Making Babies: Why Bigger is Better
When Rose E. Frisch began her research over twenty years ago, there was little interest in the subject of a woman's menstrual cycle and its connection to body fat. In fact, few knew that there was a connection, or cared to explore the idea. However, Frisch, a professor in population sciences at the Harvard School of Public Health, began receiving phone calls in the mid-seventies from women who were having fertility problems. Frisch saw a growing connection among women who were unable to conceive and their extremely slim, lean build (2, p. 14-15). Over the years, an increasing number of studies have examined the relationship between a woman's body fat percentages, its connections to fertility rates, and the effects on the menstrual cycle. Frisch's research, along with that of her colleagues, shows that there is a minimum weight according to one's height that will allow you to maintain a regular period, and therefore have children. While this may seem to be a simple concept, it was one very new to the scientific community thirty years ago, and has effected much of the way the female menstruation cycle is viewed today. More specifically, the focus has been on female athletes and the greater implications of losing one's period, including disordered eating, and loss of bone density. The relationship between body fat and one's ability to produce offspring has become an integral part of the study of women's health.
In the most simplest explanation, having a very low percentage of body fat will render a female unable to menstruate and therefore have children. There is also evidence on the other end of the spectrum that an extremely obese woman, with a high percentage of body fat, will also experience reproductive complications. To put things in perspective, the average body fat percentage for a woman is between 26 and 28 percent. As a woman ages, it can rise to 30 or 40 percent. In contrast, an average male only possesses 12 to 14 percent of body fat. Essentially, a non-overweight woman can have approximately 35 pounds of fat on her body (2, p. 4). It is this major difference between men and woman that allows a woman to become pregnant and bear a child, however too much or too little can have detrimental effects. While a woman can control her period by changing her dietary patterns and her body fat percentage, changes are taking place at a more complex level.
The hypothalamus is the part of the brain that controls reproductive ability, food intake, and energy metabolism (2, p.17). It is responsible for secreting the Gonadotropin- releasing hormones (GnRH) into the blood stream, which act as "go" signals for the body to being puberty (2, p. 48). The GnRH is a small peptide comprised of ten amino acids, and pulses in a pattern which triggers ovulation each month. The secretion of GnRH in prepubescent girls is very low, preventing them from having a period until adolescence. In 1994, the hormone leptin was found to be the trigger for the hypothalamus to begin the secretion of GnRH, it signals the body that the female is grown-up enough to have a baby, and therefore starts menstruation. Leptin is made by body fat and plays a key role in regulating food intake and energy metabolism. It wasn't until 1997 that leptin was linked with the onset of puberty and menstruation, but it had already been recognized as a factor in controlling body fat (1). This is where the two ideas really came together and demonstrated the connection between a woman's body fat and her ability to have children. As Frisch writes, "If girls or women lose weight so that their body composition reverts to the prepubertal ratio of high lean mass to low body fat the GnRH secretion also reverts to the prepubertal, 'non-go' pulse patter. Weight gain restores the pulsatile secretion of GnRH to adult levels and frequency" (2, p. 49). Therefore, it is extremely important for a girl to reach a certain weight before her brain feels that she is capable of sustaining a pregnancy, which is why a young girl's period often starts directly following her growth spurt, the average age being 12.5 years old at present.
The hypothalamus has been shown to be very sensitive to even small differences in a woman's relative fatness. Women have been known to "turn on" and "off" their periods with the gain or loss of only a few pounds. These are women on the cusp of their minimum weight for getting their period, and even a small change in their diet can affect how they menstruate. This leads to the growing concerns about female athletes today, many of whom live well below their minimum body fat ratio and experience drastic side effects. The female athlete triad was a phrase coined in 1992 to express the three major problems among female athletes, all of which are interrelated. It includes disordered eating, a suspended menstrual cycle, and premature bone loss (4). These three things are extremely detrimental to a woman's overall health, and many coaches are starting to be trained in recognizing the symptoms (3). There are certain sports that are more affected than others, studies have found, for a variety of reasons. In swimming and track, body weight can have a significant impact on one's scores, and has led to the close monitoring of females' diets and body fat percentages who participate (3). Also, sports that are judged subjectively and favor a prepubescent body shape for women are at high risk, for example, gymnasts, figure skaters, and divers. These sports also tend to draw athletes very prone to eating disorders in the first place, because of their intense, controlling personalities and extreme attention to detail. In 1994, the problem with women in these particular sports, and female athletes in general, came to national media attention with the death of 22 year-old world-class gymnast Christy Henrich, who was 4-foot, 11 inches, and weighed 60 pounds at the time of her death. She suffered from anorexia nervosa and bulimia, and died from multiple organ failure (4).
