For the study, published in the journal PLOS One, the researchers from the University College London and Anglia Ruskin University in the UK, picked nearly 5,000 sexually active British people.
"I believe the observed association is owing to spouses in satisfying relationships relaxing their efforts to maintain their weight because they are no longer motivated to attract a mate," study lead researcher Lee Smith, was quoted as saying by thesun.co.uk.
"Therefore, those who are overweight are more likely to be in a happy and satisfying relationship and more likely to engage in frequent sexual activity," Smith added.
According to the study, among sexually active older people, fat males were a third more likely than their slim counterparts to have sex in previous week.
The research found that likelihood of having sex in the past year was the same across all sizes. However, fat men did it more often as they have an excess of confidence to go with the flab, said the report.
The researchers also revealed that overweight women were 16 per cent likelier to have had sex in the previous week.
"Some women feel attracted to all that protective bulk. Well-fed men also have an excess of energy to burn," psychotherapist Phillip Hodson, was quoted as saying by thesun.co.uk.
( With inputs from IANS )