Children with separated parents may also spend more time alone at home, giving them increased access to junk food and perhaps less chance to exercise.
They added it might also be that single parents have less time to prepare home-cooked meals and instead have to reach for prepackaged dinners or fast foods.
In the new study, the Norwegian researchers also discovered that children who eat breakfast and dinner with their parents are less likely to be overweight than those who don't.
The researchers studied 8,000 children from eight European countries and found children who ate breakfast with their parents five to seven times a week were 40 per cent less likely to be overweight than those who had breakfast with their parents two to four times or less each week.
Those who also had dinner with their parents five to seven times a week were 30 per cent less likely to be overweight than those who shared less evening meals at home.
Lunch was different, the data showed, with children who regularly had lunch with their parents 20 per cent more likely to be obese.
Further research presented at the European Congress on Obesity revealed that eating just three slices of white bread a day raises a person's chances of becoming overweight or obese by almost 50 per cent.
The researchers, from the University of Navarra in Spain, tracked the weight of almost 10,000 people for five years.
They found that those who ate 120g or more of white bread a day were 40 per cent more likely to pile on the pounds than those who ate 60g a week or less.
The weight gain seen couldn't be explained by the white bread lovers having a less healthy diet in general.
Instead, it is thought that lack of satiety-inducing fibre and the high sugar content in it takes its toll on the waistline.
Professor Jason Halford, chairman of the UK Association for the Study of Obesity, said: "I would say white bread is a concern because it is generally lower in useful nutrients such as fibre and it can contain added sugar and sometimes contains higher levels of salt."
- Daily Mail