When an athlete loses her period, it is not necessarily that she is not eating, however. As Doctor Hoch reports in the New York Times this past September, "What we know from research is that women can exercise as much as they want, they can run 100 miles a week and if they fuel themselves properly, the will have normal periods" (4). This becomes a very serious issue then, if a woman who believes she is healthy because she is dieting and exercising each day and doesn't worry that she is not receiving her period. A woman who is not eating enough for the amount that she is exercising, is not giving her body enough nutrients and fuel to operate, the body's response is to shut off non-essential functions, such as the reproductive system. Women do not focus much attention on the affect this can have on their bone density. When a woman is operating at a low-estrogen state, she may fall into the early stages of osteoporosis, and experience a decrease in bone density. The bone loss she experiences at this time could be irreversible later in life, even if the woman chose to gain weight and body fat (4). Julia Stamps-Mallon, from Santa Rosa, California ran cross-country in high school, and despite the fact that she saw the nutritionist and had regular bone scans, she was not getting her period, and was not fully aware of the effects of osteoporosis early in life. "Within a year, the base of her spinal column broke mid-run and a fall from a skateboard shattered her leg" (3). Her bones had become so frail because of her low caloric intake and her high intensity workout.
While this has become a glaring issue in women's athletics, there is still much to be learned by females in sports today, and especially by coaches. When the National Collegiate Athletics Association (NCAA) surveyed over 2,800 coaches about disordered eating, only "19 percent of men and 26 percent of women were aware of the seriousness of amenorrhea, defined as a menstrual dysfunction for three or more months" (3). These extremely low numbers may have something to do with the national trend of women not paying much attention to their periods. A survey published by Health and Medicine Week found that nearly two-thirds of women do not use their periods as a monthly indicator of health, pregnancy, or fertility. They often choose, instead, to use birth control limiting the number of periods they have each year, rather than once a month, or on average, 13 per year, they are having as few as four each year (5). While this is a controlled method of receiving one's period, it reflects a general ideology that a period is not a valuable indicator of health and well-being. Steps are being taken, however, to educate more young female athletes and their coaches, the NCAA has even published a handbook available to coaches advising them to look for the signs of the female athlete triad, which include stress fractures, cold intolerance, and excessive use of the bathroom (3).
This is an issue that will be continued to be recognized and hopefully treated long into the future of women athletics. Women should, however, realize how fortunate they are that their body reacts in this way to the lack of nutrients in their system. Not allowing a woman to become pregnant if she is unable to survive the pregnancy and provide enough nutrients to the child acts as an evolutionary safeguard for the human population. While the ability to menstruate and reproduce seems to lie in the superficial measures of body fat and weight, real change takes place on a molecular level, and further research demonstrates the biological marvels of a woman's reproductive system. This information is relatively new in the scientific world, only truly receiving attention in the past ten years and there is still much more to learn, especially in the changing age of menarche, the onset of menstruation, in the United States. Girls are beginning to receive their periods at an increasingly younger age, and it is said to be directly affected by the changed level of hormones in foods from animals, such as milk from a cow that has been given extra hormones. It will be interesting to see the effect that this will have on the culture of many female sports where a preadolescent figure is so important, and women often don't begin their period until their late teens.
1) Angier, Natalie. "Chemical Tied to Fat Control Could Help Trigger Puberty." New York Times (1997): c1+. 16 Nov. 2006 <http://query.nytimes.com/gst/fullpage.html?se c=health&res=940 3E1D61339F934A35752C0A961958260>.
2) Frisch, Rose E. Female Fertility and the Body Fat Connection. The University of Chicago Press: Chicago, 2002.
3) Scott, Paul. "When Being Varsity- Fit Masks an Eating Disorder." New York Times (2006). 10 Nov. 2007 <http://www.nytimes.com/2006/09/14/fashion/14Fitness. html?ex=1315886400&en=88d395e97bab0adc&ei=5088&partner=rssnyt&emc=rss>. 4) Villarosa, Linda. "Tri-Fold Ailment Stalks Female Athletes." New York Times (1999): f7. 15 Nov. 2007 <http://query.nytimes.com/gst/fullpage.html?sec=health&res= 9407E FD7103BF931A15755C0A96F958260>.
5) "Women Don't Rely on Periods as Indicator of Pregnancy, Good Health, or Fertility." Health and Medicine Week (2002): 25. ProQuest. Bryn Mawr. 15 Nov. 2007 <http://proquest. umi.com/pqdweb?did=268100721&sid=2&Fmt=3&clientId= 42765&RQT=309&VName=PQD>.