Overweight women tend to end up with lower-quality mates - but excess kilos are no disadvantage for men, a psychologist has found.

Dr Alice Boyes, a New Zealander who returned from Britain six months ago to rejoin her partner in Christchurch, says heavier women pair with men who give themselves low ratings on scales of "attractiveness/vitality" and "status/resources".

But men's weight makes no statistically significant difference to their partners' ratings of themselves on any of the three scales used - attractiveness/vitality, status/resources and warmth/trustworthiness.

"For women the standards are much more restrictive," Dr Boyes said yesterday.

"A woman with a wee bit of a round tummy might be judged negatively. There is a bit of a bias there."

Her study, just published in the American Journal of Sex and Marital Therapy, was drawn from a wider set of questions about relationships in a sample of 57 couples at Canterbury University who were interviewed for her 2006 doctoral thesis.

She asked women and men to rate the quality of their relationships, whether they expected them to last, and how they rated themselves and their partners on 17 qualities grouped under the three scales of attractiveness/vitality, status/resources and warmth/trustworthiness.

"For a long-term relationship, both women and men value warmth/trustworthiness the highest," she said.

"To men, attractiveness/vitality is a lot more important than status/resources, but for women it's more even."

She found that the higher the woman's body mass index, the lower the quality of their relationships as rated by both the women and their partners, and the less secure both partners felt.

Partner ratings:

Warmth/trustworthiness: understanding, supportive, kind, good listener, sensitive, considerate.

Attractiveness/vitality: sexy, nice body, attractive appearance, good lover, outgoing, adventurous.

Status/resources: successful, nice house, financially secure, dresses well, good job.

* aliceboyes.com