Researchers have recommended more obvious energy labels on food packaging after finding some people have trouble estimating calorie contents.
A joint study by researchers at the University of Newcastle and University of Otago, New Zealand, showed the 70 participants were good at assessing food quantities but not the energy density of food.
"We were particularly surprised to see substantial variations across people for judging food calories," lead author Dr Mei Peng, of the Department of Food Science at the University of Otago, said.
"Although people are generally good at differentiating high-calorie foods from low-calorie foods, this judgment process appears to be more intuitive for some than others.
"For some people, if a high-calorie food is presented in a small quantity, it appears to be less unhealthy."
The researchers believe people need to be better informed about food energy content given many health guidelines are based on portion sizes.
Dr Peng said more explicit and visible energy labeling on food packages was one possible way to encourage better decisions.
The study, published in the journal Appetite, involved Associate Professor Ami Eidels and his colleagues and students at Newcastle Cognition Lab in the University of Newcastle's School of Psychology.
The lab uses mathematical and computational methods to gauge how people process multiple sources of information to make decisions, in this case in the context of food choices.
