Lesbian and bisexual women are at increased risk of being overweight or obese compared to heterosexual women, according to new research from the University of East Anglia and UCL.
Gay men however are less likely to be overweight than their straight counterparts, and more at risk of being underweight.
The study, published today in the Journal of Public Health, is the first to investigate the relationship between sexual orientation and body mass index (BMI) using population data in the UK.
The findings support the argument that sexual identity should be considered as a social determinant of health.
The research team pooled data from 12 UK national health surveys involving 93,429 participants and studied the relationship between sexual orientation and BMI.
Lead researcher Dr Joanna Semlyen, from UEA'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.
"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.
"There are a number of possible explanations for these findings. 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.
"Until 2008, sexual orientation wasn't recorded in health surveys. This means that until recently it has not been possible to determine health inequalities affecting lesbian, gay and bisexual people.
"Continued collection of data on sexual orientation identity within national health surveys allows us to measure the health of sexual minorities.
"We hope that policy makers 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. We need longitudinal research to understand the factors underlying the relationship between sexual orientation and BMI, and research to understand more about being underweight, especially in this population."