There's one easy way to cut back on your household spending, suggest researchers -- find out when the ladies of the house are most fertile.
Yes, the menstrual cycle doesn't just bring on cramps, bouts of irrational fury and a deep need for large bowls of pasta. It also influence women's shopping patterns.
Researchers at Concordia University in Canada have investigated how a woman's menstrual cycle impacts her consumption desires, product usage, and money spent on food and 'beautification', such as buying cosmetic products.
Gad Saad of the John Molson School of Business led a team that tracked the behaviour of 59 female participants for just over one month.
The women were asked to kept detailed diaries that chronicled beautification behaviours, clothing choices, calorie consumption, and purchases.
Respondents were asked to what degree they wore clothes to attract sexual attention, spent time making themselves beautiful, sun bathed, and ate highly caloric foods, on each day. And a distinct pattern soon emerged.
There was a marked increase in women's appearance-related behaviours during the fertile phase of the menstrual cycle (roughly days eight to 15 of a 28-day cycle). Women were also more likely to spend more money on clothes during the fertile phase.
There are Darwinian reasons at work here, explains Saad.
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"In ancestral times women had to focus more time on mating-related activities during the fertile phase of the menstrual cycle, when the likelihood of conception was highest.
"Those same psychological and physiological mechanisms now lead women to engage in greater consumption of products relevant to reproductive drives during the fertile phase of their cycle," he said, in a statement.
When it came to food, however, there was a distinct dip in consumption.
During the luteal (infertile) phase, women crave, buy and consume more highly caloric foods.
Evolutionary forces are at work here too, says Saad. "Women consume more calories during the luteal phase because they've evolved mechanisms that favoured non-mating-related activities like food foraging."