Energy balance, not exercise, key to athletic menstrual disturbance

February 12, 2002

University Park, Pa. - Female athletes often lose their menstrual cycle when training strenuously, but researchers have long speculated on whether this infertility was due to low body fat, low weight or exercise itself. Now, researchers have shown that the cause of athletic amenorrhea is more likely a negative energy balance caused by increasing exercise without increasing food intake.

"A growing proportion of women are susceptible to losing their menstrual cycle when exercising strenuously," says Dr. Nancy I. Williams, assistant professor of kineseology and physiology at Penn State. "If women go six to 12 months without having a menstrual cycle, they could show bone loss. Bone densities in some long distance runners who have gone for a prolonged time period without having normal menstrual cycles can be very low."

In studies done with monkeys, which show menstrual cyclicity much like women, researchers showed that low energy availability associated with strenuous exercise training plays an important role in causing exercise-induced amenorrhea. These researchers, working at the University of Pittsburgh, published findings in the Journal of Clinical Endocrinology and Metabolism showing that exercise-induced amenorrhea was reversible in the monkeys by increasing food intake while the monkeys still exercised.

Williams worked with Judy L. Cameron, associate professor of psychiatry and cell biology and physiology at the University of Pittsburgh. Dana L. Helmreich and David B. Parfitt, then graduate students, and Anne Caston-Balderrama, at that time a post-doctoral fellow at the University of Pittsburgh, were also part of the research team. The researchers decided to look at an animal model to understand the causes of exercise-induced amenorrhea because it is difficult to closely control factors, such as eating habits and exercise, when studying humans. They chose cynomolgus monkeys because, like humans, they have a menstrual cycle of 28 days, ovulate in mid-cycle and show monthly periods of menses.

"It is difficult to obtain rigorous control in human studies, short of locking people up," says Williams.

Previous cross-sectional studies and short-term studies in humans had shown a correlation between changes in energy availability and changes in the menstrual cycle, but those studies were not definitive.

There was also some indication that metabolic states experienced by strenuously exercising women were similar to those in chronically calorie restricted people. However, whether the increased energy utilization which occurs with exercise or some other effect of exercise caused exercise-induced reproductive dysfunction was unknown.

"The idea that exercise or something about exercise is harmful to females was not definitively ruled out," says Williams. "That exercise itself is harmful would be a dangerous message to put out there. We needed to look at what it was about exercise that caused amenorrhea, what it was that suppresses ovulation. To do that, we needed a carefully controlled study."

After the researchers monitored normal menstrual cycles in eight monkeys for a few months, they trained the monkeys to run on treadmills, slowly increasing their daily training schedule to about six miles per day. Throughout the training period the amount of food provided remained the standard amount for a normal 4.5 to 7.5 pound monkey, although the researchers note that some monkeys did not finish all of their food all of the time.

The researchers found that during the study "there were no significant changes in body weight or caloric intake over the course of training and the development of amenorrhea." While body weight did not change, there were indications of an adaptation in energy expenditure. That is, the monkeys' metabolic hormones also changed, with a 20 percent drop in circulating thyroid hormone, suggesting that the suppression of ovulation is more closely related to negative energy balance than to a decrease in body weight.

To seal the conclusion that a negative energy balance was the key to exercise-induced amenorrhea, the researchers took four of the previous eight monkeys and, while keeping them on the same exercise program, provided them with more food than they were used to. All the monkeys eventually resumed normal menstrual cycles. However, those monkeys who increased their food consumption most rapidly and consumed the most additional food, resumed ovulation within as little as 12 to 16 days while those who increased their caloric intake more slowly, took almost two months to resume ovulation.

Williams is now conducting studies on women who agree to exercise and eat according to a prescribed regimen for four to six months. She is concerned because recreational exercisers have the first signs of ovulatory suppression and may easily be thrust into amenorrhea if energy availability declines. Many women that exercise also restrict their calories, consciously or unconsciously.

"Our goal is to test whether practical guidelines can be developed regarding the optimal balance between calories of food taken in and calories expended through exercise in order to maintain ovulation and regular menstrual cycles," says Williams. "This would then ensure that estrogen levels were also maintained at healthy levels. This is important because estrogen is a key hormone in the body for many physiological systems, influencing bone strength and cardiovascular health, not just reproduction."
-end-


Penn State

Related Body Weight Articles from Brightsurf:

Weight gainers more likely to underestimate their true body size
People with obesity who gain weight have a tendency to perceive their own body size as smaller than it actually is compared to those who maintain a stable weight, according to new research following more than 2,000 people with obesity from the Swedish Obese Subjects (SOS) study over 10 years.

Body weight has surprising, alarming impact on brain function
Amsterdam and Costa Mesa, CA, August 5, 2020 - As a person's weight goes up, all regions of the brain go down in activity and blood flow, according to a new brain imaging study in the Journal of Alzheimer's Disease.

Brain insulin sensitivity determines body weight and fat distribution
Just where fat is deposited in the body and to what degree a person may benefit from a lifestyle intervention depends on how sensitive the brain is to insulin.

Examining association between childhood video game use, adolescent body weight
Researchers looked at whether there was a long-term association between using video games at an early age and later weight as a teenager, as well as what role behaviors such as physical activity, the regularity of bedtimes and consuming sugar-sweetened beverages might play.

Brain receptor that regulates body heat may also help accelerate weight loss
The brain mechanism that enables us to maintain a constant body temperature may also be the key to rapid weight loss, a new study finds.

Short-term study suggests vegan diet can boost gut microbes related to body weight, body composition and blood sugar control
New research presented at this year's Annual Meeting of the European Association for the Study of Diabetes (EASD) in Barcelona, Spain (Sept.

Increased body weight in adolescent boys linked with heart attack before 65
A study in nearly 1.7 million 18-year-old boys has found that higher body mass index (BMI) is linked with greater risk of a heart attack before 65 years of age.

Excess weight and body fat cause cardiovascular disease
In the first Mendelian randomization study to look at this, researchers have found evidence that excess weight and body fat cause a range of heart and blood vessel diseases (rather than just being associated with it).

New brain mechanisms regulating body weight
Researchers at University of Gothenburg, Sweden, clarify the link between the molecule interleukine-6 (IL-6) in the brain and obesity.

Excess body weight before 50 is associated with higher risk of dying from pancreatic cancer
Excess weight before age 50 may be more strongly associated with pancreatic cancer mortality risk than excess weight at older ages, according to results of a study presented at the AACR Annual Meeting 2019, March 29-April 3.

Read More: Body Weight News and Body Weight Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.