanying study in the package demonstrates, both are devilishly difficult and, in the case of maintaining weight loss over the long term, successful only about 60% of the time.). But it's a start.

"Early recognition of overweight and obesity and communication to patients about their weight is an important initial step to successful behavior change," writes Dr. Robert B. Baron of UC San Francisco, and director of the UCSF Weight Management Program.

It should be noted that until recently, many physicians declined to tell their patients who still smoked that they should stop, in spite of strong evidence that it matters--a lot--for patients to hear it from them. Even three-minute counseling sessions by physicians can result in quitting rates of 5% to 10%.

We should also acknowledge that doctors routinely say they tell overweight and obese patients all the time they need to lose weight: many just don't hear the message, they say. Studies that ask patients whether their doctor has raised the weight issue don't accurately reflect reality, they add.

Granted that may often be the case. And granted, too, that compared with an earlier study, the latest findings suggest that more overweight patients are now getting the message: a Mayo Clinic study" href="http://www.mayoclinicproceedings.com/content/82/8/927.abstract?ijkey=1792a0c7202d22a1d19eed058247ffb5db2b2d99&keytype2=tf_ipsecsha" target="_blank">2007 study found that only one in five obese patients had been diagnosed as obese or given an obesity management plan.

But, with roughly CDC stats" href="http://www.cdc.gov/obesity/data/index.html" target="_blank">one in three American adults and 17% of American children now classified as obese, why does any doctor hold his or her tongue when examining an overweight or obese patient?

Research tells us it's not just that they're heeding their mothers' advice. Compared with overweight and obese patients themselves, physicians have a more negative view of patients' self-control, their determination to lose weight, and their ability to do so, according to a 2006 study. (That might make them more realistic, but not more encouraging). Time constraints are also frequently cited: as physicians' workloads increase and their time with each patient becomes briefer, many see little value in raising a subject likely to prompt patient push-back--and one for which they have little more than difficult lifestyle changes to offer.

And raising the weight issue is, to be sure, treading into emotionally laden territory. "Some patients may feel insulted," writes Baron, who adds that "using the term 'obese' is not likely to be any better received than the term 'fat.'"

Physicians need to strike a tone of concern rather than judgment about a patient's weight, and to be straightforward in comparing that weight to standard definitions. "Inform patients of their abnormal weight in a manner analogous to telling patients that their blood pressure or blood cholesterol is elevated," he suggests. 

Finally, here's a striking fact from one of the Archives studies published this week: almost 37% of overweight participants in the study and 19% of the obese participants did not consider themselves to be overweight if a physician had not told them they were overweight.

Don't be that guy (or woman): here's the BMI calculator; look it up.