Chronic Negative Energy Balance and Fertility: Is Your Exercise Program Affecting Your Ability to Conceive?

by Beth Heller, MS, RYT

Research published in the journal Obstetrics and Gynecology reports that women who exercised 4 hours or more times per week for 1-9 years were 40% less likely to have a live birth and were almost three times more likely to experience IVF cycle cancellation.  They were also twice as likely to have an implantation failure or pregnancy loss than women who did not report exercise.  This research reinforces previous data showing that strenuous exercise can disrupt reproductive hormone regulation.

A common question that arises at Pulling Down the Moon is whether or not women should give up exercise when trying to conceive (ttc) and/or undergoing A.R.T.  For many, exercise is an important tool for relieving depression, controlling stress and regulating body weight.  Putting the message out there that women who are "ttc" should abstain from exercise could be dangerous - we're already a highly sedentary society - but data such as the study referenced above suggest that we should look closer at the ways in which exercise can interact with our reproductive system.  An understanding of the mechanisms at work may help us make more intelligent exercise choices.

Another recent study dove into this question by comparing the menstrual cycles of sedentary and exercising women who were matched for age, body weight, BMI and age of menarch.  The results were astounding.  In the sedentary group, only 4% of women had menstrual dysfunction.  In the exercise group only 50% of cycles were ovulatory and 50% were abnormal.  Within the abnormal cycles,  29% demonstrated Luteal Phase Defect (a short luteal phase) and 20% were anovulatry.  In a further study of this same sample of women, the researchers found a correlation with “high-DT “(high drive for thinness) and menstrual dysfunction and found that REE (resting energy expenditure) was decreased in these women, a sign that they were experiencing negative metabolic effects of chronic negative energy balance.

So What Is Energy Balance?

Energy balance is a simple equation that nutritionists and exercise physiologists use to conceptualize the factors at work in weight loss and weight gain.  The energy balance equation is:

When Energy In = Energy Out, body weight is stable

When Energy In > Energy Out, there is weight gain

When Energy In < Energy Out, there is weight loss

Long-term negative energy balance in females is associated with decreases in circulating metabolic hormones (like thyroid hormone) that regulate overall metabolic rate, and with increases in baseline stress hormone levels like cortisol.  Often, shifts in energy balance can occur without weight loss, especially in long-term exercisers.  Call to mind that trim gal at the health club who spends 60 minutes a day on the elliptical trainer but never gets thinner.  While she may view the exercise session as justification for a candy bar, her body perceives it as a major “fight or flight event.”  Although her weight does not change, hormonal and metabolic shifts like the ones described above can still occur as the body slows down non-essential systems (like reproduction) to preserve energy.  Signs that a woman may be in negative energy balance are anovulatory cycles or the absence of menstrual periods.

Should Women Give Up Exercise when Trying to Conceive?

The answer to this question is a resounding "no!"  Exercise has also been shown to relieve depression, control stress and regulate a healthy body weight - all very important elements for conception.  What women do need to consider, however, is how to exercise in a way that is "fertility friendly."

Intensity:  When we talk about exercise intensity we are talking about how HARD your body works during a particular exercise activity.  Intensity of an exercise determines its energy requirement, or how many calories you burn while exercising.  Thus, excessive intense exercise can create  a negative energy balance.  This may be a good thing when a woman has significant weight to lose but it is not a good thing when she is at a healthy weight.

Impact:  Exercise can be either low- or high-impact.  High impact activity is and exercise in which both feet leave the ground.  Examples of high impact exercise are running, aerobic dance that involves jumping and jumping rope.  Spinning is also high impact, although this form of cycling exercise does not involve jumping, the intense resistance and sprinting used in spin classes can place enormous impact on joints and muscles.

In general, high impact exercise can be detrimental to fertility in one of two ways.  The first is through the production of endorphins.  Endorphins "natural pain killers" produced by the body in response to strenuous exercise.  While these chemicals serve to mask pain signals and allow us to enjoy long-duration, strenuous exercise, they can also disrupt reproductive hormone regulation.  Second, high impact exercise is generally more intense than low impact exercise, causing the excessive energy drain described above.

What’s the Right Exercise Mix for Fertility?

Fertility-Friendly Exercise: Fertility-friendly exercise is moderate-intensity (heart rate at 60-65% of maximum), low-impact and of medium duration (30-45 minutes, 3-4 times per week).

Good Exercise Modalities:  walking, swimming, recreational bike riding, resistance training and hatha yoga

Relaxation Training: Learning to relax through practices like breathing and meditation are an important part of any fitness program.  Taking 20 minutes a day to meditate or just breathe can help to reduce stress and lower circulating stress hormones.  In addition, cross-training and including rest days where the body can rebuild and restore is also very important.

Nourish Up through Diet: In two recent blogs, Nourishing Up for Fertility and Energy Balance for Fertility – A Holistic View we explore the idea of creating a nourishing lifestyle that changes the paradigm of daily life.

For many women, letting go of an intense exercise program can be difficult.  Services like acupuncture, massage and nutrition counseling available at Pulling Down the Moon can be very helpful in making the transition to a more nourishing and fertile lifestyle.  Click here to learn more/book an appointment.

Sources

1.  Morris SN Obstet Gynecol. 2006 Oct;108(4):938-45.

2.  De Souza MJ Hum Reprod. 2010 Feb;25(2):491-503. Epub 2009 Nov 26.

3.  Gibbs JC Int J Sport Nutr Exerc Metab. 2011 Aug;21(4):280-90.

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