Yes, indeed - this is what the National Obesity Forum is recommending. Cited in the BBC news. And apparently it's important to say 'fat' and not 'obese', because that will motivate people more! It is recommended that men are no larger than 94cm (37in) and women 80cm (31.5in) around the waist.
Christmas may be a time of indulging for many, but health experts believe it is the perfect time to tell a loved one they are overweight.
The National Obesity Forum and International Chair on Cardiometabolic Risk said it was important to be upfront because of the health risks.
Being overweight - particularly around the waist - increases the risk of diabetes, heart disease and stroke.
But a poll by the groups suggests too many people shy away from the issue.
The survey of more than 2,000 people found 42% of 18 to 24-year-olds would not tell a loved one they should lose weight because of a fear they would hurt the other person's feelings.
For those aged 25 to 44 it was just over a third, while for older people it was about one in four.
Men find it hardest to tell their partners, while women were more worried about bringing up the issue with a friend.
But with families and friends getting together up and down the country over the festive period, the experts believe there is an opportunity that should not be missed.
Prof 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 International Chair on Cardiometabolic Risk, agreed.
"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 with water."