Image caption Do men seek the comfort of a "motherly" figure when put under pressure?

When placed under stressful situations, men rate larger women as more attractive, new research has shown.

British researchers found that men exposed to tasks that were designed to put them under pressure preferred a wider range of female body sizes.

They conclude that stress can act to alter judgments of potential partners.

The work by a team from London and Newcastle is published in the open access journal Plos One.

"There's a lot of literature suggesting that our BMI (body mass index) preferences are hard-wired, but that's probably not true," co-author Dr Martin Tovee, from Newcastle University, told BBC News.

Changing the media, changing your lifestyle, all these things can change what you think is the ideal body size Martin Tovee, Newcastle University

Dr Tovee and his colleague, Dr Viren Swami, have previously researched what factors could alter BMI preferences, including publishing a paper in the British Journal of Psychology on the effect of hunger, and the influence of the media.

But through this new work they aimed to investigate whether known cross-cultural differences in body size preferences linked to stress were also mirrored in short-term stressful situations.

"If you look at environments where food is scarce, people's preferences for body size in a potential partner are shifted. [The preference] appears to be much heavier compared to environments where there's plenty of food and a much more relaxed atmosphere," he explained.

"If you're living a far more stressful, subsistence lifestyle, you're going to have higher stress levels."

To simulate heightened stress, a test group of men were placed in interview and public speaking scenarios and their BMI preferences compared against a control group of non-stressed men.

The results indicated that the change in "environmental conditions" led to a shift of weight preference towards heavier women with the men considering a wider range of body sizes attractive.

Flexible preferences

"These changes are comparatively minor in comparison to those you get between different [cross-cultural] environments. But they suggest certain factors which might combine with others and cause this shift," Dr Tovee said.

The research supports other work that has shown perceptions of physical attractiveness alter with levels of economic and physiological stress linked to lifestyle.

"If you follow people moving from low-resource areas to higher resource-areas, you find their preferences shift over the course of about 18 months. In evolutionary psychology terms, you try to fit your preferences to what works best in a particular environment," said Dr Tovee.

Moreover, the researchers were keen to emphasise how fluctuating environmental conditions could alter the popular perception of an "ideal" body size.

"There's a continual pushing down of the ideal, but this preference is flexible. Changing the media, changing your lifestyle, all these things can change what you think is the ideal body size," he said.