While losing weight for health reasons is generally viewed as a positive move, the decision may have an adverse impact on a person's romantic relationship, a new study suggests.

According to US scientists, problems may arise if one half of a couple is not as interested in introducing a healthier lifestyle.

"People need to be aware that weight loss can change a relationship for better or worse, and that communication plays an important role in maintaining a healthy relationship," commented the study's lead author, Dr Lynsey Romo, of North Carolina State University.

As part of the research, 21 couples were surveyed about their relationships. Within each of the couples, one of the people had lost at least 30lbs in less than two years. The average weight loss per person was 60lbs.

Each participant was asked about the impact of the weight loss on their relationship, whether it was them who had lost the weight or their partner.

The scientists found that after the weight loss, communication generally improved within the couples. The person who had lost the weight was more likely to talk about healthy behaviours and this tended to inspire their partner to also become more healthy.

Within couples where both partners were happy to make healthy changes, interactions tended to be more positive and levels of emotional and physical intimacy increased.

However, the scientists also noted a ‘dark side' when it came to weight loss among certain couples. Communication appeared to become more negative, for example, the person who had lost weight would nag their partner to follow suit. This caused a lot of tension.

Meanwhile some people who had not lost any weight said that they felt threatened and insecure by their partner's loss of weight.

These people tended to be resistant to change and would even attempt to sabotage their partner's weight loss efforts by, for example, criticising them, showing less interest in sex and trying to tempt their partner with unhealthy foods.

This, the scientists said, was done in an attempt to prevent their partner and their relationship from changing.

"This study found that one partner's lifestyle change influenced the dynamic of couples' interaction in a variety of positive or negative ways, tipping the scale of romantic relationships in a potentially upward or downward direction.

"When both partners bought into the idea of healthy changes and were supportive of one another, weight loss appeared to bring people closer. When significant others resisted healthy changes and were not supportive of their partner's weight loss, the relationship suffered," Dr Romo explained.

She said that this study should not dissuade anyone from losing weight, but it should ‘encourage people to be aware of the potential pros and cons of weight loss on their relationship'.

"It is really important for the partner of someone trying to lose weight to be supportive of their significant other without feeling threatened by their health changes. This approach will help people lose weight without jeopardising the quality of their relationship," she added.

Details of these findings are published in the journal, Health Communication.