Women tend to put on weight and eat more unhealthily when they move in with a boyfriend, a study suggests.
The study found women adopted their partner's eating habits
But Newcastle University dieticians said, in a review of seven studies, that men seemed to become more healthy after they began co-habiting.
The study in Complete Nutrition suggested women's diets tended to increase in fat and sugar after they began living with a partner.
The team said diets change because each partner tries to please the other.
They looked at a range of studies focusing on the eating and lifestyle habits of thousands of subjects who were either married or who co-habited and found the same theme.
Men found themselves eating lighter, healthier meals and more fruit and vegetables, while women moved towards the creamier, heavier dishes like curries and rich pasta meals favoured by their partners.
One study of 20 US couples found men started to eat less meat, while women began eating more.
Another study of 9,043 adults in the US found marriage itself led to women putting on weight, and moving out of marriage was linked to weight loss in women.
The authors suggested this was caused by more structured eating and less time for exercise within marriage.
A survey of 3,000 Australians suggested men appeared to prefer a higher fat, higher sugar pattern, whereas females leaned towards healthier food choices.
Study author Amelia Lake, who also carried out her own research on changes in diet of 198 subjects between the ages of 11 and 30, said: "A significant proportion of women said they see their partner's influence on diet as negative - whereas men viewed their partner's influence as positive."
"You've got two separate food systems coming together and no matter what people say you are not going to like all the same foods.
"If one partner is always saying 'take away, take away' and the other is always saying 'salad, salad', it could cause problems and there will obviously need to be some compromise."
But Dr Lake also said that couples should see the lifestyle change as a chance to improve both partners' lifestyles for the better.
"It's a time in your life when lots of things are changing and you can work together and do it more helpfully.
"That's the overwhelming take-home message of our review," she added.
Dr Frankie Phillips of the British Dietetic Association said the study indicated that the eating boundaries change for both partners, with the women losing out as they bring their man more in line with their healthier eating principles.
She said: "If women are finding themselves struggling with weight after moving in together, portion sizes would be one of the first things to address.
"On average men require more energy (calories) per day than women, and so having equal portion sizes could mean that women are eating too much."
She added: "Eating together should be one of the simple pleasures in life, and should not be a battle of wills between partners who have different eating philosophies and preferences.
"As with everything in a good relationship, the best way is to reach a compromise where both partners stand to make a gain in improving their health."