We make food decisions several times a day -- from what time we eat to how much -- but a new University of Otago, New Zealand, study has found we are not very good at judging the energy-density of what we consume.

Lead author Dr Mei Peng, of the Department of Food Science, says inaccurate judgements about food energy and/or portion size can lead to overeating and subsequent weight problems.

"It is very important to understand how people make these decisions, particularly in the current food environment, where foods are more accessible, palatable and energy-dense than ever.

"There is already a large body of literature suggesting that people can vary considerably in terms of knowledge about food, but there is little understanding about how people differ from one another when making subconscious decisions about food," she says.

The research, supported by the Marsden Fund and just published in Appetite, was carried out in conjunction with Associate Professor Ami Eidels of the University of Newcastle, Australia.

The group studied how 70 people made decisions between food energy and portion size and found people 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.

"Although people are generally good at differentiating high-calorie foods from low-calorie foods, this judgement 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'," Dr Peng says.

As many of the available health guidelines are based on portion sizes, the researchers believe people need to be better informed about food energy content.

Dr Peng believes more explicit and salient energy labels on food packages might be one of the possible methods to help people to make better decisions.

"It is very important for us to make deliberate effort to plan our meals and snacks to ensure we don't overeat.

"Relative to controlling food portions, paying close attention to food calories, and making good food choices are possibly more important for weight maintenance or weight loss."