Reporter: Helen Wellings

Supermarkets -- we spend on average about 3 to 4 hours a week scouring their shelves and prowling up and down their aisles. But, the shelves harbour big secrets and shoppers are getting caught out. Tonight, we reveal those secrets -- the top four Supermarket myths that spell danger to you, your health and your wallet -- and what better myth buster than Ria Voorhaar from Consumer watchdog, CHOICE..

Supermarket Myth No.1 -- so-called "Fresh" Vegies are Best.

"Fresh vegies aren't always best. What CHOICE found is that vegetables start to lose their nutrients as soon as their picked", Ria said.If you're not eating fresh vegetables straight away, but storing them for days in the fridge, you would be better off serving canned or frozen varieties. And just how old and how far have they travelled before you buy them? "With fresh vegetables they can be picked and sit in a warehouse for a while and go across the country. Technological advances mean they look better for longer, then once you take them home. they sit in the fridge for a couple of days -- that entire time the nutritional value of that product is decreasing", Ria said.

And Frozen versus fresh .. CHOICE's investigation found frozen vegetables are generally more nutritious than the supermarket's fresh, except for broccoli where fresh has more vitamins and minerals than frozen broccoli. Once cooked, frozen green beans have twice as much Vitamin C as fresh beans.

Cooked, frozen English Spinach is more nutritious than the supermarket's fresh spinach. Carrots -- their Vitamin C levels were about the same whether fresh, frozen or canned. Corn, there was also little difference in the Vitamin C levels found in frozen and canned compared with the supermarket's fresh corn off the cob. "CHOICE recommends you start shopping in places like farmers markets and green grocers where you know where the produce has come from", Ria said.

Supermarket Myth No.2 -- Bigger is Better.

"A recent CHOICE Investigation found that while most people would think buying in bulk would save them money, that's not always the case. For example a Pedigree dog food - -a smaller tin actually worked out better value than a larger one", Ria said.

A Choice Investigation found the 1.2kg tin of Pedigree dog food was 22% more expensive per 100grams than the smaller 700 gram tin of the same product. "Retailers are only displaying the full price which means you basically have to have a degree in maths to work out which is the better value product for you", Ria said.

Which is why Choice is calling for the introduction of unit pricing in Aussie supermarkets, forcing supermarkets to display the price per 100 grams or per litre for all products. "So if the price was displayed per 100 grams or per hundred mls, it would be much easier for someone to work out what that product costs compared to something similar", Ria said.

The bigger 825 gram Kellogs Cornflakes packet only represented a 2% saving over the smaller packet. "What we call Supermarket Truth in pricing is already in the UK, the EU and many US states, where consumers can very easily see what the actual cost of the product is and compare it with other products that are available", Ria said.

Supermarket Myth No.3 -- Diet Cola is a Healthy Choice.

"Diet Cola is not a healthy choice. People often look to diet cola as a way to limit their sugar intake but what we've found in an investigation is that Diet Cola contains artificial sweeteners and regular consumption of artificial sweeteners actually enhancers your appetite for sweet things and indirectly lead to you putting on weight", Ria said.

And a warning to mum's and dads. Your kids are at risk of consuming too much artificial sweeteners found in diet soft drinks. "These sweeteners in the past have been linked to health problems such as cancer - what were saying is you should limit your intake of artificially sweetended food and drinks just as you would food and drinks", Ria said.

Supermarket Myth Number 4 -- Light food means weight loss.

"Look at the label and see what the energy is. It might be low fat but you're not going to get thin on it", Ria said.

The author of CSIRO's Wellbeing Diet, Dr Peter Clifton warns that both adults and children can be tricked into having far too much of what seems to be a good thing. "They might be a little bit deceived, they think buying low fat, low energy and some of the time its not true. The energy is the same, so it's not a dramatic reduction in energy as fat", Ria said.

Dietician, Tanya Ferretto says many of her clients have bought into this myth and packed on the kilo's as a result. "Look at the chart, just don't buy because of the claim on front because that can be misleading", she said.

The trick is while the bad fats may be reduced, food manufacturers load more sugar in for flavor and in many cases the calorie or kilojoule count isn't that different to the regular product.