GPs should stop worrying about causing offence and offer their obese patients help to control their weight, experts have said.
Even if overweight or obese patients go to see their family doctor on a matter unrelated to their weight, GPs should offer them places on a weight loss programme, they said.
The comments come after a new study found that if GPs actively sought to engage their patients about their weight, there could be some beneficial results.
The research, led by experts at the University of Oxford, saw 137 medics challenge almost 1,900 patients about their weight during routine consultations unrelated to weight loss.
At the end of the appointment, patients were randomly given one of two 30-second interventions.
Half were offered a 12-week weight management programme free on the NHS. The other half were advised by their GP that losing weight would benefit their health.
All of the participants were weighed at the first consultation, then at three months they were asked whether they had taken any action to manage their weight, then weighed again at 12 months.
Three quarters of those invited on the weight loss programme agreed to go and 40% attended, according to the study published in The Lancet.
People who were referred to the programme lost an average of 2.4kg compared with 1kg in the control group.
A quarter of participants in the referral group had lost at least 5% of their body weight after a year, and 12% had lost at least 10% of their body fat - double the rate of the control group.
Four fifths of participants (81%) across both groups found the GP's intervention "appropriate and helpful".
Just 0.2% found it "inappropriate and unhelpful".
"Doctors can be concerned about offending their patients by discussing their weight, but evidence from this trial shows that they should be much less worried," said lead author professor Paul Aveyard, lead author, who is a practising GP.
"Our study found that a brief, 30-second conversation, followed by help booking the first appointment on to a community weight loss programme, leads to weight loss and is welcomed by patients
"On average, people consult their doctor five times a year, meaning there is huge opportunity to deliver this low-cost intervention on a large scale."
Rachel Clark, health promotion manager at the World Cancer Research Fund, said: "This study raises some interesting and urgent points.
"We live in a society where being overweight or obese is becoming the norm, but this needs to change as people are putting themselves at risk of developing a number of serious health conditions including 11 common cancers.
"Health professionals play a key role in helping people make healthy lifestyle choices, but it can be difficult to start a conversation with a patient about their weight.
"Unfortunately, we know many health professionals don't feel equipped to support patients with their weight.
"Tackling overweight and obesity must become a health priority within the NHS."
Dr Alison Tedstone, chief nutritionist at Public Health England, said: "It's important that GPs talk to their overweight and obese patients about losing weight and help them to find further support, as many do already. An extra 30 seconds could make all the difference; it doesn't take long and can be raised in a supportive and sensitive manner."