Dr Luca Serventi of Lincoln University runs Stuff through the current state of the industry.

The $1 loaf sits unadorned at one end of an aisle in every supermarket across the country. The basic packaging makes no pretence about what the buyer is buying.

Its label makes no bold claims about nutritional benefits or artisan origins. It is cheap, white bread, pure and simple.

But it is a loaf packed with financial muscle. Since its introduction four years ago, the $1 loaf has been either the second or first most-bought product in Countdown supermarkets, jostling with bananas for top spot.

Within a year of introducing the $1 loaf to its aisles in July, 2014, Countdown had sold 19 million of them.

At the time of the launch Countdown couched the $1 loaf almost as an act of charity. "Price is important to Kiwis, no matter who they are or where they live," managing director Dave Chambers said.

"We can't impact the cost of our customers' rent, mortgage or their power bill, but we have listened to what our customers want and can help families manage the cost of their shopping by delivering better value every day, like a loaf of bread."

It's hard to argue that the $1 loaf is going to be about the cheapest source of energy you can find – it packs 1400 calories, so if you were of a mind to eat a whole one, you'd be consuming up to 70 per cent of your required daily intake.

ALDEN WILLIAMS/STUFF The Value loaf - plain, white and cheap at a supermarket near you.

You may not be getting much more in the way of benefits, though.

Bread scientist Luca Serventi, lecturer in life sciences and agriculture at Lincoln University, explains that white bread's nutritional benefits are minimal.

The $1 loaf is pure starch, which converts to sugar in the body – the body needs carbohydrates for energy. There are none of the minerals, fibre or protein that may be present in other more expensive breads.

ALDEN WILLIAMS/STUFF In every supermarket bread aisle you're bound to find the $1 loaf nestled among the more glamorous brands.

"It's less nutritious but it's not harmful. If you are on a lower budget then it's a perfectly reasonable choice," Serventi says.

"You're introducing less minerals, less fibre and protein but basically a good source of starch. There's plenty of energy which is the main thing our body runs on, so that's excellent."

However he adds: "White bread quickly spikes our blood glucose so, if consumed daily, it may increase the risk of diabetes."

If there's not a lot of nutritional benefit in a $1 loaf, there's clearly not much profit, either.

ALDEN WILLIAMS/STUFF Lincoln University professor Luca Serventi says a $1 loaf won't do a lot for your nutritional needs, but it's at least a cheap source of energy.

Peter Rewi, the president of the New Zealand Association of Bakers, which represents both Goodman Fielder and George Weston who make the bulk of the branded bread in New Zealand supermarkets, acknowledges: "$1 bread is a good value for money product for the consumer, but is unprofitable for bakers".

Norm Holley, the secretary for the NZ Bakers and Pastrycooks Union and an ex-baker himself, sees it in starker terms. Given the cost of raw ingredients, labour and all the overheads of getting bread to the market, "there shouldn't be a loaf of bread in New Zealand under $1.80", Holley claims.

The bakeries can't make sufficient profit on $1 loaves, which he says impacts on the wider economics of the industry. He laments the power of the supermarkets to demand suppliers stick with producing bread at a price which threatens the viability of the bakeries.

ALDEN WILLIAMS/STUFF A line-up of familiar bread brands.

Unsurprisingly, the supermarkets stand by their pricing and supply methods. And of course, once Countdown launched its $1 loaf, its arch-rival Foodstuffs (New World and Pak 'n Save) wasn't far behind.

"Back in 2014 we had been looking into developing a super-sharp bread offer and heard that our competitor was also exploring a bread deal," Foodstuffs' spokeswoman Antoinette Laird says.

"As a 100 per cent New Zealand-owned company, we were determined we weren't going to give our offshore rivals an inch so we accelerated our plans to launch at the same time. At the end of the day our customers end up the winners.

"Bread is a key category and we're experiencing lots of change, innovation and growth; both from our suppliers and in-house teams," Laird says.

As for the big bakeries themselves, they're not keen to reveal much about what goes into a $1 loaf.

Both George Weston and Goodman Fielder declined Stuff's request for a look at the baking operation which churns out thousands of loaves of cheap, unglamorous, plain, white bread each week.