Image copyright Science Photo Library Image caption Study participants were asked to learn and predict the appearance of food reward cards

Obese women may have a "food learning impairment" that could explain their attitude to food, research from Yale School of Medicine suggests.

Tests on groups of obese and healthy-weight people found that the obese women performed worst when asked to remember a sequence of food picture cards.

Writing in Current Biology, Yale researchers tested 135 men and women.

The findings could lead to new ways to tackle obesity, the study says.

Study author Ifat Levy, assistant professor at Yale School of Medicine, said the difference in the performance of the obese women compared with the other groups was "really striking" and "significant".

The tests looked at an individual's ability to learn and predict the appearance of pictures of food or money on coloured cards.

The participants were told they would be given whatever appeared on these "reward" cards.

In the first phase, the reward cards always followed a particular coloured card in a sequence. Later, the order was changed and the reward cards appeared following a different coloured card.

An intriguing possibility is that, by modifying flawed association between food and environmental cues, we may be able to change eating patterns Ifat Levy, Yale University

During this time, participants were asked to predict the likelihood of a reward card appearing as the cards were shown one by one.

The results showed that obese women performed worst because they overestimated how often the pictures of food, including pretzels or chocolate, appeared.

Even after researchers had accounted for other factors, there was still a large difference in their learning performance.

Prof Levy said: "This is not a general learning impairment, as obese women had no problem learning when the reward was money rather than food.

"An intriguing possibility is that, by modifying flawed association between food and environmental cues, we may be able to change eating patterns."

The study said it was not clear what lay behind the learning deficit in obese women.

In contrast, obese men did not show any signs of a food learning impairment.

Body image

The study suggested that women who are obese act this way because of particular concerns about food or because they feel more unhappy or dissatisfied about their body image.

Previous research suggests that there are differences in how men and women perceive obesity.

Future research is likely to focus on whether the food-specific learning problem is a result of obesity or a potential factor in causing obesity by testing individuals before and after weight loss.

The Yale researchers said their results called for a shift in focus.

"Rather than target these individuals' behaviour with food, we suggest that a successful intervention should aim to modify their interactions with other cues that determine their eating patterns," they wrote.