Fast food outlets are hailing the inclusion of wraps and salads in menus, but according to research, the overall trend is towards a growth in less healthy products.
The University of Auckland study, "Fast Food Trends in New Zealand" looked at 10 fast food chains, including Burger King, Domino's Pizza and McDonald's, using information available at branches and on the companies' websites.
It found that between 2012 and 2016 serving sizes across all products grew by 5 percent, along with a 12 percent increase in sodium per serve.
RNZ contacted several fastfood outlets for comment, including McDonald's, Burger King and KFC, but no response was received.
The figures were presented at a symposium in Wellington today looking at how this country can tackle diet-related diseases.
Dr Helen Eyles led the research and said, as well as the portion size and salt-content increasing, the energy in each serving also rose by 13 percent during the 5 years of the study.
She said that was equivalent to the energy found in half a banana or half a muesli bar added to meals.
"It might not seem that much, but if you have that added to your burger, added to your fries, added to your beverage, that could add up quite considerably."
University of Otago human nutrition and medicine professor Jim Mann said the larger portion sizes were reflected in New Zealand's presence near the top of world league tables for obesity.
"What people don't realise is that about 10 years ago we were roughly on a par with countries like the UK, Finland and Canada, but since then we have rapidly increased," prof Mann said.
"So while obesity rates have increased in some of those countries, we are [now] streets ahead of them in terms of our obesity rates."
Dr Eyles said it was important that action be taken soon, because as people's weight increases, so does blood pressure and the risk of heart disease and other illnesses.
Some food manufacturers have indicated they were interested in reducing salt and sugar content and some of the bigger companies were reformulating their products but it was not enough, Dr Eyles said.
The World Health Organisation has set a target for countries to reduce their salt consumption by 2025 and that could be met if some nutrition targets were set for fast food manufacturers here, she said.
"[They] would be phased in over time, so they'd meet a certain standard and then we'd reduce them further and then further until we meet the target, so ... manufacturers have a realistic target to meet in the short term and that gets extended out over time."