The position of calories on menus appears to influence how much people eat, new research by the Economic and Social Research Institute (ESRI) suggests.

Obesity is increasing worldwide and this has led to calls for calorie information to be included on food menus.

As part of Ireland's Obesity Policy and Action Plan, the Government has said it is committed to introducing legislation on calorie posting. In the meantime, some restaurants are voluntarily putting calorie information on their menus. However, the size of this information and where it is placed on the menu differs across restaurants.

According to the ESRI, this could matter because research in behavioural economics suggests that, in general, the size, colour and location of information affects how people respond to it. It decided to look into this further.

The researchers carried out a series of carefully controlled experiments involving almost 150 consumers who were initially unaware that their food choices were being observed.

The experiments took place during weekday lunchtimes.

The participants ordered lunch from an online menu. One-third were randomly selected to see a menu with no calorie information, one-third saw a menu with calorie labels placed between the description of the food and the price (calories to the left of the price) and the one-third saw a menu that had calorie labels placed after the description of the food and the price (calories to the right of the price).

All of the menus were otherwise identical.

As the participants viewed the menus, their eye movements were recorded to see where on the menu they were looking.

After they had eaten their lunch, the researchers revealed that their choices had been part of an experiment and they were then asked to answer some follow-up questions.

The amount they had consumed was also measured, by weighing the food before and after.

The study found that people ordered and consumed less food when the calories were displayed on the right of the price.

Those who did not see any calories on the menu ordered an average of 866 calories and consumed 665. However when calories were displayed on the right, the participants ordered an average of 703 calories and consumed 421. This means they ordered 19% less calories and consumed 37% less, figures which the researchers consider "large and statistically significant".

The data on eye movements showed that consumers tended to look at more calorie information when it was on the right compared to when it was on the left.

Furthermore, consumers who saw calories to the right of the price were also more likely to know afterwards how many calories were in their meal.

The researchers found no difference in how much people enjoyed their lunch, despite the fact that some have suggested calorie posting could make consumers less likely to enjoy their food.

They concluded that their findings "provide clear evidence that exactly where calories are placed on menus matters".

"Controlled experimental studies like this can be used to pre-test policies before they are implemented. Opinions about calorie posting differ and can be strongly held, so it is important to provide objective evidence about the likely impact.

"Our results show not only that calorie posting changes behaviour, but also that seemingly small changes to the format influence how well people understand and respond to the information," commented the study's lead researcher, Dr Deirdre Robertson, of the ESRI's Behavioural Research Unit.