Lesbian and bisexual women are more likely to be overweight than straight women, a new study suggests.

Researchers from the University of East Anglia have looked at the relationship between sexual orientation and body mass index (BMI) in the UK.

Interestingly, they found that while lesbian women are more likely to be overweight, the reverse is true for men - gay men are less likely to be overweight than straight men.

Based on the findings, the researchers say sexual identity should be considered as a "social determinant of health".

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Lead researcher Dr Joanna Semlyen, from the University of East Anglia's Norwich Medical School, said: "We found that women who identify as lesbian or bisexual are at an increased risk of being overweight or obese, compared to heterosexual women.

"This is worrying because being overweight and obese are known risk factors for a number of conditions including coronary heart disease, stroke, cancer and early death.

"Conversely, gay and bisexual men are more likely than heterosexual men to be underweight, and there is growing evidence that being underweight is linked to a range of health problems too, including excess deaths.

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"We also found that gay men are significantly less likely than straight men to be overweight or obese.

"This study demonstrates that there is a relationship between sexual identity and BMI and that this link appears to be different for men and women."

She said there are several possible explanations for the findings.

"We know that sexual minority groups are more likely to be exposed to psycho-social stressors, which impacts on their mental health and their health behaviours such as smoking and alcohol use, and which may influence their health behaviours such as diet or physical activity," she said.

"These stressors include homophobia and heterosexism, negative experiences that are experienced by the lesbian, bisexual and gay population as a result of their sexual orientation identity and are known to be linked to health."

She added that until 2008, sexual orientation was not recorded in health surveys and until recently it was not possible to determine health inequalities affecting lesbian, gay and bisexual people.

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"We hope that policymakers and clinicians will be able to use this fresh evidence to provide better healthcare and tailored advice and interventions for lesbian, gay and bisexual people," said Dr Semlyen.

Researchers from the University of East Anglia and UCL pooled data from 12 UK national health surveys involving 93,429 participants for the study.