They're calling for the Government to step in and regulate the industry, with more labelling, food composition targets and serving size guidance.
Fast food was "heavily marketed, cheap in comparison to other restaurant foods, convenient, accessible and palatable", they wrote. It was also linked with accelerating rates of weight gain and obesity.
That's a major issue in New Zealand, where two out of three adults are overweight or obese, as are three out of 10 children.
The study, published recently in the journal Nutrients, used information gathered over February and March 2020, looking at serving size and nutrition information, comparing kilojoules, sodium (salt), sugar and saturated fat with recommended daily intake.
Burgers were typically the highest-energy item, followed by fries and "Asian meals", while salt was usually highest in burgers, followed by breakfast items, savouries and sandwiches and wraps.
But there was huge variation in some categories - such as burger sizes that ranged from 101 grams up to 718g.
The median energy content of a combo was 4381 kJ - which means half of the combos contained at least half of the recommended energy intake for a New Zealand adult (8700 kJ).
The worst offender was a double burger with dessert, fries and a sugary soft drink, which included 16 teaspoons of sugar and contained more salt and kilojoules than the average adult needs in an entire day.
The researchers did not name the fast food chain responsible, saying they didn't want to single out one company.
That meal had more than three times the calories, over twice the salt, and 13 times the sugar of a combo meal consisting of a cheeseburger, small fries and a no-sugar soft drink.
The researchers found 92 per cent of sugar-sweetened soft drinks on offer would have to pay a sugar levy if they were in the UK, while half the smoothies analysed provided an entire day's worth of sugar.
Excess sodium was also a concern in many of the products - every product in the "fries" category exceeded the UK's sodium target for out-of-home foods, as did more than half of pizzas and savoury pastries.
So, what's the takeaway for consumers?
"Even when you're going for the convenience of a combo meal, your exact choice can make a big difference for your health," lead researcher Dr Sally Mackay said.
"Go for smaller portions, skip the dessert, and choose a low-sugar drink, and you'll see the benefit for your wallet as well as your body."
The study had aimed to look at all fast food chains with 20 or more stores across New Zealand, but seven chains were excluded as researchers could find no nutrition information in store or online.
Mackay said it was disappointing that most takeaway chains failed to provide nutrition information for most products, and some provided none.
They called for the Government to set serving size guidance, sodium targets and nutrition labelling rules - the latter of which is currently being considered by policy makers. They also wanted the Government to ensure the voluntary recommendations of the 2018 Food Industry Taskforce are implemented.
FAST FOOD CHAINS IN THE STUDY
Products and combos were analysed from 20 fast food chains: Burger Fuel, Burger King, Burger Wisconsin, Domino's Pizza, Hell Pizza, Jester's Pies, KFC, McDonald's, McCafé, Muffin Break, Noodle Canteen, Pita Pit, Pizza Hut, St Pierre's Sushi, Subway, Tank Juice, Wendy's, Wild Bean Café, Wishbone and Z Express.
CHAINS EXCLUDED DUE TO NO NUTRITION INFORMATION
Nando's, Night 'n Day@Gull, Sal's Pizza, Shake Shed and Co, Shamiana, Starbucks and The Coffee Club were excluded from the study as the researchers could find no nutrition info online or in store.
