Gay men are also less likely to be overweight than their straight counterparts and are instead more at risk of being underweight, said researchers at UCL and the University of East Anglia.
The study, published in the Journal of Public Health, is thought to be the first to investigate the relationship between sexual orientation and body mass index (BMI) using population data in the UK.
Researchers say the findings support the view that sexual identity should be deemed a “social determinant of health”.
Lead researcher Dr Joanna Semlyen said there were a number of possible explanations for the study’s findings.
She said: “We know that sexual minority groups are more likely to be exposed to psychosocial 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.
“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.”
The academic, from the University of East Anglia’s Norwich Medical School, added: “We found that women who identify as lesbian or bisexual are at an increased risk of being overweight or obese, compared to heterosexual women”.
She said this was “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,” Dr Semlyen said. “We also found that gay men are significantly less likely than straight men to be overweight or obese.”
The study showed there is a relationship between sexual identity and BMI and that this link appears to be different for men and women, the researcher said.
She noted sexual orientation was not recorded in health surveys until 2008 – meaning that until recently it has not been possible to determine health inequalities affecting lesbian, gay and bisexual people.
“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,” she said.
For the study, researchers pooled data from 12 UK national health surveys involving 93,429 participants.
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