Some of the most popular products sold in New Zealand supermarkets are the least healthy.

These findings have emerged from an analysis of supermarket sales undertaken by researchers at The University of Auckland.

Full-fat milk, white bread, full-sugar soft drinks, butter and sweet biscuits proved the most popular choices within their respective food groups. Soft drinks featured six times in the top 30 products, and two sizes of cola drinks were among the top ten.

"The high sales of these products are contrary to national nutrition guidelines, which recommend eating less fatty, salty and sugary foods, eating wholegrain breads and choosing low-fat milk and milk products," note Sally Hamilton and colleagues in a paper published in the international journal Public Health Nutrition.

"Sugary drinks in particular have been under the spotlight recently for their contribution to the increasing rates of obesity. The findings from our supermarket sales data support this concern."

Reducing diet-related disease is a priority worldwide, says the paper, while improving nutrition is an objective of New Zealand's national nutrition strategy. "Measuring food consumption is necessary in order to monitor progress towards this goal."

Data on the top-selling 3000 food and non-alcoholic products bought by 882 customers who shopped regularly at a Wellington supermarket were gathered over a one-year period. Seventy-three percent of the customers were female and their mean age was 38.

Many of the researchers' findings were "broadly comparable" with data from national nutrition and food expenditure surveys. "Supermarket sales have the advantage of being an objective, convenient, up-to-date and cost-effective measure of household food purchases."

Supermarket sales did not, however, necessarily reflect total household diet with New Zealanders spending a quarter of their food budget on restaurant and café meals and takeaway foods. Nor did they identify which household members were eating what foods and how much, and how food was cooked or which ingredients were added.