Fast food junkies eager to get their hands on the new KFC Double Down burger will need to walk for around 80 minutes to burn off the burger's 604 calories, a nutritionist says.

The long-awaited bun-less burger will be available at KFC outlets around the country from 10am tomorrow - and if the "Bring the KFC Double Down Burger to New Zealand" Facebook page with its more than 2,000 members is anything to go by there may be a long queue.

However nutritionists have condemned the Double Down's high calorie and fat count.

A single Original Recipe Double Down - which comprises two strips of bacon, cheese and "the Colonel's special sauce" encased in two chicken fillets - has 604 calories, 12.6 grams of carbohydrates, 57.6g of protein and a total of 34.4g of total fat - 11.9g of which is saturated fat.

Comparatively, KFC's Original Recipe Fillet Burger has 513 calories, 45.9 grams of carbohydrates, 32.7g of protein and a total of 20.2g of total fat - only 2.8g of which is saturated fat.

KFC general manager Brent Kitto acknowledged the Double Down is not for everyone, saying it is an "occasional meal".

"Contrary to all the attention and speculation though, the Double Down is actually lower in calories and fat than a number of other burgers already on the market," he said.

"Double Down breaks the mould. With two of everything, there's simply no room for the bun, just the best stuff - chicken, bacon, cheese and the Colonel's special sauce,"

According to the McDonald's website, their McChicken has 366 calories, 34.3g carbohydrates, 16.6g protein and 17.1g of fat, 3.2 of which is saturated fat. Burger King's website does not include the calorie or carbohydrate count for the BK Chicken, however the burger has 38g of total fat.

Healthy Food Guide nutritionist Claire Turnbull said it would take 80 minutes of "brisk walking" to burn off the calories from the Double Down.

"The first thing to say is that they're one of the highest calorie items on their menu ... and one of the highest fat items in a single serving," she said. "What you also have to remember is at KFC people are not going to just eat this on its own. They might order it with fries and a drink.

"In terms of the calories, it's more than we would recommend for most people for a meal. It's certainly higher in fat than we would recommend for most people in meals. For the average person sticking basically 10 to up to 15 grams of healthy fat per meal we would be looking for, that really is a huge whack of fat in one serving, and obviously part of that fat is the unhealthy fat."

While the calories in the burger are only slightly higher than the average meal, Ms Turnbull said people need to worry about the total amount and the types of food they are eating and the frequency they are eating.

"There are no vegetables in there, there's no healthy fat in there, there is no ... whole grain carbohydrate foods are not as evil as everyone makes them out to be - there are none of those in there, it's low in vitamins and minerals ... it is basically not providing the nutrition that somebody needs to keep them going at lunch time or for a snack."

"The reality is society has become normalised to this kind of food and people are consuming it more frequently than they need it.

"[The Double Down] is not what our body needs, it is not what will get the best out of you and your body, so understand this is not healthy food at all."

Ms Turnbull said while KFC might call it an "occasional meal" many people will indulge in the Double Down more frequently than they should.

"I'm all about people having personal choice. In this country some fast food outlets have made some responsible choices and that is awesome. It lies down to individuals wanting to make that choice. I don't blame it on the fast food joints themselves."

Another nutritionist, Linda Outhwaite from Nutrition Wise, said the average calorie intake for a male adult should be between 2100-3500 calories daily and for a female between 1500-2500

"So consuming just over 600 calories in one item is not such a good idea. Most consumers will add a soft drink and fries adding another 3-400 calories to the meal," Ms Outhwaite said.

"The fat content in this burger is over half the total daily requirement for both men and women. Men require around 60g fat and women 55g on average.

Ms Outhwaite said saturated fat is one of the main contributors to high cholesterol levels, which can lead to hardened narrow arteries, increasing one's risk of high blood pressure, stroke and heart disease. Excess saturated fat intake is linked to cardiovascular disease, obesity and diet related cancers.

"Only 12 per cent of total fat intake should be from saturated fat which means around 7.6g for an average male and 6.6g for an average female daily. There are almost 12g in this burger and that is without fries," she said.

"Adolescents particularly need to be wary, as poor food choices during these growing years is the main contributor to obesity, followed closely by lack of exercise."

The Double Down will only be available for five weeks, costing $7.90 for just the burger and $10.90 for a combo.

Those queuing up tomorrow will "definitely not" be seeing Ms Turnbull in the line behind them.

"I like my food too much," she said. "I've got no desire to try one. Even if it were free."