Of concern, 12 per cent said they would seek advice from social media influencers.
The findings have prompted a call for people to be more savvy about where they source their diet advice.
"While there is some great evidence-based material on the internet, there is a lot of paid content as well," said LiveLighter campaign manager, Alison McAleese.
Ms McAlesse says ads for weight loss products - which people often don't need - can be disguised as health advice or information.
"Have a look at whether there is a cost involved and what do they want you to buy to improve your weight. When it comes with a whole lot of products, you have to question why," said Ms McAleese.
Internet users should also be particularly cautious about highly restrictive, 'quick fix' diets found online and question the credibility of advice spruiked by personalities on social media.
"You don't need any qualification whatsoever to be giving your opinion on social media, so people should really watch out for that and check where people are getting their information from," warned Ms McAleese.
"There's lots of great well-known organisations that use evidence and do have a social media presence, so try and check in with those ones instead," she added.
TOP TIPS FOR WEIGHT LOSS:
* Watch portion size
* Avoid sugary drinks
* Cut back on salt
* Cut back on alcohol
* Watch the fats you eat
* Go for 2 fruit and 5 veg
* Cut back on sugar
* Choose health snacks
* Be active everyday