Glance through any contemporary fashion magazine and it becomes clear that what is beautiful is also slim, perhaps even dangerously so.For example, Tovée and his colleagues (1997) compiled the biometric measurements of 300 fashion models and 300 glamour models, and found that they were consistently underweight in terms of BMI.For most women, fat (or adipose tissue) deposit is inhibited in the abdominal region and stimulated in the gluteofemoral region (buttocks and thighs) more than any other region. This engenders what is known as a ‘gynoid’ fat distribution.For most men, on the other hand, fat deposit is stimulated in the abdominal region and inhibited in the gluteofemoral region. It is this sexually dimorphic body fat distribution that underscores body shape differences between the women and men, and is typically quantified by measuring the ratio of the circumference of the waist to the circumference of the hips. This hip measurement is known as the waist-to-hip ratio (WHR), and closely related to the classic ‘hourglass’ figure in women.For healthy, pre-menopausal Caucasian women, the range of WHRs have been shown to be between 0.67 and 0.80. Women typically maintain a lower WHR than men through adulthood, although the WHR approaches the masculine range after menopause. This increase in WHR is most likely caused by the reduction in estrogen levels, which increases fat deposit in the abdominal region.This interpretation is corroborated by studies showing that, when women and men are administered estrogen compounds, their WHRs tend to become lower over time.In short, then, there are sex-typical differences in the pattern of fat distribution as a function of the sex hormones. Combining this with an evolutionary psychological approach, Singh proposed that the risk for various disease depends not only on the degree of obesity as measured by BMI, but also on the anatomical location of fat deposits. In other words, the WHR is symetrically related to a variety of life outcomes, with a low WHR being associated with better outcomes in women.In addition, Singh argued that the WHR signals all the conditions that affect women’s reproductive status. Women with higher WHRs have more irregular menstrual cycles, and the WHR becomes significantly lower during ovulation compared to non-ovulatory phases of the menstrual cycle. The probability of successful pregnancy induction is also affected by WHR: women participating in donor insemination programmes have a lower probability of conception if their WHR is greater than 0.80, after controlling for age, BMI and parity.MORE: How Weight and Waist-to-Hip Ratio Relate to Health Married women with a higher WHR also have more difficulty becoming pregnant and have their first live birth at a later age than married women with lower WHRs. On the basis of such evidence, Singh concluded that women’s susceptibility to various major physical diseases and fertility is reliably conveyed by the size of the WHR.VIDEO: Interpreting your Waist Measurement