According to the Hungry Jack's website, both the cheese and the ''veggie patty'' used on the burger contain rennet - an enzyme derived from the stomach lining of cows.

But a Hungry Jack's spokesman told the Sunday Canberra Times the company had never claimed the Veggie Burger was a suitable alternative for vegetarians.

''Hungry Jack's has intentionally never marketed its Veggie Burger as vegetarian due to the many different interpretations of what constitutes a vegetarian diet,'' he said.

''While the vegetable patty is cooked in canola-based oil, it does contain cheese which is traditionally and most commonly produced with the aid of animal rennet.''

Choice spokesman Christopher Zinn said most Australians would make the natural assumption that a ''veggie'' burger was vegetarian.

''It seems fair enough to me that a 'veggie burger' should be vegetarian,'' he said. ''While we applaud the disclosure, it certainly raises questions about what else the burgers contain if the Veggie Burger at Hungry Jack's is a Beef Classic.''

Mr Zinn said many people would be shocked to discover they had eaten the burgers under the impression they were vegetarian.

''If I'd walked into a Hungry Jack's six months ago and asked if the Veggie Burger was vegetarian I doubt I would have been told it wasn't,'' he said.

The revelation comes at the same time the fast-food giant announced vegetable cups containing hand-cut broccoli, carrot, celery and capsicum sticks would be introduced as a healthy substitute for fries.

Chief executive Aaron McKie says the new product ''can only be described as a nutritional goldmine''.

''It is a healthy snack of necessary nutrients without unwanted kilojoules and creates a whole new product category for fast food,'' he said. ''We have been quietly improving the nutritional profile of Hungry Jack's products, with major reductions in saturated fat, sodium and sugar levels achieved at a significant cost to the company.''

Mr McKie said kilojoule counts were also added to menus at outlets last week, with most other brands following suit.

But Choice named Hungry Jack's Ultimate Double Whopper as the unhealthiest single menu option and its Angry Angus burger the second most unhealthy menu option.