Men are three times more likely than women to struggle in telling their partner they need to lose weight, research has suggested.
Almost a third of men (31%) do not want to confront their partner about shedding pounds, compared with 10% of women who would not be happy to tell their man to slim down.
But women are much more likely to find it difficult to tell a close friend to go on a diet (23%) compared with men (8%).
The poll of more than 2,000 people was commissioned by the International Chair on Cardiometabolic Risk (ICCR) to highlight the risks of being overweight, in particular around the belly.
Abdominal fat around the waist increases the risk of Type 2 diabetes, coronary heart disease and stroke.
The poll, supported by the National Obesity Forum, found 59% of people worried that a loved one with a large waistline would develop serious health problems.
But 31% said the fear of hurting their feelings or provoking a bad reaction would prevent them from telling them they needed to lose weight.
Professor David Haslam, chair of the National Obesity Forum, said: "Suggesting to someone that they should consider losing a few pounds may not be a comfortable conversation to have but if someone close to you has a large waistline, then as long as you do it sensitively, discussing it with them now could help them avoid critical health risks later down the line and could even save their life."
Dr Jean Pierre Despres, scientific director of the ICCR, said: "Earlier this year, ICCR found that 41% of Britons do not realise that having fat around their waistline is worse for their health than fat stored elsewhere on the body.
"This is about health not vanity. Start by encouraging someone close to you to make simple lifestyle changes such as becoming more active, making small alterations to their eating habits and replacing sugary drinks for water."