Teenage girls are increasingly looking at fitness bloggers on Instagram and Facebook as role models but it is making them feel guilty that their bodies don't match up, new research shows.

Associate Professor Claire Drummond from Flinders University set out to study what motivates or discourages girls aged 13 to 17 to do physical activity.

But in her interviews with 75 teens she was surprised to find that most of them said their main role models were women who ran 'fitspo' or fitness inspiration pages.

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Rebecca Lomas, from the NSW Central Coast, has 115,000 followers on Instagram and says she is mindful to portray a 'balanced' attitude for her young fans

Ms Lomas, 20, lost 11kg after switching to a 'clean eating' diet, which avoids processed foods, two years ago and has since gathered followers by posting pictures of her workouts and meals

'I thought they would say people like Sally Pearson or their parents, but for the majority it came out that it was these online fitness models on Instagram and Facebook,' she said,

'I asked them to explain what do you like about them and they said the fact they have magnificent, awesome bodies or great abs.

'But they also said things like "Seeing how perfect they are made me feel really bad about my body".'

Professor Drummond said when she looked at the 'fitspo' pages mentioned by her interview subjects, the majority of the women running the sites had no background in fitness or nutrition.

Others were models or personal trainers whose jobs allowed them plenty of time for exercise.

Ms Lomas works for a fitness marketing company and is signed to Chadwick modelling agency

'I try to post every aspect of the health and fitness world, like when it comes to days when I don't feel like working out, because obviously everyone's human and everyone has days like that,' Ms Lomas said

'Some of them have degrees but the majority are doing it because they're, let's face it, genetically-blessed and really good at doing their fitness,' she said.

'A very small percentage can spend all day long working on their bodies, it's just an unrealistic perception that some girls are taking away.'

Associate Professor Claire Drummond from Flinders University

But Professor Drummond said fitness models didn't always have a negative effect.

'They also motivated girls and it's normally the girls who are good at fitness and look at their bodies and think that's something they can do,' she said.

'The girls who are not so active, that's where there are some concerns.'

Rebecca Lomas, 20, from the NSW Central Coast runs the Instagram account @strongisthenewskinny94 and has more than 115,000 followers.

Ms Lomas lost 11kg after switching to a 'clean eating' diet, which avoids processed foods, two years ago and has since gathered followers by posting pictures of her workouts and meals.

Ms Lomas, who works for a fitness marketing company and is signed to Chadwick modelling agency, says she is mindful to portray a balanced attitude.

'I know a lot of young girls are following and they're very impressionable so I do take that into account a lot,' she said.

'I try to post every aspect of the health and fitness world, like when it comes to days when I don't feel like working out, because obviously everyone's human and everyone has days like that.

'Last night I did a post about how bloated I get sometimes.'

She also sells ebooks through her website which contain clean eating tips and recipes.

Ms Lomas, who does not have a fitness or nutrition background, says she tries to stress that her posts are based on personal experience

Ms Lomas, who does not have a fitness or nutrition background, says she tries to stress that her posts are based on personal experience.

'I'm careful when I post things about workouts to say this is what works for me, it might not work for everyone,' she said.

Prof Drummond said she believed fitness models would only grow in popularity so it was important to help teens develop realistic perceptions of health and fitness.

'This is not going to go away, Facebook and Instagram are here to stay,' she said.

'We need to tell our girls to be more critical when they look at these models to understands that this person has great genetics, a lot of time, they can make small meals for themselves and they may not have to worry about brothers, sisters, mums and dads.'