60 to 80 percent of people surveyed have not been forthcoming with their doctors about information that could be relevant to their health, according to a new study. Besides fibbing about diet and exercise, more than a third of respondents didn’t speak up when they disagreed with their doctor’s recommendation. Another common scenario was failing to admit they didn’t understand their clinician’s instructions.

When respondents explained why they weren’t transparent, most said that they wanted to avoid being judged, and didn’t want to be lectured about how bad certain behaviors were. More than half were simply too embarrassed, to tell the truth.

“Most people want their doctor to think highly of them,” says the study’s senior author Angela Fagerlin.

“They’re worried about being pigeonholed as someone who doesn’t make good decisions,” she adds.

The trouble with a patient’s dishonesty is that doctors can’t offer accurate medical advice when they don’t have all the facts.