From humble beginnings in a handful of locations less than five years ago, the "froyo" experiment has blossomed, partly on the back of a perception that it's a healthy alternative to ice-cream.

But dietitians and nutritionists aren't convinced – there's nothing wrong with the base product, they say, it's the toppings and serving sizes that are the problem, particularly in self-serve stores.

Yet this isn't deterring the punters. More than a dozen different companies now operate close to 50 stores in Sydney alone, almost half of these opening in the past 12 months.

Frozen yoghurt stores can be self-serve or over-the-counter and offer a variety of toppings with a serve of frozen yoghurt. Toppings range from fresh fruit, cereals, nuts and dried berries to different kinds of chocolates, lollies and cookies or flavoured and natural sauces like caramel, honey or fruit puree. Some companies specialise in flavoured yoghurt, with offerings like cereal milk, bubble gum and salted caramel, while others stick to two or three basic flavours.

Multinational company Yogurberry opened its first Australian store at World Square in February last year and has since expanded into 12 other locations.

“Sydney is the biggest frozen yoghurt city in Australia, by a long way,” says Yogurberry head manager Kevin Oh.

"Melbourne and Perth are also popular but Sydney is way ahead of other cities."

Tipped to be one of the biggest food trends of 2013 by global marketing group JWT in their annual "things to watch" list, rapid expansion plans are afoot in Sydney. Yogurberry rival Moochi plan to open another eight stores in Sydney by the end of June while eastern suburbs-based Wowcow expects to launch a dozen stores nationally by the end of the year. Founder Carl Harwin has opened five Sydney stores since launching in Warringah Mall in 2007.

“We've had to educate people about frozen yoghurt for years now,” he says. “It's a great thing for this to be happening. The market's exploding and becoming more educated.”

The massive surge in the popularity of frozen yoghurt is in no small part linked to the success of advertising campaigns spruiking its health benefits. These include being high in calcium and protein; low in kilojoules, fat and sugar (many brands are 98 or 99 per cent fat-free); as well as having active probiotics to aid digestion and the ability to assist with weight loss and lower the risk of coronary heart disease.

“You wouldn't eat it every day but… we hit a very good chord with lots of mums with kids because it is a healthy alternative to ice-cream and kids don't taste much of a difference,” says Cassandra Spies, founder of Twisted Yoghurt, which has stores at Bondi Beach and Bondi Junction.

However, health and nutrition experts warn that while these claims have some truth to them, frozen yoghurt is not automatically a healthier choice.

“It's made out to be this amazing health food but really when you look at it... there's not always a lot of difference between low-fat ice cream, gelato and frozen yoghurt,” says Kellie Bilinski, spokesperson for the Dietitians' Association of Australia.

“As far as being low fat, you can get a lot of ice creams that are lower in fat. Gelato is in most instances fat-free, unless it's made with dairy… They're all high in sugar, and with that comes the calories.”

Clare Collins, professor of nutrition and dietetics at the University of Newcastle, says the way frozen yoghurt is sometimes advertised can “confuse people on the street who don't know about nutrition, making it harder for people to make healthy choices”.

“I walked into [a frozen yoghurt store] and I was horrified at the marketing,” she says. “A lot of them say 98 or 99 per cent fat free but when you look at the array of toppings you can add to your supposedly low-fat yoghurt, there won't be anyone who can make it out of there without bags of lollies and chocolates and all the rest of those things that can basically kill you if you have too much of them.”

A serve of frozen yoghurt without any toppings has less kilojoules than the equivalent serve of full-fat ice-cream, Collins says. But most people will use this as an excuse to pile on sugary, fatty toppings and increase their serving size, she warns.

“They call it the 'halo effect', that 'I'm so good I'm having a low-fat yoghurt but I'm going to murder it with chocolates and lollies and the rest of it',” Collins says. “They claim it's low-GI but I say, 'so what?' It's still the same issue… If you eat twice as much of a low-GI frozen yoghurt as a high-GI ice cream, you will cancel the effect.”

The wisest option, she says, is to buy your frozen yoghurt or reduced fat ice-cream from the supermarket, where the packaging and nutrition information will tell you exactly what you're getting in a serve and you won't be tempted by toppings.

“If you're healthy and active and it's just a treat, then enjoy it in moderation,” Collins says. “But if your New Year's resolution was to drop a dress size or be healthier in 2013, my advice is: don't go in there in the first place.”

Of course, not every person who walks into a frozen yoghurt store is there for the health benefits and many companies maintain that taste is the major drawcard.

"I have customers who come in and sit there at the counter asking all these questions about the fat content and sugar content and the nutritional benefits of yoghurt, then they'll go and pile on the chocolate biscuits and lollies and other toppings, so clearly they can't be that concerned about it," Harwin says.

Either way, it's up to consumers to decide whether they want to be healthy or not, Spies says.

"We offer a choice. We have toppings if you're trying to be good - like chilled fruits and different types of nuts - and toppings if you want to be a little bit naughty."