Female body shape has a bearing on a wide range of human activities, and there are and have been widely different ideals of it in different cultures over history. The female figure is usually narrower at the waist than at the chest and hips, and usually has one of four basic shapes — banana, pear, apple or hourglass. The chest, waist and hips are called inflection points, and the ratios of their circumferences define these basic shapes. Body shape depends on skeletal structure and the distribution of fat and muscle in the body.
Some of these body shapes normally occur only in genetic women, although some endocrine conditions or deliberate use of female hormones, such as by transsexuals, can produce them in previously male bodies. As with most physical traits, there is a wide range of normal female body shapes.
The female body usually inflects inward towards the waist around the middle of the abdomen. The waist is smaller than the chest and hips, unless there is a high proportion of body fat distributed around the waist. How much the chest or hips inflect inward, towards the waist determines the structural shape.
Independent of fat percentage, weight or width, most female bodies have one of four elementary geometries, ordered by their commonality in western society. Banana or Straight: the waist circumference is at least 75% of the chest or hips circumferences, which are virtually the same. The body has a relatively high androgen level compared to the estrogen level, and this causes the skeleton to develop in a more masculine pattern and body fat to be distributed predominantly around the waist. Pear or Spoon or Bell (Triangle upward): the waist circumference is at least 75% of the chest circumference, and the hips circumference is at least 110% of the chest circumference. The distribution of fat varies, with fat tending to deposit first in the buttocks, hips and thighs. As body fat percentage increases, an increasing proportion of body fat is distributed around the waist and upper abdomen. Apple (Triangle downward): the waist circumference is at most 75% of the chest circumference, and the chest circumference is at least 110% of the hips circumference. Body fat distribution tends to begin in the arms, shoulders, chest and upper abdomen first. Hourglass shape (Triangles opposing, facing in): the waist circumference is less than 75% of the chest or hips circumferences, which are virtually the same. Body fat distribution tends to be around both the upper body and lower body. This body type enlarges the arms, breasts, hips and rear before other parts, including waist and upper abdomen. Due to the preference shown to physical symmetry, many celebrities falsely claim hourglass measurements but actually rate closer to a straight figure or apple.
A study of over 6,000 women carried out by researchers at the North Carolina State University around 2005 found that 46% were Banana (rectangular), just over 20% Pear, just under 14% Apple, and 8% Hourglass.
New research suggests that hourglass women may live longest, and apple-shaped the shortest.
The inflection points on the female form define a woman's combinational structure. Any structure can occur in a range of proportions.
Body Mass Index, which considers only height and total mass, is an approximate method for calculating whether an adult is overweight, underweight, or of a healthy weight. Some recent research indicates that the waist-hip ratio is a better measure of obesity than body mass index, particularly for the purpose of determining risk of heart attack. The ideal ratio for women is about 0.7. The body fat percentage is considered to be an even more accurate measure of obesity. Of these three measurements, only the waist-hip ratio uses dimensions that will vary depending upon the body structure. Hence, it is possible for two women to have vastly different body mass indices but the same waist-hip ratio, or to have the same body mass index but vastly different waist-hip ratios.
The ideal female body size and shape varies among cultures; however, the preference for a small waist has remained fairly constant throughout history. A low waist-hip ratio has often been seen as a sign of good reproductive potential, but recent research suggests that attractiveness is more correlated to body mass index than waist-hip ratio, contrary to previous belief.
Many societies vary on their contrasts, criticisms and praise of the female form. Crowd leaders, such as celebrities, also impact the "desirable" female body shape.
Many "curvy" American film stars from the early and mid-20th century are cited as inspirations by overweight women when, in reality, they were thin even by today's standards. Marilyn Monroe is said to have worn a size 16 dress. However, this fails to consider the changes in American garment sizing over the last century. Monroe was 5'5", weighed 118 lbs and measured 36-24-34, which would make her approximately a women's size 2 by modern American sizing standards.
Sociocultural studies highlight the role of cultural factors in the incidence of anorexia nervosa in women, such as the promotion of thinness as the ideal female form in Western industrialised nations, particularly through the media. A recent epidemiological study of 989,871 Swedish residents indicated that gender, ethnicity and socio-economic status were highly correlated with the chance of developing anorexia, and women with non-European parents were among the least likely to be diagnosed, while women in wealthy, ethnic Swedish families were most at risk.
A classic study by Garner and Garfinkel demonstrated that those in professions where there is a particular social pressure to be thin (such as models and dancers) were much more likely to develop anorexia during their career, and further research suggests that those with anorexia have much higher contact with cultural sources that promote weight-loss.
Although anorexia nervosa is usually associated with Western cultures, exposure to Western media is thought to have led to an increase in cases in non-Western countries. But other cultures may not display the same worries about becoming fat as those with the condition in the West, but instead may present with low appetite with the other common features.