Do you want fries or salad with that? We all know the right answer but given the choice, most of us will opt for the fries, says new research into consumer behaviour.

It would appear that as restaurants and vending machine operators grant us our wish for health food options, we are more likely to order the least healthy option, say researchers with City University of New York and Duke University.

A study released this month in the Journal of Consumer Research suggests we are in fact our own worst enemies when it comes to making healthy food choices.

"Just because we consumers want to see healthier items available does not mean that we are going to choose them," write the authors.

"We present evidence that for many consumers, the addition of healthy alternatives to food choice sets can, ironically, increase the consumption of very indulgent food items."

In the study, more than 100 college students were randomly assigned to be presented with one of two menus.

The first menu offered a choice of french fries, chicken nuggets and a baked potato while the other included those same choices, but with the addition of a salad.

The researchers found that those participants with the greatest levels of self-control, as measured by a battery of psychological tests, were three times more likely than those with low self-control to choose the fries when given a menu that included salad.

"As we predicted, when given the choice of fries, chicken nuggets, or a baked potato, people high in self-control rarely chose the fries, which are considered the least-healthy option in the set.

"However, add the salad to the set and what happens? High self-control individuals were significantly more likely to choose the french fries," the authors write.

The authors suggest their finding shows that merely presenting a healthy option vicariously fulfils health-related eating goals, drives attention to the least-healthy choice and provides people with licence to indulge in tempting foods.