We make 35,000 decisions every day and when it comes to groceries we make our choices in a hurry.
In an average Countdown supermarket there are 20,000 products and retail experts estimate we spend around five seconds deciding on each item we put in our trolley.
AUT's Dr Marilyn Giroux studies consumer behaviour and she says the latest retail practice preys on our lack of attention to detail.
"One of the current trends that we are seeing is over packaging,
"The bigger it looks, the more people are willing to buy it," Dr Giroux says.
Dr Giroux says chips are a common example.
"I want a full bag of chips, but only 50 per cent of it (the packet) is actually chips."
"We're really not good at making rational decisions. We base it (buying) on emotions a lot of time, base on colours, how big something is."
Over packaging is legal. Food is measured by weight not volume.
The food companies disagree. They say the over packaging allows the product to settle.
Bluebird, for instance, say there’s packaging is full of hydrogen, not air.
"Without it the chips would go stale and it's there to protect them in transportation," a spokesperson said.
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