Men are three times more likely than women to struggle with telling their partner they need to lose weight, research suggests.
Almost a third of men (31pc) do not want to confront their partner about shedding pounds, compared with 10pc 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 (23pc) compared with men (8pc).
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 two diabetes, coronary heart disease and stroke.
The poll, supported by the National Obesity Forum, found 59pc of people worried that a loved one with a large waistline would develop serious health problems.
But 31pc said the fear of hurting their feelings or provoking a bad reaction would prevent them from telling them they needed to lose weight.
Dr Jean Pierre Despres, scientific director of the ICCR, said: "People need to realise that having excess fat around the waistline, and vital organs such as the liver and heart, can lead to dangerous health conditions.
"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."
The ICCR says men with a waistline greater than 94cm (37in) and women with one greater than 80cm (31.5in) should take steps to lose weight.