Body Fat, Exercise and Fertility

By Wendy Chang, MD
Southern California Reproductive Center

Introduction

Numerous studies have repeatedly shown that women athletes who have a low body mass index, (“BMI”), have a difficult time starting a family. We have found with our patient population that a number of female athletes have a low BMI. This low BMI often translates into fertility problems. In fact studies have shown that approximately12% of infertility cases are due to being underweight or having a low BMI.

Body fat plays a significant role in reproduction. Sex hormones are fat soluble and they are stored in the body’s fat layers. Women that have a low BMI produce a reduced amount of estrogen which can lead to an abnormal menstrual cycle. Amenorrhea, or the lack of a menstrual cycle, is a result of a low BMI.

What is too thin and how does this affect fertility?

The ideal body weight from a medical perspective is not an exact science. Most of the literature suggests that if a woman’s BMI is less than 85% of her “normal” BMI than she is too thin. A reduced BMI may translate into difficulties conceiving.

One can determine their BMI by following this equation: multiply your weight (in pounds) by 705, divide the result by your height in inches, and divide that result by your height again. A normal BMI is between 19 and 25; you are considered underweight if you fall below 19, and overweight if you fall above 25.

The problem of having a low BMI does not affect every woman. A low BMI becomes a problem only when it starts to affect the menstrual cycle and specifically ovulation. It is possible to menstruate without ovulation. A woman should contact her physician if she encounters fertility problems without a change in her menstrual cycle.

As previously discussed the ideal level of BMI is not an exact science. Some women are naturally thin. If the correct diet pattern, exercise program and healthy lifestyle are followed there is usually nothing to worry about. If a woman is thin because of excessive exercise and poor dietary habits, her fertility and pregnancy success can be adversely affected.

What is considered excessive exercise?

Women come in all shapes and sizes and the amount of exercise that is appropriate for each woman varies. Some women may exercise in excess of three hours per day, seven days a week and will have no adverse affects from a fertility standpoint. Others may exercise only an hour a day, three days a week and have adverse consequences, again, from a fertility standpoint. When one is exercising the body produces endorphins. These hormones produce feelings of euphoria which is also known as the “runner’s high”. Endorphins also increase levels of prolactin, which the body releases for the production of breast milk. An increase in prolactin may decrease the possibility of pregnancy.

There are some classic symptoms that every female athlete should look for and try to correct with regards to their training regiment and fertility.

1) Physical Symptoms

Menstrual irregularities, unexplained loss of weight, elevated blood pressure, slower heart rate recovery, excessive muscle fatigue, decreased immunity, gastrointestinal disturbances, and loss of
appetite

2) Psychological Symptoms

Depression, decreased self-confidence, mood changes, lethargy, lack of concentration, anxiety, sleep disturbance, restlessness, and aggression.

In addition, female athletes who engage in excessive exercise and have poor dietary habits are at risk of developing a low BMI which may result in lower estrogen levels. It is very important for female athletes to maintain the correct amount of caloric intake while exercising in order to avoid lower estrogen levels.

Should a female athlete experience any of the above symptoms she should contact her physician.

Conclusion

Exercise and athletic competition is more than recreation for many women. Yet excessive training, poor diet and a low BMI can affect fertility. We believe that a smart training program for the female athlete consists of a realistic exercise program combined with sufficient sleep, a healthy diet and adequate caloric intake resulting in a healthy BMI. A healthy life structure provides the female athlete with the ability to not only compete effectively but also maintain her options with regards to fertility and her ability to have a family.