If you've ever been surprised by the sudden emptiness of a greasy pizza box well there's good reason for it: turns out food tastes too good now and we can't stop eating it, even when we've had enough.

So-called "hyper-palatable" foods have been identified by researchers as one of the key culprits behind obesity, thanks to a cocktail of sweet, salty, fatty ingredients that light up reward systems in the brain and overpower signals that try to tell us we've had enough to eat.

While the report, published in the Obesity journal this week, analysed the American diet, similar lifestyles, incomes and good old fashioned cultural imperialism means the Australian diet contains many of the same ultra-processed, pre-packaged, and fast food that have made the United States the fattest country in the world.

38.2 per cent of US adults are obese, according to the latest obesity update from the Organisation for Economic Co-operation and Development (OECD).


Us Australians, for reference, are fifth on the OECD list with 27.9 per cent, but we could actually be higher, with more recent figures from the Australian Institute of Health and Welfare stating 31 per cent of us are obese, and a further 36 per cent overweight.

While the concept of hyper-palatable foods isn't new, the team behind the research said they aimed to provide a standardised definition of what puts a food product in that class.

"Multiple documentaries have pointed out that food companies have very well-designed formulas for these types of foods to make them palatable and essentially enhance consumption," said University of Kansas assistant professor of psychology and lead author of the research, Tera Fazzino.

"But these definitions are virtually unknown to the scientific community, which is a major limitation … we've just typically used descriptive definitions like 'sweets,' 'desserts' and 'fast foods'," she added.

Ms Fazzino said it was important to address this limitation to provide a standardised definition that can be used to compare multiple studies.

The researchers studied close to 8000 different food products, then used software to compare the nutritional information of the food to known combinations where the ingredients together produced an "artificially enhanced palatability" than either would produce alone.

The three combinations were fat and sodium (for instance, bacon), fat and sugar (like ice cream and baked goods), and carbohydrates with sodium (like chips and popcorn).

Some foods — predictably the most delicious ones — contain all three, for instance a pepperoni pizza has fatty cheese, salty meats and sweetened tomato sauce on a carb-loaded base.


The three combinations were then used to determine how much of the American diet was made up of these hyper-palatable foods.

The researchers found almost two-thirds — 62 per cent — of the foods in the US Department of Agriculture's Food and Nutrient Database for Dietary Studies contained at least one of the combinations.

The team also found further proof that healthy labelling on foods doesn't mean much, with 5 per cent of the foods identified as hyper-palatable being labelled reduced or no fat, sugar, salt or calories.

Of all the food in the database bearing a label declaring low/reduced/no sugar, fat, sodium, and/or sugar, just under half of them could be classed as hyper-palatable.

Ms Fazzino said the research could offer guidance to the government to warn citizens about the health dangers in overly processed foods

"If research begins to support that these foods may be particularly problematic for society, I think that could warrant something like a food label saying 'this is hyper-palatable,'" she said. "We might even think about the restriction of certain types of foods that are available in certain places — for example, in elementary school cafeterias for kids whose brains are still developing and who may be impacted by these types of foods."

Ms Fazzino's next plan involves analysing how the abundance of hyper-palatable foods in the American diet compares with others around the world.

Her first target is southern parts of Italy, where she plans to compare the US diet made up of ultra-processed foods with the Mediterranean diet, which centres around whole foods, unsaturated fats and fish.