Making poor food choices has nothing to do with access and price, but affordability, with economic constraints the biggest factor in determining what people will put in their shopping trolley.
Australian and New Zealand-based research shows food is both abundant and relatively equal in terms of quality, cost and availability, but those on lower incomes spend more of their cash to feed themselves.
The issue of the cost of good nutrition and the stress affording food can cause, will be discussed at the Dietitians New Zealand national conference in Dunedin this week.
Flinders University School of Medicine associate dean Prof John Coveney said there were assumptions that poorer people did not eat healthy foods because they did not have the knowledge to eat well, and did not have access to healthy food.
However, Prof Coveney studied the availability and cost of healthy food in metropolitan Adelaide by comparing prices of a 52-piece "healthy food basket" and found "there was no difference in the price of food in high income or low income areas".
"We could not say healthy food was more expensive in low income areas, nor was it less available."
The problem arises in the affordability of the healthy food basket.
Those on high incomes spent just 9% of their income on healthy food, compared with low earners, who spent about 30% of their income.
"A lack of support to manage such a tight budgetary situation results in `food stress'," he said.
Making healthy food cheaper would encourage people to eat better.
"We need to make healthy choices easier, and unhealthy choices harder."
This belief was backed by "the most important" public health study done in the last 15 years - the Supermarket Health Options Project, which was conducted in New Zealand and led by the University of Auckland in 2008 and 2009.
The project found if the price of healthy food was reduced by 12.5%, people would buy more of it.
On the other hand, tailored education about nutrition had no impact.
He also believed a "fat tax" would not be helpful, because disadvantaged people tended to eat more fast foods and taxing such food would only further disadvantage them, he said.
This disadvantage resulted in lower "food security" for lower socio-economic households, as University of Otago nutritionist and PhD student Claire Smith found.
Food security relates to a person's ability to access enough food to live an active and healthy life.
Ms Smith's Family Food Environment Survey, conducted in Dunedin and Wellington in 2007 and 2008, found 60% of New Zealand households were food secure, 30% were moderately secure, and 10% had low food security.
People with moderate to low food security often limited variety and decreased the quality of the food they ate, ran out of some food, became stressed, decreased the quantity of food they ate, and began to rely on foodbanks or family and friends for support.
As the impact of the recession continued to hit, food security was becoming an increasing problem, with pressure on foodbanks growing.
There is a higher prevalence of food insecurity in low-income households, single-parent households, those in which Government benefits were the main source of income, and those in rental accommodation.
Expenditure on food was reduced in order to pay rent and bills in 52% of low or moderate food security households she studied.
The amount an adult female spent on food in a secure home was $55.64, compared to $45.13 for an insecure one.
The amount spent on vegetables in a secure home was $4.49, compared to $3.16 in a insecure home.
Fresh fruit was $4.36 in a secure home, and $3.32 in an insecure one.
Interestingly, a moderate food security household would spend $8.60 on snacks, cakes, biscuits and non-alcoholic beverages, compared to $3.54 in a low food security household.
"They weren't spending their money on empty calories."
Removing GST from all foods, not just healthy foods, would be "great", she believed.
"Few behavioural changes will impact on the issues, unless financial constraints are addressed."