From romantic dinners to nights in on the sofa watching TV, munching on snacks - it's no wonder couples pile on the pounds.

Now scientists have confirmed being in a settled relationship really does increase the likelihood of weight gain and explained why.

Australian researchers made the conclusion after assessing 10 years worth of data from 15,000 participants.

The Central Queensland University study showed couples weigh more than single people - despite having healthier lifestyles and eating more fruit and vegetables.

Stephanie Schoeppe, lead author, told NewScientist that it could be down to them no longer needing to impress potential suitors.

And she warned that children can only add worsen weight problems, as parents tend to munch on their 'leftovers and snacks'.

Australian scientists have today confirmed the theory that you pile on the pounds when you settle down in love

She said: 'When couples don’t need to look attractive and slim to attract a partner, they may feel more comfortable in eating more, or eating more foods high in fat and sugar.

'When couples have children in the household, they tend to eat the children’s leftovers or snacks.'

Couples have for decades moaned about their battle with the bulge after falling in love.

Cosy evenings spent binge-watching TV and munching popcorn on the sofa have taken the brunt of the blame.

But the new study, published in the medical journal PLoS ONE, suggests the weight gain isn't from an unhealthy lifestyle.

HOW TO CALCULATE YOUR BODY MASS INDEX - AND WHAT IT MEANS Body mass index (BMI) is a measure of body fat based on your weight in relation to your height. Standard Formula: BMI = (weight in pounds / (height in inches x height in inches)) x 703 Metric Formula: BMI = (weight in kilograms / (height in meters x height in meters)) Measurements: Under 18.5: Underweight

Underweight 18.5 - 24.9: Healthy

Healthy 25 - 29.9: Overweight

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It showed that couples consumed more fruit and vegetables and steered clear of fast food, alcohol and cigarettes.

However, experts believe the reason behind comfort weight could be that 'couples are eating more of all food types together'.

Dr Jerica Berge, from the University of Minnesota, commented how so-called date nights and romantic dinners out are responsible.

She told NewScientist the findings 'may be because social behaviour in marriage commonly revolves around eating occassions'.

Volunteers were quizzed about their lifestyle, such as how much fast food they ate and how much time they watched TV.

An analysis of the answers then showed couples and singletons complete the same amount of exercise and sedentary behaviour, on average.

Dr Berge explained this could stem down to couples wanting to live healthier lives to extend the span of their relationship.

Dr Anja Heilmann, from University College London, said: 'How long you’ve been in the relationship for probably matters.'