Scooping watermelon cubes and crushed nuts over green tea frozen yoghurt may seem the right way to quash sugar cravings and gain health benefits, but a Choice investigation shows otherwise.

The consumer watchdog's investigation into five frozen yoghurt chains – Yogurberry, WowCow, Mooberry, Yoghurtland and Zwirl – found a potential breach of consumer law and many dubious health claims.

“To distinguish their products from other chilly treats, frozen yoghurt shops often market them as a low-fat, low-kilojoule, high-calcium healthy treat, spruiking their fresh fruit toppings, beneficial cultures, antioxidant-rich goji or acai berries and even omega-3,” said Angela McDougall, food policy adviser at Choice.

Yogurberry, with nine stores scattered around Sydney, claimed its yoghurt contained “vast quantities of bifidus lactobacillus that is not only 'excellent for your digestion' but can also 'aid weight loss and significantly lower the risk of coronary heart disease' ".

Choice has referred this claim and another which read that live yoghurt cultures could “slow the ageing process of the body” to the NSW Food Authority, which has launched an investigation.

“Froyo [frozen yoghurt] might be tasty but it's not a health food and it's unlikely to give consumers the outlandish health benefits claimed by some stores,” Ms McDougall said. “It's important to think of it as a naughty treat like you would ice cream.”

Choice is calling for a nationally consistent kilojoule labelling system for takeaway food, including frozen yoghurt, to help consumers make informed and healthy purchases.

At least 100 brightly lit yoghurt parlours under dozens of new brands such as Moochi, Yogohouse and Twisted have opened in Sydney in the past two years. The craze began in South Korea and shifted to the United States in the past decade.

Choice investigators caught a Yogurberry store, which charges $25 a kilo, rounding up the weight by five grams, adding 12¢ to the price. The National Measurement Institute said this act could be in breach of Australian consumer law since customers must be informed of extra charges.

The Yogurtland chain, which committed to opening 50 stores across Australia, was found charging per fluid ounce, detailing energy content in calories and not clearly displaying the price per kilogram – each act a breach of regulations. Food Standards Australia and New Zealand requires takeaway shops making health claims to provide nutritional information.

Noggi's nutritional calculations were wildly inaccurate, with 100 grams of strawberries being treated as one kilojoule of energy when in reality it is 100 kilojoules.

Frozen yoghurt contained half the calcium content of regular, unsweetened yoghurt and 1.5 times the kilojoule count from the added sugar.

“Many yoghurts and smoothies contain added extras, such as syrups and flavourings,” said Melanie McGrice from the Dietitians Association of Australia. “These products can provide many kilojoules without filling you up – making you more likely to overdo your daily energy [kilojoule] budget.”