If you want to know whether you’ll lose weight or not, don’t ask a doctor.

In a new study, physicians predicted about 55 percent of patients would be “likely” or “very likely” to follow their recommendations for losing weight, eating healthier or getting more exercise. But three months later, only 28 percent of patients had lost at least two pounds, 34 percent were eating less fat and more fiber, and 6 percent were getting in one more hour of brisk walking each week.

It was surprising, researchers said, that in slightly more than half of cases, doctors said they believed their patients would follow their recommendations, because other work has not shown that physicians have that level of optimism about their patients’ behaviors.

Why the optimism? While physicians generally think patients are unlikely to follow recommendations, after talking with any given patient, doctors become optimistic that the patient will change, the study researchers say.

The findings were published Feb. 7 in the journal Family Practice.

Recordings of doctor’s appointments

More than 60 percent of Americans are overweight or obese, according to the Centers for Disease Control and Prevention.

In the study, the researchers made audio recordings of conversations between 40 doctors and 461 of their overweight or obese patients. The doctors and patients knew their conversations were being recorded, but were told only that the study they were participating in would look at how doctors “addressed disease prevention” with their patients — not that weight loss goals would be looked at, specifically.

After each visit, physicians were asked questions such as: How likely will the patient follow your weight loss recommendations?

When considering the patients who the doctors said would likely improve, most of the time, the docs got it wrong. Only 16 percent of those predicted to lose weight actually lost weight over the next three months. Of those that the doctors predicted would follow their healthy eating recommendations, only 19 percent actually improved their eating habits. Four percent of those predicted to get more exercise actually started doing so.

The physicians were more often accurate in their guesses about who not improve.

While previous studies had surveyed physicians about their expectations for their patients in general, none had asked doctors what they thought about specific patients immediately after an office visit, according to the study.

Is optimism good?

Doctors’ expectations about their patients ability to change is important, because a doctor with low expectations “can lead to patients being less likely to improve their behaviors,” the researchers said. When patients don’t improve behaviors, doctors’ expectations only sink even lower, and a vicious cycle ensues.

But physician optimism might have some benefits. “Patients might feel more confident that they can lose weight when they feel their physician believes they will change,” the researchers wrote. However, this optimism might mean that the doctors are overestimating the effect their recommendations will actually have on patients, and could make doctors less receptive to learning effecting techniques for counseling patients, according to the study.

Follow MyHealthNewsDaily on Twitter @MyHealth_MHND. Find us on Facebook.